Ian & Stuart's Australian Mac: Not for Sale/Another.not.for.sale (Australia).iso/Dr. Doyle/perl.man

Text File | 1994-11-11 | 270KB | 7,195 lines

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     NNNNAAAAMMMMEEEE
          perl - Practical Extraction and Report Language

     SSSSYYYYNNNNOOOOPPPPSSSSIIIISSSS
          ppppeeeerrrrllll [options] filename args

     DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
          Perl is an interpreted language optimized for scanning
          arbitrary text files, extracting information from those text
          files, and printing reports based on that information.  It's
          also a good language for many system management tasks.  The
          language is intended to be practical (easy to use,
          efficient, complete) rather than beautiful (tiny, elegant,
          minimal).  It combines (in the author's opinion, anyway)
          some of the best features of C, sed, awk, and sh, so people
          familiar with those languages should have little difficulty
          with it.  (Language historians will also note some vestiges
          of csh, Pascal, and even BASIC-PLUS.)  Expression syntax
          corresponds quite closely to C expression syntax.  Unlike
          most Unix utilities, perl does not arbitrarily limit the
          size of your data--if you've got the memory, perl can slurp
          in your whole file as a single string.  Recursion is of
          unlimited depth.  And the hash tables used by associative
          arrays grow as necessary to prevent degraded performance.
          Perl uses sophisticated pattern matching techniques to scan
          large amounts of data very quickly.  Although optimized for
          scanning text, perl can also deal with binary data, and can
          make dbm files look like associative arrays (where dbm is
          available).  Setuid perl scripts are safer than C programs
          through a dataflow tracing mechanism which prevents many
          stupid security holes.  If you have a problem that would
          ordinarily use sed or awk or sh, but it exceeds their
          capabilities or must run a little faster, and you don't want
          to write the silly thing in C, then perl may be for you.
          There are also translators to turn your sed and awk scripts
          into perl scripts.  OK, enough hype.

          Upon startup, perl looks for your script in one of the
          following places:

          1.  Specified line by line via ----eeee switches on the command
              line.

          2.  Contained in the file specified by the first filename on
              the command line.  (Note that systems supporting the #!
              notation invoke interpreters this way.)

          3.  Passed in implicitly via standard input.  This only
              works if there are no filename arguments--to pass
              arguments to a stdin script you must explicitly specify
              a - for the script name.




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          After locating your script, perl compiles it to an internal
          form.  If the script is syntactically correct, it is
          executed.

          OOOOppppttttiiiioooonnnnssss

          Note: on first reading this section may not make much sense
          to you.  It's here at the front for easy reference.

          A single-character option may be combined with the following
          option, if any.  This is particularly useful when invoking a
          script using the #! construct which only allows one
          argument.  Example:

               #!/usr/bin/perl -spi.bak # same as -s -p -i.bak
               ...

          Options include:

          ----0000digits
               specifies the record separator ($/) as an octal number.
               If there are no digits, the null character is the
               separator.  Other switches may precede or follow the
               digits.  For example, if you have a version of find
               which can print filenames terminated by the null
               character, you can say this:

                   find . -name '*.bak' -print0 | perl -n0e unlink

               The special value 00 will cause Perl to slurp files in
               paragraph mode.  The value 0777 will cause Perl to
               slurp files whole since there is no legal character
               with that value.

          ----aaaa   turns on autosplit mode when used with a ----nnnn or ----pppp.  An
               implicit split command to the @F array is done as the
               first thing inside the implicit while loop produced by
               the ----nnnn or ----pppp.

                    perl -ane 'print pop(@F), "\n";'

               is equivalent to

                    while (<>) {
                         @F = split(' ');
                         print pop(@F), "\n";
                    }


          ----cccc   causes perl to check the syntax of the script and then
               exit without executing it.




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          ----dddd   runs the script under the perl debugger.  See the
               section on Debugging.

          ----DDDDnumber
               sets debugging flags.  To watch how it executes your
               script, use ----DDDD11114444.  (This only works if debugging is
               compiled into your perl.)  Another nice value is
               -D1024, which lists your compiled syntax tree.  And
               -D512 displays compiled regular expressions.

          ----eeee commandline
               may be used to enter one line of script.  Multiple ----eeee
               commands may be given to build up a multi-line script.
               If ----eeee is given, perl will not look for a script
               filename in the argument list.

          ----iiiiextension
               specifies that files processed by the <> construct are
               to be edited in-place.  It does this by renaming the
               input file, opening the output file by the same name,
               and selecting that output file as the default for print
               statements.  The extension, if supplied, is added to
               the name of the old file to make a backup copy.  If no
               extension is supplied, no backup is made.  Saying "perl
               -p -i.bak -e "s/foo/bar/;" ... " is the same as using
               the script:

                    #!/usr/bin/perl -pi.bak
                    s/foo/bar/;

               which is equivalent to

                    #!/usr/bin/perl
                    while (<>) {
                         if ($ARGV ne $oldargv) {
                              rename($ARGV, $ARGV . '.bak');
                              open(ARGVOUT, ">$ARGV");
                              select(ARGVOUT);
                              $oldargv = $ARGV;
                         }
                         s/foo/bar/;
                    }
                    continue {
                        print;     # this prints to original filename
                    }
                    select(STDOUT);

               except that the ----iiii form doesn't need to compare $ARGV
               to $oldargv to know when the filename has changed.  It
               does, however, use ARGVOUT for the selected filehandle.
               Note that STDOUT is restored as the default output
               filehandle after the loop.



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               You can use eof to locate the end of each input file,
               in case you want to append to each file, or reset line
               numbering (see example under eof).

          ----IIIIdirectory
               may be used in conjunction with ----PPPP to tell the C
               preprocessor where to look for include files.  By
               default /usr/include and /usr/lib/perl are searched.

          ----lllloctnum
               enables automatic line-ending processing.  It has two
               effects: first, it automatically chops the line
               terminator when used with ----nnnn or ----pppp ,,,, and second, it
               assigns $\ to have the value of octnum so that any
               print statements will have that line terminator added
               back on.  If octnum is omitted, sets $\ to the current
               value of $/.  For instance, to trim lines to 80
               columns:

                    perl -lpe 'substr($_, 80) = ""'

               Note that the assignment $\ = $/ is done when the
               switch is processed, so the input record separator can
               be different than the output record separator if the ----llll
               switch is followed by a ----0000 switch:

                    gnufind / -print0 | perl -ln0e 'print "found $_" if -p'

               This sets $\ to newline and then sets $/ to the null
               character.

          ----nnnn   causes perl to assume the following loop around your
               script, which makes it iterate over filename arguments
               somewhat like "sed -n" or awk:

                    while (<>) {
                         ...       # your script goes here
                    }

               Note that the lines are not printed by default.  See ----pppp
               to have lines printed.  Here is an efficient way to
               delete all files older than a week:

                    find . -mtime +7 -print | perl -nle 'unlink;'

               This is faster than using the -exec switch of find
               because you don't have to start a process on every
               filename found.

          ----pppp   causes perl to assume the following loop around your
               script, which makes it iterate over filename arguments
               somewhat like sed:



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                    while (<>) {
                         ...       # your script goes here
                    } continue {
                         print;
                    }

               Note that the lines are printed automatically.  To
               suppress printing use the ----nnnn switch.  A ----pppp overrides a
               ----nnnn switch.

          ----PPPP   causes your script to be run through the C preprocessor
               before compilation by perl.  (Since both comments and
               cpp directives begin with the # character, you should
               avoid starting comments with any words recognized by
               the C preprocessor such as "if", "else" or "define".)

          ----ssss   enables some rudimentary switch parsing for switches on
               the command line after the script name but before any
               filename arguments (or before a --).  Any switch found
               there is removed from @ARGV and sets the corresponding
               variable in the perl script.  The following script
               prints "true" if and only if the script is invoked with
               a -xyz switch.

                    #!/usr/bin/perl -s
                    if ($xyz) { print "true\n"; }


          ----SSSS   makes perl use the PATH environment variable to search
               for the script (unless the name of the script starts
               with a slash).  Typically this is used to emulate #!
               startup on machines that don't support #!, in the
               following manner:

                    #!/usr/bin/perl
                    eval "exec /usr/bin/perl -S $0 $*"
                         if $running_under_some_shell;

               The system ignores the first line and feeds the script
               to /bin/sh, which proceeds to try to execute the perl
               script as a shell script.  The shell executes the
               second line as a normal shell command, and thus starts
               up the perl interpreter.  On some systems $0 doesn't
               always contain the full pathname, so the ----SSSS tells perl
               to search for the script if necessary.  After perl
               locates the script, it parses the lines and ignores
               them because the variable $running_under_some_shell is
               never true.  A better construct than $* would be
               ${1+"$@"}, which handles embedded spaces and such in
               the filenames, but doesn't work if the script is being
               interpreted by csh.  In order to start up sh rather
               than csh, some systems may have to replace the #! line



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               with a line containing just a colon, which will be
               politely ignored by perl.  Other systems can't control
               that, and need a totally devious construct that will
               work under any of csh, sh or perl, such as the
               following:

                    eval '(exit $?0)' && eval 'exec /usr/bin/perl -S $0 ${1+"$@"}'
                    & eval 'exec /usr/bin/perl -S $0 $argv:q'
                         if 0;


          ----uuuu   causes perl to dump core after compiling your script.
               You can then take this core dump and turn it into an
               executable file by using the undump program (not
               supplied).  This speeds startup at the expense of some
               disk space (which you can minimize by stripping the
               executable).  (Still, a "hello world" executable comes
               out to about 200K on my machine.)  If you are going to
               run your executable as a set-id program then you should
               probably compile it using taintperl rather than normal
               perl.  If you want to execute a portion of your script
               before dumping, use the dump operator instead.  Note:
               availability of undump is platform specific and may not
               be available for a specific port of perl.

          ----UUUU   allows perl to do unsafe operations.  Currently the
               only "unsafe" operations are the unlinking of
               directories while running as superuser, and running
               setuid programs with fatal taint checks turned into
               warnings.

          ----vvvv   prints the version and patchlevel of your perl
               executable.

          ----wwww   prints warnings about identifiers that are mentioned
               only once, and scalar variables that are used before
               being set.  Also warns about redefined subroutines, and
               references to undefined filehandles or filehandles
               opened readonly that you are attempting to write on.
               Also warns you if you use == on values that don't look
               like numbers, and if your subroutines recurse more than
               100 deep.

          ----xxxxdirectory
               tells perl that the script is embedded in a message.
               Leading garbage will be discarded until the first line
               that starts with #! and contains the string "perl".
               Any meaningful switches on that line will be applied
               (but only one group of switches, as with normal #!
               processing).  If a directory name is specified, Perl
               will switch to that directory before running the
               script.  The ----xxxx switch only controls the the disposal



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               of leading garbage.  The script must be terminated with
               __END__ if there is trailing garbage to be ignored (the
               script can process any or all of the trailing garbage
               via the DATA filehandle if desired).

          DDDDaaaattttaaaa TTTTyyyyppppeeeessss aaaannnndddd OOOObbbbjjjjeeeeccccttttssss

          Perl has three data types: scalars, arrays of scalars, and
          associative arrays of scalars.  Normal arrays are indexed by
          number, and associative arrays by string.

          The interpretation of operations and values in perl
          sometimes depends on the requirements of the context around
          the operation or value.  There are three major contexts:
          string, numeric and array.  Certain operations return array
          values in contexts wanting an array, and scalar values
          otherwise.  (If this is true of an operation it will be
          mentioned in the documentation for that operation.)
          Operations which return scalars don't care whether the
          context is looking for a string or a number, but scalar
          variables and values are interpreted as strings or numbers
          as appropriate to the context.  A scalar is interpreted as
          TRUE in the boolean sense if it is not the null string or 0.
          Booleans returned by operators are 1 for true and 0 or ''
          (the null string) for false.

          There are actually two varieties of null string: defined and
          undefined.  Undefined null strings are returned when there
          is no real value for something, such as when there was an
          error, or at end of file, or when you refer to an
          uninitialized variable or element of an array.  An undefined
          null string may become defined the first time you access it,
          but prior to that you can use the defined() operator to
          determine whether the value is defined or not.

          References to scalar variables always begin with '$', even
          when referring to a scalar that is part of an array.  Thus:

              $days           # a simple scalar variable
              $days[28]       # 29th element of array @days
              $days{'Feb'}    # one value from an associative array
              $#days          # last index of array @days

          but entire arrays or array slices are denoted by '@':

              @days           # ($days[0], $days[1],... $days[n])
              @days[3,4,5]    # same as @days[3..5]
              @days{'a','c'}  # same as ($days{'a'},$days{'c'})

          and entire associative arrays are denoted by '%':

              %days           # (key1, val1, key2, val2 ...)



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          Any of these eight constructs may serve as an lvalue, that
          is, may be assigned to.  (It also turns out that an
          assignment is itself an lvalue in certain contexts--see
          examples under s, tr and chop.)  Assignment to a scalar
          evaluates the righthand side in a scalar context, while
          assignment to an array or array slice evaluates the
          righthand side in an array context.

          You may find the length of array @days by evaluating
          "$#days", as in csh.  (Actually, it's not the length of the
          array, it's the subscript of the last element, since there
          is (ordinarily) a 0th element.)  Assigning to $#days changes
          the length of the array.  Shortening an array by this method
          does not actually destroy any values.  Lengthening an array
          that was previously shortened recovers the values that were
          in those elements.  You can also gain some measure of
          efficiency by preextending an array that is going to get
          big.  (You can also extend an array by assigning to an
          element that is off the end of the array.  This differs from
          assigning to $#whatever in that intervening values are set
          to null rather than recovered.)  You can truncate an array
          down to nothing by assigning the null list () to it.  The
          following are exactly equivalent

               @whatever = ();
               $#whatever = $[ - 1;


          If you evaluate an array in a scalar context, it returns the
          length of the array.  The following is always true:

               scalar(@whatever) == $#whatever - $[ + 1;

          If you evaluate an associative array in a scalar context, it
          returns a value which is true if and only if the array
          contains any elements.  (If there are any elements, the
          value returned is a string consisting of the number of used
          buckets and the number of allocated buckets, separated by a
          slash.)

          Multi-dimensional arrays are not directly supported, but see
          the discussion of the $; variable later for a means of
          emulating multiple subscripts with an associative array.
          You could also write a subroutine to turn multiple
          subscripts into a single subscript.

          Every data type has its own namespace.  You can, without
          fear of conflict, use the same name for a scalar variable,
          an array, an associative array, a filehandle, a subroutine
          name, and/or a label.  Since variable and array references
          always start with '$', '@', or '%', the "reserved" words
          aren't in fact reserved with respect to variable names.



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          (They ARE reserved with respect to labels and filehandles,
          however, which don't have an initial special character.
          Hint: you could say open(LOG,'logfile') rather than
          open(log,'logfile').  Using uppercase filehandles also
          improves readability and protects you from conflict with
          future reserved words.)  Case IS significant--"FOO", "Foo"
          and "foo" are all different names.  Names which start with a
          letter may also contain digits and underscores.  Names which
          do not start with a letter are limited to one character,
          e.g. "$%" or "$$".  (Most of the one character names have a
          predefined significance to perl.  More later.)

          Numeric literals are specified in any of the usual floating
          point or integer formats:

              12345
              12345.67
              .23E-10
              0xffff     # hex
              0377  # octal
              4_294_967_296

          String literals are delimited by either single or double
          quotes.  They work much like shell quotes: double-quoted
          string literals are subject to backslash and variable
          substitution; single-quoted strings are not (except for \'
          and \\).  The usual backslash rules apply for making
          characters such as newline, tab, etc., as well as some more
          exotic forms:

               \t        tab
               \n        newline
               \r        return
               \f        form feed
               \b        backspace
               \a        alarm (bell)
               \e        escape
               \033      octal char
               \x1b      hex char
               \c[       control char
               \l        lowercase next char
               \u        uppercase next char
               \L        lowercase till \E
               \U        uppercase till \E
               \E        end case modification

          You can also embed newlines directly in your strings, i.e.
          they can end on a different line than they begin.  This is
          nice, but if you forget your trailing quote, the error will
          not be reported until perl finds another line containing the
          quote character, which may be much further on in the script.
          Variable substitution inside strings is limited to scalar



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          variables, normal array values, and array slices.  (In other
          words, identifiers beginning with $ or @, followed by an
          optional bracketed expression as a subscript.)  The
          following code segment prints out "The price is $100."

              $Price = '$100';               # not interpreted
              print "The price is $Price.\n";# interpreted

          Note that you can put curly brackets around the identifier
          to delimit it from following alphanumerics.  Also note that
          a single quoted string must be separated from a preceding
          word by a space, since single quote is a valid character in
          an identifier (see Packages).

          Two special literals are __LINE__ and __FILE__, which
          represent the current line number and filename at that point
          in your program.  They may only be used as separate tokens;
          they will not be interpolated into strings.  In addition,
          the token __END__ may be used to indicate the logical end of
          the script before the actual end of file.  Any following
          text is ignored, but may be read via the DATA filehandle.
          (The DATA filehandle may read data only from the main
          script, but not from any required file or evaluated string.)
          The two control characters ^D and ^Z are synonyms for
          __END__.

          A word that doesn't have any other interpretation in the
          grammar will be treated as if it had single quotes around
          it.  For this purpose, a word consists only of alphanumeric
          characters and underline, and must start with an alphabetic
          character.  As with filehandles and labels, a bare word that
          consists entirely of lowercase letters risks conflict with
          future reserved words, and if you use the ----wwww switch, Perl
          will warn you about any such words.

          Array values are interpolated into double-quoted strings by
          joining all the elements of the array with the delimiter
          specified in the $" variable, space by default.  (Since in
          versions of perl prior to 3.0 the @ character was not a
          metacharacter in double-quoted strings, the interpolation of
          @array, $array[EXPR], @array[LIST], $array{EXPR}, or
          @array{LIST} only happens if array is referenced elsewhere
          in the program or is predefined.)  The following are
          equivalent:

               $temp = join($",@ARGV);
               system "echo $temp";

               system "echo @ARGV";

          Within search patterns (which also undergo double-quotish
          substitution) there is a bad ambiguity:  Is /$foo[bar]/ to



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          be interpreted as /${foo}[bar]/ (where [bar] is a character
          class for the regular expression) or as /${foo[bar]}/ (where
          [bar] is the subscript to array @foo)?  If @foo doesn't
          otherwise exist, then it's obviously a character class.  If
          @foo exists, perl takes a good guess about [bar], and is
          almost always right.  If it does guess wrong, or if you're
          just plain paranoid, you can force the correct
          interpretation with curly brackets as above.

          A line-oriented form of quoting is based on the shell here-
          is syntax.  Following a << you specify a string to terminate
          the quoted material, and all lines following the current
          line down to the terminating string are the value of the
          item.  The terminating string may be either an identifier (a
          word), or some quoted text.  If quoted, the type of quotes
          you use determines the treatment of the text, just as in
          regular quoting.  An unquoted identifier works like double
          quotes.  There must be no space between the << and the
          identifier.  (If you put a space it will be treated as a
          null identifier, which is valid, and matches the first blank
          line--see Merry Christmas example below.)  The terminating
          string must appear by itself (unquoted and with no
          surrounding whitespace) on the terminating line.

               print <<EOF;        # same as above
          The price is $Price.
          EOF

               print <<"EOF";      # same as above
          The price is $Price.
          EOF

               print << x 10;      # null identifier is delimiter
          Merry Christmas!

               print <<`EOC`;      # execute commands
          echo hi there
          echo lo there
          EOC

               print <<foo, <<bar; # you can stack them
          I said foo.
          foo
          I said bar.
          bar

          Array literals are denoted by separating individual values
          by commas, and enclosing the list in parentheses:

               (LIST)

          In a context not requiring an array value, the value of the



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          array literal is the value of the final element, as in the C
          comma operator.  For example,

              @foo = ('cc', '-E', $bar);

          assigns the entire array value to array foo, but

              $foo = ('cc', '-E', $bar);

          assigns the value of variable bar to variable foo.  Note
          that the value of an actual array in a scalar context is the
          length of the array; the following assigns to $foo the value
          3:

              @foo = ('cc', '-E', $bar);
              $foo = @foo;         # $foo gets 3

          You may have an optional comma before the closing
          parenthesis of an array literal, so that you can say:

              @foo = (
               1,
               2,
               3,
              );

          When a LIST is evaluated, each element of the list is
          evaluated in an array context, and the resulting array value
          is interpolated into LIST just as if each individual element
          were a member of LIST.  Thus arrays lose their identity in a
          LIST--the list

               (@foo,@bar,&SomeSub)

          contains all the elements of @foo followed by all the
          elements of @bar, followed by all the elements returned by
          the subroutine named SomeSub.

          A list value may also be subscripted like a normal array.
          Examples:

               $time = (stat($file))[8];     # stat returns array value
               $digit = ('a','b','c','d','e','f')[$digit-10];
               return (pop(@foo),pop(@foo))[0];


          Array lists may be assigned to if and only if each element
          of the list is an lvalue:

              ($a, $b, $c) = (1, 2, 3);

              ($map{'red'}, $map{'blue'}, $map{'green'}) = (0x00f, 0x0f0, 0xf00);



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          The final element may be an array or an associative array:

              ($a, $b, @rest) = split;
              local($a, $b, %rest) = @_;

          You can actually put an array anywhere in the list, but the
          first array in the list will soak up all the values, and
          anything after it will get a null value.  This may be useful
          in a local().

          An associative array literal contains pairs of values to be
          interpreted as a key and a value:

              # same as map assignment above
              %map = ('red',0x00f,'blue',0x0f0,'green',0xf00);

          Array assignment in a scalar context returns the number of
          elements produced by the expression on the right side of the
          assignment:

               $x = (($foo,$bar) = (3,2,1)); # set $x to 3, not 2


          There are several other pseudo-literals that you should know
          about.  If a string is enclosed by backticks (grave
          accents), it first undergoes variable substitution just like
          a double quoted string.  It is then interpreted as a
          command, and the output of that command is the value of the
          pseudo-literal, like in a shell.  In a scalar context, a
          single string consisting of all the output is returned.  In
          an array context, an array of values is returned, one for
          each line of output.  (You can set $/ to use a different
          line terminator.)  The command is executed each time the
          pseudo-literal is evaluated.  The status value of the
          command is returned in $? (see Predefined Names for the
          interpretation of $?).  Unlike in csh, no translation is
          done on the return data--newlines remain newlines.  Unlike
          in any of the shells, single quotes do not hide variable
          names in the command from interpretation.  To pass a $
          through to the shell you need to hide it with a backslash.

          Evaluating a filehandle in angle brackets yields the next
          line from that file (newline included, so it's never false
          until EOF, at which time an undefined value is returned).
          Ordinarily you must assign that value to a variable, but
          there is one situation where an automatic assignment
          happens.  If (and only if) the input symbol is the only
          thing inside the conditional of a while loop, the value is
          automatically assigned to the variable "$_".  (This may seem
          like an odd thing to you, but you'll use the construct in
          almost every perl script you write.)  Anyway, the following
          lines are equivalent to each other:



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              while ($_ = <STDIN>) { print; }
              while (<STDIN>) { print; }
              for (;<STDIN>;) { print; }
              print while $_ = <STDIN>;
              print while <STDIN>;

          The filehandles STDIN, STDOUT and STDERR are predefined.
          (The filehandles stdin, stdout and stderr will also work
          except in packages, where they would be interpreted as local
          identifiers rather than global.)  Additional filehandles may
          be created with the open function.

          If a <FILEHANDLE> is used in a context that is looking for
          an array, an array consisting of all the input lines is
          returned, one line per array element.  It's easy to make a
          LARGE data space this way, so use with care.

          The null filehandle <> is special and can be used to emulate
          the behavior of sed and awk.  Input from <> comes either
          from standard input, or from each file listed on the command
          line.  Here's how it works: the first time <> is evaluated,
          the ARGV array is checked, and if it is null, $ARGV[0] is
          set to '-', which when opened gives you standard input.  The
          ARGV array is then processed as a list of filenames.  The
          loop

               while (<>) {
                    ...            # code for each line
               }

          is equivalent to the following Perl-like pseudo code:

               unshift(@ARGV, '-') if $#ARGV < $[;
               while ($ARGV = shift) {
                    open(ARGV, $ARGV);
                    while (<ARGV>) {
                         ...       # code for each line
                    }
               }

          except that it isn't as cumbersome to say, and will actually
          work.  It really does shift array ARGV and put the current
          filename into variable ARGV.  It also uses filehandle ARGV
          internally--<> is just a synonym for <ARGV>, which is
          magical.  (The pseudo code above doesn't work because it
          treats <ARGV> as non-magical.)

          You can modify @ARGV before the first <> as long as the
          array ends up containing the list of filenames you really
          want.  Line numbers ($.) continue as if the input was one
          big happy file.  (But see example under eof for how to reset
          line numbers on each file.)



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          If you want to set @ARGV to your own list of files, go right
          ahead.  If you want to pass switches into your script, you
          can put a loop on the front like this:

               while ($_ = $ARGV[0], /^-/) {
                    shift;
                   last if /^--$/;
                    /^-D(.*)/ && ($debug = $1);
                    /^-v/ && $verbose++;
                    ...       # other switches
               }
               while (<>) {
                    ...       # code for each line
               }

          The <> symbol will return FALSE only once.  If you call it
          again after this it will assume you are processing another
          @ARGV list, and if you haven't set @ARGV, will input from
          STDIN.

          If the string inside the angle brackets is a reference to a
          scalar variable (e.g. <$foo>), then that variable contains
          the name of the filehandle to input from.

          If the string inside angle brackets is not a filehandle, it
          is interpreted as a filename pattern to be globbed, and
          either an array of filenames or the next filename in the
          list is returned, depending on context.  One level of $
          interpretation is done first, but you can't say <$foo>
          because that's an indirect filehandle as explained in the
          previous paragraph.  You could insert curly brackets to
          force interpretation as a filename glob: <${foo}>.  Example:

               while (<*.c>) {
                    chmod 0644, $_;
               }

          is equivalent to

               open(foo, "echo *.c | tr -s ' \t\r\f' '\\012\\012\\012\\012'|");
               while (<foo>) {
                    chop;
                    chmod 0644, $_;
               }

          In fact, it's currently implemented that way.  (Which means
          it will not work on filenames with spaces in them unless you
          have /bin/csh on your machine.)  Of course, the shortest way
          to do the above is:

               chmod 0644, <*.c>;




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          SSSSyyyynnnnttttaaaaxxxx

          A perl script consists of a sequence of declarations and
          commands.  The only things that need to be declared in perl
          are report formats and subroutines.  See the sections below
          for more information on those declarations.  All
          uninitialized user-created objects are assumed to start with
          a null or 0 value until they are defined by some explicit
          operation such as assignment.  The sequence of commands is
          executed just once, unlike in sed and awk scripts, where the
          sequence of commands is executed for each input line.  While
          this means that you must explicitly loop over the lines of
          your input file (or files), it also means you have much more
          control over which files and which lines you look at.
          (Actually, I'm lying--it is possible to do an implicit loop
          with either the ----nnnn or ----pppp switch.)

          A declaration can be put anywhere a command can, but has no
          effect on the execution of the primary sequence of
          commands--declarations all take effect at compile time.
          Typically all the declarations are put at the beginning or
          the end of the script.

          Perl is, for the most part, a free-form language.  (The only
          exception to this is format declarations, for fairly obvious
          reasons.)  Comments are indicated by the # character, and
          extend to the end of the line.  If you attempt to use /* */
          C comments, it will be interpreted either as division or
          pattern matching, depending on the context.  So don't do
          that.

          CCCCoooommmmppppoooouuuunnnndddd ssssttttaaaatttteeeemmmmeeeennnnttttssss

          In perl, a sequence of commands may be treated as one
          command by enclosing it in curly brackets.  We will call
          this a BLOCK.

          The following compound commands may be used to control flow:

               if (EXPR) BLOCK
               if (EXPR) BLOCK else BLOCK
               if (EXPR) BLOCK elsif (EXPR) BLOCK ... else BLOCK
               LABEL while (EXPR) BLOCK
               LABEL while (EXPR) BLOCK continue BLOCK
               LABEL for (EXPR; EXPR; EXPR) BLOCK
               LABEL foreach VAR (ARRAY) BLOCK
               LABEL BLOCK continue BLOCK

          Note that, unlike C and Pascal, these are defined in terms
          of BLOCKs, not statements.  This means that the curly
          brackets are required--no dangling statements allowed.  If
          you want to write conditionals without curly brackets there



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          are several other ways to do it.  The following all do the
          same thing:

               if (!open(foo)) { die "Can't open $foo: $!"; }
               die "Can't open $foo: $!" unless open(foo);
               open(foo) || die "Can't open $foo: $!"; # foo or bust!
               open(foo) ? 'hi mom' : die "Can't open $foo: $!";
                              # a bit exotic, that last one


          The if statement is straightforward.  Since BLOCKs are
          always bounded by curly brackets, there is never any
          ambiguity about which if an else goes with.  If you use
          unless in place of if, the sense of the test is reversed.

          The while statement executes the block as long as the
          expression is true (does not evaluate to the null string or
          0).  The LABEL is optional, and if present, consists of an
          identifier followed by a colon.  The LABEL identifies the
          loop for the loop control statements next, last, and redo
          (see below).  If there is a continue BLOCK, it is always
          executed just before the conditional is about to be
          evaluated again, similarly to the third part of a for loop
          in C.  Thus it can be used to increment a loop variable,
          even when the loop has been continued via the next statement
          (similar to the C "continue" statement).

          If the word while is replaced by the word until, the sense
          of the test is reversed, but the conditional is still tested
          before the first iteration.

          In either the if or the while statement, you may replace
          "(EXPR)" with a BLOCK, and the conditional is true if the
          value of the last command in that block is true.

          The for loop works exactly like the corresponding while
          loop:

               for ($i = 1; $i < 10; $i++) {
                    ...
               }

          is the same as

               $i = 1;
               while ($i < 10) {
                    ...
               } continue {
                    $i++;
               }

          The foreach loop iterates over a normal array value and sets



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          the variable VAR to be each element of the array in turn.
          The variable is implicitly local to the loop, and regains
          its former value upon exiting the loop.  The "foreach"
          keyword is actually identical to the "for" keyword, so you
          can use "foreach" for readability or "for" for brevity.  If
          VAR is omitted, $_ is set to each value.  If ARRAY is an
          actual array (as opposed to an expression returning an array
          value), you can modify each element of the array by
          modifying VAR inside the loop.  Examples:

               for (@ary) { s/foo/bar/; }

               foreach $elem (@elements) {
                    $elem *= 2;
               }

               for ((10,9,8,7,6,5,4,3,2,1,'BOOM')) {
                    print $_, "\n"; sleep(1);
               }

               for (1..15) { print "Merry Christmas\n"; }

               foreach $item (split(/:[\\\n:]*/, $ENV{'TERMCAP'})) {
                    print "Item: $item\n";
               }


          The BLOCK by itself (labeled or not) is equivalent to a loop
          that executes once.  Thus you can use any of the loop
          control statements in it to leave or restart the block.  The
          continue block is optional.  This construct is particularly
          nice for doing case structures.

               foo: {
                    if (/^abc/) { $abc = 1; last foo; }
                    if (/^def/) { $def = 1; last foo; }
                    if (/^xyz/) { $xyz = 1; last foo; }
                    $nothing = 1;
               }

          There is no official switch statement in perl, because there
          are already several ways to write the equivalent.  In
          addition to the above, you could write

               foo: {
                    $abc = 1, last foo  if /^abc/;
                    $def = 1, last foo  if /^def/;
                    $xyz = 1, last foo  if /^xyz/;
                    $nothing = 1;
               }

          or



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               foo: {
                    /^abc/ && do { $abc = 1; last foo; };
                    /^def/ && do { $def = 1; last foo; };
                    /^xyz/ && do { $xyz = 1; last foo; };
                    $nothing = 1;
               }

          or

               foo: {
                    /^abc/ && ($abc = 1, last foo);
                    /^def/ && ($def = 1, last foo);
                    /^xyz/ && ($xyz = 1, last foo);
                    $nothing = 1;
               }

          or even

               if (/^abc/)
                    { $abc = 1; }
               elsif (/^def/)
                    { $def = 1; }
               elsif (/^xyz/)
                    { $xyz = 1; }
               else
                    {$nothing = 1;}

          As it happens, these are all optimized internally to a
          switch structure, so perl jumps directly to the desired
          statement, and you needn't worry about perl executing a lot
          of unnecessary statements when you have a string of 50
          elsifs, as long as you are testing the same simple scalar
          variable using ==, eq, or pattern matching as above.  (If
          you're curious as to whether the optimizer has done this for
          a particular case statement, you can use the -D1024 switch
          to list the syntax tree before execution.)

          SSSSiiiimmmmpppplllleeee ssssttttaaaatttteeeemmmmeeeennnnttttssss

          The only kind of simple statement is an expression evaluated
          for its side effects.  Every simple statement must be
          terminated with a semicolon, unless it is the final
          statement in a block, in which case the semicolon is
          optional.  (Semicolon is still encouraged there if the block
          takes up more than one line).

          Any simple statement may optionally be followed by a single
          modifier, just before the terminating semicolon.  The
          possible modifiers are:






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               if EXPR
               unless EXPR
               while EXPR
               until EXPR

          The if and unless modifiers have the expected semantics.
          The while and until modifiers also have the expected
          semantics (conditional evaluated first), except when applied
          to a do-BLOCK or a do-SUBROUTINE command, in which case the
          block executes once before the conditional is evaluated.
          This is so that you can write loops like:

               do {
                    $_ = <STDIN>;
                    ...
               } until $_ eq ".\n";

          (See the do operator below.  Note also that the loop control
          commands described later will NOT work in this construct,
          since modifiers don't take loop labels.  Sorry.)

          EEEExxxxpppprrrreeeessssssssiiiioooonnnnssss

          Since perl expressions work almost exactly like C
          expressions, only the differences will be mentioned here.

          Here's what perl has that C doesn't:

          **      The exponentiation operator.

          **=     The exponentiation assignment operator.

          ()      The null list, used to initialize an array to null.

          .       Concatenation of two strings.

          .=      The concatenation assignment operator.

          eq      String equality (== is numeric equality).  For a
                  mnemonic just think of "eq" as a string.  (If you
                  are used to the awk behavior of using == for either
                  string or numeric equality based on the current form
                  of the comparands, beware!  You must be explicit
                  here.)

          ne      String inequality (!= is numeric inequality).

          lt      String less than.

          gt      String greater than.





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          le      String less than or equal.

          ge      String greater than or equal.

          cmp     String comparison, returning -1, 0, or 1.

          <=>     Numeric comparison, returning -1, 0, or 1.

          =~      Certain operations search or modify the string "$_"
                  by default.  This operator makes that kind of
                  operation work on some other string.  The right
                  argument is a search pattern, substitution, or
                  translation.  The left argument is what is supposed
                  to be searched, substituted, or translated instead
                  of the default "$_".  The return value indicates the
                  success of the operation.  (If the right argument is
                  an expression other than a search pattern,
                  substitution, or translation, it is interpreted as a
                  search pattern at run time.  This is less efficient
                  than an explicit search, since the pattern must be
                  compiled every time the expression is evaluated.)
                  The precedence of this operator is lower than unary
                  minus and autoincrement/decrement, but higher than
                  everything else.

          !~      Just like =~ except the return value is negated.

          x       The repetition operator.  Returns a string
                  consisting of the left operand repeated the number
                  of times specified by the right operand.  In an
                  array context, if the left operand is a list in
                  parens, it repeats the list.

                       print '-' x 80;          # print row of dashes
                       print '-' x80;      # illegal, x80 is identifier

                       print "\t" x ($tab/8), ' ' x ($tab%8);  # tab over

                       @ones = (1) x 80;        # an array of 80 1's
                       @ones = (5) x @ones;          # set all elements to 5


          x=      The repetition assignment operator.  Only works on
                  scalars.

          ..      The range operator, which is really two different
                  operators depending on the context.  In an array
                  context, returns an array of values counting (by
                  ones) from the left value to the right value.  This
                  is useful for writing "for (1..10)" loops and for
                  doing slice operations on arrays.




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                  In a scalar context, .. returns a boolean value.
                  The operator is bistable, like a flip-flop, and
                  emulates the line-range (comma) operator of sed,
                  awk, and various editors.  Each .. operator
                  maintains its own boolean state.  It is false as
                  long as its left operand is false.  Once the left
                  operand is true, the range operator stays true until
                  the right operand is true, AFTER which the range
                  operator becomes false again.  (It doesn't become
                  false till the next time the range operator is
                  evaluated.  It can test the right operand and become
                  false on the same evaluation it became true (as in
                  awk), but it still returns true once.  If you don't
                  want it to test the right operand till the next
                  evaluation (as in sed), use three dots (...) instead
                  of two.)  The right operand is not evaluated while
                  the operator is in the "false" state, and the left
                  operand is not evaluated while the operator is in
                  the "true" state.  The precedence is a little lower
                  than || and &&.  The value returned is either the
                  null string for false, or a sequence number
                  (beginning with 1) for true.  The sequence number is
                  reset for each range encountered.  The final
                  sequence number in a range has the string 'E0'
                  appended to it, which doesn't affect its numeric
                  value, but gives you something to search for if you
                  want to exclude the endpoint.  You can exclude the
                  beginning point by waiting for the sequence number
                  to be greater than 1.  If either operand of scalar
                  .. is static, that operand is implicitly compared to
                  the $. variable, the current line number.  Examples:

                  As a scalar operator:
                      if (101 .. 200) { print; }     # print 2nd hundred lines

                      next line if (1 .. /^$/); # skip header lines

                      s/^/> / if (/^$/ .. eof());    # quote body

                  As an array operator:
                      for (101 .. 200) { print; }    # print $_ 100 times

                      @foo = @foo[$[ .. $#foo]; # an expensive no-op
                      @foo = @foo[$#foo-4 .. $#foo]; # slice last 5 items


          -x      A file test.  This unary operator takes one
                  argument, either a filename or a filehandle, and
                  tests the associated file to see if something is
                  true about it.  If the argument is omitted, tests
                  $_, except for -t, which tests STDIN.  It returns 1
                  for true and '' for false, or the undefined value if



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                  the file doesn't exist.  Precedence is higher than
                  logical and relational operators, but lower than
                  arithmetic operators.  The operator may be any of:
                       -r   File is readable by effective uid/gid.
                       -w   File is writable by effective uid/gid.
                       -x   File is executable by effective uid/gid.
                       -o   File is owned by effective uid.
                       -R   File is readable by real uid/gid.
                       -W   File is writable by real uid/gid.
                       -X   File is executable by real uid/gid.
                       -O   File is owned by real uid.
                       -e   File exists.
                       -z   File has zero size.
                       -s   File has non-zero size (returns size).
                       -f   File is a plain file.
                       -d   File is a directory.
                       -l   File is a symbolic link.
                       -p   File is a named pipe (FIFO).
                       -S   File is a socket.
                       -b   File is a block special file.
                       -c   File is a character special file.
                       -u   File has setuid bit set.
                       -g   File has setgid bit set.
                       -k   File has sticky bit set.
                       -t   Filehandle is opened to a tty.
                       -T   File is a text file.
                       -B   File is a binary file (opposite of -T).
                       -M   Age of file in days when script started.
                       -A   Same for access time.
                       -C   Same for inode change time.

                  The interpretation of the file permission operators
                  -r, -R, -w, -W, -x and -X is based solely on the
                  mode of the file and the uids and gids of the user.
                  There may be other reasons you can't actually read,
                  write or execute the file.  Also note that, for the
                  superuser, -r, -R, -w and -W always return 1, and -x
                  and -X return 1 if any execute bit is set in the
                  mode.  Scripts run by the superuser may thus need to
                  do a stat() in order to determine the actual mode of
                  the file, or temporarily set the uid to something
                  else.

                  Example:

                       while (<>) {
                            chop;
                            next unless -f $_;  # ignore specials
                            ...
                       }

                  Note that -s/a/b/ does not do a negated



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                  substitution.  Saying -exp($foo) still works as
                  expected, however--only single letters following a
                  minus are interpreted as file tests.

                  The -T and -B switches work as follows.  The first
                  block or so of the file is examined for odd
                  characters such as strange control codes or
                  metacharacters.  If too many odd characters (>10%)
                  are found, it's a -B file, otherwise it's a -T file.
                  Also, any file containing null in the first block is
                  considered a binary file.  If -T or -B is used on a
                  filehandle, the current stdio buffer is examined
                  rather than the first block.  Both -T and -B return
                  TRUE on a null file, or a file at EOF when testing a
                  filehandle.

          If any of the file tests (or either stat operator) are given
          the special filehandle consisting of a solitary underline,
          then the stat structure of the previous file test (or stat
          operator) is used, saving a system call.  (This doesn't work
          with -t, and you need to remember that lstat and -l will
          leave values in the stat structure for the symbolic link,
          not the real file.)  Example:

               print "Can do.\n" if -r $a || -w _ || -x _;

               stat($filename);
               print "Readable\n" if -r _;
               print "Writable\n" if -w _;
               print "Executable\n" if -x _;
               print "Setuid\n" if -u _;
               print "Setgid\n" if -g _;
               print "Sticky\n" if -k _;
               print "Text\n" if -T _;
               print "Binary\n" if -B _;


          Here is what C has that perl doesn't:

          unary &     Address-of operator.

          unary *     Dereference-address operator.

          (TYPE)      Type casting operator.

          Like C, perl does a certain amount of expression evaluation
          at compile time, whenever it determines that all of the
          arguments to an operator are static and have no side
          effects.  In particular, string concatenation happens at
          compile time between literals that don't do variable
          substitution.  Backslash interpretation also happens at
          compile time.  You can say



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               'Now is the time for all' . "\n" .
               'good men to come to.'

          and this all reduces to one string internally.

          The autoincrement operator has a little extra built-in magic
          to it.  If you increment a variable that is numeric, or that
          has ever been used in a numeric context, you get a normal
          increment.  If, however, the variable has only been used in
          string contexts since it was set, and has a value that is
          not null and matches the pattern /^[a-zA-Z]*[0-9]*$/, the
          increment is done as a string, preserving each character
          within its range, with carry:

               print ++($foo = '99');   # prints '100'
               print ++($foo = 'a0');   # prints 'a1'
               print ++($foo = 'Az');   # prints 'Ba'
               print ++($foo = 'zz');   # prints 'aaa'

          The autodecrement is not magical.

          The range operator (in an array context) makes use of the
          magical autoincrement algorithm if the minimum and maximum
          are strings.  You can say

               @alphabet = ('A' .. 'Z');

          to get all the letters of the alphabet, or

               $hexdigit = (0 .. 9, 'a' .. 'f')[$num & 15];

          to get a hexadecimal digit, or

               @z2 = ('01' .. '31');  print @z2[$mday];

          to get dates with leading zeros.  (If the final value
          specified is not in the sequence that the magical increment
          would produce, the sequence goes until the next value would
          be longer than the final value specified.)

          The || and && operators differ from C's in that, rather than
          returning 0 or 1, they return the last value evaluated.
          Thus, a portable way to find out the home directory might
          be:

               $home = $ENV{'HOME'} || $ENV{'LOGDIR'} ||
                   (getpwuid($<))[7] || die "You're homeless!\n";


          Along with the literals and variables mentioned earlier, the
          operations in the following section can serve as terms in an
          expression.  Some of these operations take a LIST as an



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          argument.  Such a list can consist of any combination of
          scalar arguments or array values; the array values will be
          included in the list as if each individual element were
          interpolated at that point in the list, forming a longer
          single-dimensional array value.  Elements of the LIST should
          be separated by commas.  If an operation is listed both with
          and without parentheses around its arguments, it means you
          can either use it as a unary operator or as a function call.
          To use it as a function call, the next token on the same
          line must be a left parenthesis.  (There may be intervening
          white space.)  Such a function then has highest precedence,
          as you would expect from a function.  If any token other
          than a left parenthesis follows, then it is a unary
          operator, with a precedence depending only on whether it is
          a LIST operator or not.  LIST operators have lowest
          precedence.  All other unary operators have a precedence
          greater than relational operators but less than arithmetic
          operators.  See the section on Precedence.

          For operators that can be used in either a scalar or array
          context, failure is generally indicated in a scalar context
          by returning the undefined value, and in an array context by
          returning the null list.  Remember though that THERE IS NO
          GENERAL RULE FOR CONVERTING A LIST INTO A SCALAR.  Each
          operator decides which sort of scalar it would be most
          appropriate to return.  Some operators return the length of
          the list that would have been returned in an array context.
          Some operators return the first value in the list.  Some
          operators return the last value in the list.  Some operators
          return a count of successful operations.  In general, they
          do what you want, unless you want consistency.

          /PATTERN/
                  See m/PATTERN/.

          ?PATTERN?
                  This is just like the /pattern/ search, except that
                  it matches only once between calls to the reset
                  operator.  This is a useful optimization when you
                  only want to see the first occurrence of something
                  in each file of a set of files, for instance.  Only
                  ?? patterns local to the current package are reset.

          accept(NEWSOCKET,GENERICSOCKET)
                  Does the same thing that the accept system call
                  does.  Returns true if it succeeded, false
                  otherwise.  See example in section on Interprocess
                  Communication.

          alarm(SECONDS)





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          alarm SECONDS
                  Arranges to have a SIGALRM delivered to this process
                  after the specified number of seconds (minus 1,
                  actually) have elapsed.  Thus, alarm(15) will cause
                  a SIGALRM at some point more than 14 seconds in the
                  future.  Only one timer may be counting at once.
                  Each call disables the previous timer, and an
                  argument of 0 may be supplied to cancel the previous
                  timer without starting a new one.  The returned
                  value is the amount of time remaining on the
                  previous timer.

          atan2(Y,X)
                  Returns the arctangent of Y/X in the range -PI to
                  PI.

          bind(SOCKET,NAME)
                  Does the same thing that the bind system call does.
                  Returns true if it succeeded, false otherwise.  NAME
                  should be a packed address of the proper type for
                  the socket.  See example in section on Interprocess
                  Communication.

          binmode(FILEHANDLE)

          binmode FILEHANDLE
                  Arranges for the file to be read in "binary" mode in
                  operating systems that distinguish between binary
                  and text files.  Files that are not read in binary
                  mode have CR LF sequences translated to LF on input
                  and LF translated to CR LF on output.  Binmode has
                  no effect under Unix.  If FILEHANDLE is an
                  expression, the value is taken as the name of the
                  filehandle.

          caller(EXPR)

          caller  Returns the context of the current subroutine call:

                       ($package,$filename,$line) = caller;

                  With EXPR, returns some extra information that the
                  debugger uses to print a stack trace.  The value of
                  EXPR indicates how many call frames to go back
                  before the current one.

          chdir(EXPR)

          chdir EXPR
                  Changes the working directory to EXPR, if possible.
                  If EXPR is omitted, changes to home directory.
                  Returns 1 upon success, 0 otherwise.  See example



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                  under die.

          chmod(LIST)

          chmod LIST
                  Changes the permissions of a list of files.  The
                  first element of the list must be the numerical
                  mode.  Returns the number of files successfully
                  changed.

                       $cnt = chmod 0755, 'foo', 'bar';
                       chmod 0755, @executables;


          chop(LIST)

          chop(VARIABLE)

          chop VARIABLE

          chop    Chops off the last character of a string and returns
                  the character chopped.  It's used primarily to
                  remove the newline from the end of an input record,
                  but is much more efficient than s/\n// because it
                  neither scans nor copies the string.  If VARIABLE is
                  omitted, chops $_.  Example:

                       while (<>) {
                            chop;     # avoid \n on last field
                            @array = split(/:/);
                            ...
                       }

                  You can actually chop anything that's an lvalue,
                  including an assignment:

                       chop($cwd = `pwd`);
                       chop($answer = <STDIN>);

                  If you chop a list, each element is chopped.  Only
                  the value of the last chop is returned.

          chown(LIST)

          chown LIST
                  Changes the owner (and group) of a list of files.
                  The first two elements of the list must be the
                  NUMERICAL uid and gid, in that order.  Returns the
                  number of files successfully changed.

                       $cnt = chown $uid, $gid, 'foo', 'bar';
                       chown $uid, $gid, @filenames;



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                  Here's an example that looks up non-numeric uids in
                  the passwd file:

                       print "User: ";
                       $user = <STDIN>;
                       chop($user);
                       print "Files: "
                       $pattern = <STDIN>;
                       chop($pattern);
                       open(pass, '/etc/passwd')
                            || die "Can't open passwd: $!\n";
                       while (<pass>) {
                            ($login,$pass,$uid,$gid) = split(/:/);
                            $uid{$login} = $uid;
                            $gid{$login} = $gid;
                       }
                       @ary = <${pattern}>;     # get filenames
                       if ($uid{$user} eq '') {
                            die "$user not in passwd file";
                       }
                       else {
                            chown $uid{$user}, $gid{$user}, @ary;
                       }


          chroot(FILENAME)

          chroot FILENAME
                  Does the same as the system call of that name.  If
                  you don't know what it does, don't worry about it.
                  If FILENAME is omitted, does chroot to $_.

          close(FILEHANDLE)

          close FILEHANDLE
                  Closes the file or pipe associated with the file
                  handle.  You don't have to close FILEHANDLE if you
                  are immediately going to do another open on it,
                  since open will close it for you.  (See open.)
                  However, an explicit close on an input file resets
                  the line counter ($.), while the implicit close done
                  by open does not.  Also, closing a pipe will wait
                  for the process executing on the pipe to complete,
                  in case you want to look at the output of the pipe
                  afterwards.  Closing a pipe explicitly also puts the
                  status value of the command into $?.  Example:

                       open(OUTPUT, '|sort >foo');   # pipe to sort
                       ...  # print stuff to output
                       close OUTPUT;       # wait for sort to finish
                       open(INPUT, 'foo'); # get sort's results




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                  FILEHANDLE may be an expression whose value gives
                  the real filehandle name.

          closedir(DIRHANDLE)

          closedir DIRHANDLE
                  Closes a directory opened by opendir().

          connect(SOCKET,NAME)
                  Does the same thing that the connect system call
                  does.  Returns true if it succeeded, false
                  otherwise.  NAME should be a package address of the
                  proper type for the socket.  See example in section
                  on Interprocess Communication.

          cos(EXPR)

          cos EXPR
                  Returns the cosine of EXPR (expressed in radians).
                  If EXPR is omitted takes cosine of $_.

          crypt(PLAINTEXT,SALT)
                  Encrypts a string exactly like the crypt() function
                  in the C library.  Useful for checking the password
                  file for lousy passwords.  Only the guys wearing
                  white hats should do this.

          dbmclose(ASSOC_ARRAY)

          dbmclose ASSOC_ARRAY
                  Breaks the binding between a dbm file and an
                  associative array.  The values remaining in the
                  associative array are meaningless unless you happen
                  to want to know what was in the cache for the dbm
                  file.  This function is only useful if you have
                  ndbm.

          dbmopen(ASSOC,DBNAME,MODE)
                  This binds a dbm or ndbm file to an associative
                  array.  ASSOC is the name of the associative array.
                  (Unlike normal open, the first argument is NOT a
                  filehandle, even though it looks like one).  DBNAME
                  is the name of the database (without the .dir or
                  .pag extension).  If the database does not exist, it
                  is created with protection specified by MODE (as
                  modified by the umask).  If your system only
                  supports the older dbm functions, you may perform
                  only one dbmopen in your program.  If your system
                  has neither dbm nor ndbm, calling dbmopen produces a
                  fatal error.

                  Values assigned to the associative array prior to



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                  the dbmopen are lost.  A certain number of values
                  from the dbm file are cached in memory.  By default
                  this number is 64, but you can increase it by
                  preallocating that number of garbage entries in the
                  associative array before the dbmopen.  You can flush
                  the cache if necessary with the reset command.

                  If you don't have write access to the dbm file, you
                  can only read associative array variables, not set
                  them.  If you want to test whether you can write,
                  either use file tests or try setting a dummy array
                  entry inside an eval, which will trap the error.

                  Note that functions such as keys() and values() may
                  return huge array values when used on large dbm
                  files.  You may prefer to use the each() function to
                  iterate over large dbm files.  Example:

                       # print out history file offsets
                       dbmopen(HIST,'/usr/lib/news/history',0666);
                       while (($key,$val) = each %HIST) {
                            print $key, ' = ', unpack('L',$val), "\n";
                       }
                       dbmclose(HIST);


          defined(EXPR)

          defined EXPR
                  Returns a boolean value saying whether the lvalue
                  EXPR has a real value or not.  Many operations
                  return the undefined value under exceptional
                  conditions, such as end of file, uninitialized
                  variable, system error and such.  This function
                  allows you to distinguish between an undefined null
                  string and a defined null string with operations
                  that might return a real null string, in particular
                  referencing elements of an array.  You may also
                  check to see if arrays or subroutines exist.  Use on
                  predefined variables is not guaranteed to produce
                  intuitive results.  Examples:

                       print if defined $switch{'D'};
                       print "$val\n" while defined($val = pop(@ary));
                       die "Can't readlink $sym: $!"
                            unless defined($value = readlink $sym);
                       eval '@foo = ()' if defined(@foo);
                       die "No XYZ package defined" unless defined %_XYZ;
                       sub foo { defined &$bar ? &$bar(@_) : die "No bar"; }

                  See also undef.




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          delete $ASSOC{KEY}
                  Deletes the specified value from the specified
                  associative array.  Returns the deleted value, or
                  the undefined value if nothing was deleted.
                  Deleting from $ENV{} modifies the environment.
                  Deleting from an array bound to a dbm file deletes
                  the entry from the dbm file.

                  The following deletes all the values of an
                  associative array:

                       foreach $key (keys %ARRAY) {
                            delete $ARRAY{$key};
                       }

                  (But it would be faster to use the reset command.
                  Saying undef %ARRAY is faster yet.)

          die(LIST)

          die LIST
                  Outside of an eval, prints the value of LIST to
                  STDERR and exits with the current value of $!
                  (errno).  If $! is 0, exits with the value of ($? >>
                  8) (`command` status).  If ($? >> 8) is 0, exits
                  with 255.  Inside an eval, the error message is
                  stuffed into $@ and the eval is terminated with the
                  undefined value.

                  Equivalent examples:

                       die "Can't cd to spool: $!\n"
                            unless chdir '/usr/spool/news';

                       chdir '/usr/spool/news' || die "Can't cd to spool: $!\n"


                  If the value of EXPR does not end in a newline, the
                  current script line number and input line number (if
                  any) are also printed, and a newline is supplied.
                  Hint: sometimes appending ", stopped" to your
                  message will cause it to make better sense when the
                  string "at foo line 123" is appended.  Suppose you
                  are running script "canasta".

                       die "/etc/games is no good";
                       die "/etc/games is no good, stopped";

                  produce, respectively

                       /etc/games is no good at canasta line 123.
                       /etc/games is no good, stopped at canasta line 123.



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                  See also exit.

          do BLOCK
                  Returns the value of the last command in the
                  sequence of commands indicated by BLOCK.  When
                  modified by a loop modifier, executes the BLOCK once
                  before testing the loop condition.  (On other
                  statements the loop modifiers test the conditional
                  first.)

          do SUBROUTINE (LIST)
                  Executes a SUBROUTINE declared by a sub declaration,
                  and returns the value of the last expression
                  evaluated in SUBROUTINE.  If there is no subroutine
                  by that name, produces a fatal error.  (You may use
                  the "defined" operator to determine if a subroutine
                  exists.)  If you pass arrays as part of LIST you may
                  wish to pass the length of the array in front of
                  each array.  (See the section on subroutines later
                  on.)  The parentheses are required to avoid
                  confusion with the "do EXPR" form.

                  SUBROUTINE may also be a single scalar variable, in
                  which case the name of the subroutine to execute is
                  taken from the variable.

                  As an alternate (and preferred) form, you may call a
                  subroutine by prefixing the name with an ampersand:
                  &foo(@args).  If you aren't passing any arguments,
                  you don't have to use parentheses.  If you omit the
                  parentheses, no @_ array is passed to the
                  subroutine.  The & form is also used to specify
                  subroutines to the defined and undef operators:

                       if (defined &$var) { &$var($parm); undef &$var; }


          do EXPR Uses the value of EXPR as a filename and executes
                  the contents of the file as a perl script.  Its
                  primary use is to include subroutines from a perl
                  subroutine library.

                       do 'stat.pl';

                  is just like

                       eval `cat stat.pl`;

                  except that it's more efficient, more concise, keeps
                  track of the current filename for error messages,
                  and searches all the ----IIII libraries if the file isn't
                  in the current directory (see also the @INC array in



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                  Predefined Names).  It's the same, however, in that
                  it does reparse the file every time you call it, so
                  if you are going to use the file inside a loop you
                  might prefer to use -P and #include, at the expense
                  of a little more startup time.  (The main problem
                  with #include is that cpp doesn't grok # comments--a
                  workaround is to use ";#" for standalone comments.)
                  Note that the following are NOT equivalent:

                       do $foo;  # eval a file
                       do $foo();     # call a subroutine

                  Note that inclusion of library routines is better
                  done with the "require" operator.

          dump LABEL
                  This causes an immediate core dump.  Primarily this
                  is so that you can use the undump program to turn
                  your core dump into an executable binary after
                  having initialized all your variables at the
                  beginning of the program.  When the new binary is
                  executed it will begin by executing a "goto LABEL"
                  (with all the restrictions that goto suffers).
                  Think of it as a goto with an intervening core dump
                  and reincarnation.  If LABEL is omitted, restarts
                  the program from the top.  WARNING: any files opened
                  at the time of the dump will NOT be open any more
                  when the program is reincarnated, with possible
                  resulting confusion on the part of perl.  See also
                  -u.

                  Example:

                       #!/usr/bin/perl
                       require 'getopt.pl';
                       require 'stat.pl';
                       %days = (
                           'Sun',1,
                           'Mon',2,
                           'Tue',3,
                           'Wed',4,
                           'Thu',5,
                           'Fri',6,
                           'Sat',7);

                       dump QUICKSTART if $ARGV[0] eq '-d';

                      QUICKSTART:
                       do Getopt('f');






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          each(ASSOC_ARRAY)

          each ASSOC_ARRAY
                  Returns a 2 element array consisting of the key and
                  value for the next value of an associative array, so
                  that you can iterate over it.  Entries are returned
                  in an apparently random order.  When the array is
                  entirely read, a null array is returned (which when
                  assigned produces a FALSE (0) value).  The next call
                  to each() after that will start iterating again.
                  The iterator can be reset only by reading all the
                  elements from the array.  You must not modify the
                  array while iterating over it.  There is a single
                  iterator for each associative array, shared by all
                  each(), keys() and values() function calls in the
                  program.  The following prints out your environment
                  like the printenv program, only in a different
                  order:

                       while (($key,$value) = each %ENV) {
                            print "$key=$value\n";
                       }

                  See also keys() and values().

          eof(FILEHANDLE)

          eof()

          eof     Returns 1 if the next read on FILEHANDLE will return
                  end of file, or if FILEHANDLE is not open.
                  FILEHANDLE may be an expression whose value gives
                  the real filehandle name.  (Note that this function
                  actually reads a character and then ungetc's it, so
                  it is not very useful in an interactive context.)
                  An eof without an argument returns the eof status
                  for the last file read.  Empty parentheses () may be
                  used to indicate the pseudo file formed of the files
                  listed on the command line, i.e. eof() is reasonable
                  to use inside a while (<>) loop to detect the end of
                  only the last file.  Use eof(ARGV) or eof without
                  the parentheses to test EACH file in a while (<>)
                  loop.  Examples:

                       # insert dashes just before last line of last file
                       while (<>) {
                            if (eof()) {
                                 print "--------------\n";
                            }
                            print;
                       }




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                       # reset line numbering on each input file
                       while (<>) {
                            print "$.\t$_";
                            if (eof) {     # Not eof().
                                 close(ARGV);
                            }
                       }


          eval(EXPR)

          eval EXPR

          eval BLOCK
                  EXPR is parsed and executed as if it were a little
                  perl program.  It is executed in the context of the
                  current perl program, so that any variable settings,
                  subroutine or format definitions remain afterwards.
                  The value returned is the value of the last
                  expression evaluated, just as with subroutines.  If
                  there is a syntax error or runtime error, or a die
                  statement is executed, an undefined value is
                  returned by eval, and $@ is set to the error
                  message.  If there was no error, $@ is guaranteed to
                  be a null string.  If EXPR is omitted, evaluates $_.
                  The final semicolon, if any, may be omitted from the
                  expression.

                  Note that, since eval traps otherwise-fatal errors,
                  it is useful for determining whether a particular
                  feature (such as dbmopen or symlink) is implemented.
                  It is also Perl's exception trapping mechanism,
                  where the die operator is used to raise exceptions.

                  If the code to be executed doesn't vary, you may use
                  the eval-BLOCK form to trap run-time errors without
                  incurring the penalty of recompiling each time.  The
                  error, if any, is still returned in $@.  Evaluating
                  a single-quoted string (as EXPR) has the same
                  effect, except that the eval-EXPR form reports
                  syntax errors at run time via $@, whereas the eval-
                  BLOCK form reports syntax errors at compile time.
                  The eval-EXPR form is optimized to eval-BLOCK the
                  first time it succeeds.  (Since the replacement side
                  of a substitution is considered a single-quoted
                  string when you use the e modifier, the same
                  optimization occurs there.)  Examples:








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                       # make divide-by-zero non-fatal
                       eval { $answer = $a / $b; }; warn $@ if $@;

                       # optimized to same thing after first use
                       eval '$answer = $a / $b'; warn $@ if $@;

                       # a compile-time error
                       eval { $answer = };

                       # a run-time error
                       eval '$answer =';   # sets $@


          exec(LIST)

          exec LIST
                  If there is more than one argument in LIST, or if
                  LIST is an array with more than one value, calls
                  execvp() with the arguments in LIST.  If there is
                  only one scalar argument, the argument is checked
                  for shell metacharacters.  If there are any, the
                  entire argument is passed to "/bin/sh -c" for
                  parsing.  If there are none, the argument is split
                  into words and passed directly to execvp(), which is
                  more efficient.  Note: exec (and system) do not
                  flush your output buffer, so you may need to set $|
                  to avoid lost output.  Examples:

                       exec '/bin/echo', 'Your arguments are: ', @ARGV;
                       exec "sort $outfile | uniq";


                  If you don't really want to execute the first
                  argument, but want to lie to the program you are
                  executing about its own name, you can specify the
                  program you actually want to run by assigning that
                  to a variable and putting the name of the variable
                  in front of the LIST without a comma.  (This always
                  forces interpretation of the LIST as a multi-valued
                  list, even if there is only a single scalar in the
                  list.)  Example:

                       $shell = '/bin/csh';
                       exec $shell '-sh';       # pretend it's a login shell


          exit(EXPR)

          exit EXPR
                  Evaluates EXPR and exits immediately with that
                  value.  Example:




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                       $ans = <STDIN>;
                       exit 0 if $ans =~ /^[Xx]/;

                  See also die.  If EXPR is omitted, exits with 0
                  status.

          exp(EXPR)

          exp EXPR
                  Returns e to the power of EXPR.  If EXPR is omitted,
                  gives exp($_).

          fcntl(FILEHANDLE,FUNCTION,SCALAR)
                  Implements the fcntl(2) function.  You'll probably
                  have to say

                       require "fcntl.ph"; # probably /usr/local/lib/perl/fcntl.ph

                  first to get the correct function definitions.  If
                  fcntl.ph doesn't exist or doesn't have the correct
                  definitions you'll have to roll your own, based on
                  your C header files such as <sys/fcntl.h>.  (There
                  is a perl script called h2ph that comes with the
                  perl kit which may help you in this.)  Argument
                  processing and value return works just like ioctl
                  below.  Note that fcntl will produce a fatal error
                  if used on a machine that doesn't implement
                  fcntl(2).

          fileno(FILEHANDLE)

          fileno FILEHANDLE
                  Returns the file descriptor for a filehandle.
                  Useful for constructing bitmaps for select().  If
                  FILEHANDLE is an expression, the value is taken as
                  the name of the filehandle.

          flock(FILEHANDLE,OPERATION)
                  Calls flock(2) on FILEHANDLE.  See manual page for
                  flock(2) for definition of OPERATION.  Returns true
                  for success, false on failure.  Will produce a fatal
                  error if used on a machine that doesn't implement
                  flock(2).  Here's a mailbox appender for BSD
                  systems.











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                       $LOCK_SH = 1;
                       $LOCK_EX = 2;
                       $LOCK_NB = 4;
                       $LOCK_UN = 8;

                       sub lock {
                           flock(MBOX,$LOCK_EX);
                           # and, in case someone appended
                           # while we were waiting...
                           seek(MBOX, 0, 2);
                       }

                       sub unlock {
                           flock(MBOX,$LOCK_UN);
                       }

                       open(MBOX, ">>/usr/spool/mail/$ENV{'USER'}")
                            || die "Can't open mailbox: $!";

                       do lock();
                       print MBOX $msg,"\n\n";
                       do unlock();


          fork    Does a fork() call.  Returns the child pid to the
                  parent process and 0 to the child process.  Note:
                  unflushed buffers remain unflushed in both
                  processes, which means you may need to set $| to
                  avoid duplicate output.

          getc(FILEHANDLE)

          getc FILEHANDLE

          getc    Returns the next character from the input file
                  attached to FILEHANDLE, or a null string at EOF.  If
                  FILEHANDLE is omitted, reads from STDIN.

          getlogin
                  Returns the current login from /etc/utmp, if any.
                  If null, use getpwuid.

                       $login = getlogin || (getpwuid($<))[0] ||
                  "Somebody";


          getpeername(SOCKET)
                  Returns the packed sockaddr address of other end of
                  the SOCKET connection.






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                       # An internet sockaddr
                       $sockaddr = 'S n a4 x8';
                       $hersockaddr = getpeername(S);
                       ($family, $port, $heraddr) =
                                 unpack($sockaddr,$hersockaddr);


          getpgrp(PID)

          getpgrp PID
                  Returns the current process group for the specified
                  PID, 0 for the current process.  Will produce a
                  fatal error if used on a machine that doesn't
                  implement getpgrp(2).  If EXPR is omitted, returns
                  process group of current process.

          getppid Returns the process id of the parent process.

          getpriority(WHICH,WHO)
                  Returns the current priority for a process, a
                  process group, or a user.  (See getpriority(2).)
                  Will produce a fatal error if used on a machine that
                  doesn't implement getpriority(2).

          getpwnam(NAME)

          getgrnam(NAME)

          gethostbyname(NAME)

          getnetbyname(NAME)

          getprotobyname(NAME)

          getpwuid(UID)

          getgrgid(GID)

          getservbyname(NAME,PROTO)

          gethostbyaddr(ADDR,ADDRTYPE)

          getnetbyaddr(ADDR,ADDRTYPE)

          getprotobynumber(NUMBER)

          getservbyport(PORT,PROTO)

          getpwent

          getgrent




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          gethostent

          getnetent

          getprotoent

          getservent

          setpwent

          setgrent

          sethostent(STAYOPEN)

          setnetent(STAYOPEN)

          setprotoent(STAYOPEN)

          setservent(STAYOPEN)

          endpwent

          endgrent

          endhostent

          endnetent

          endprotoent

          endservent
                  These routines perform the same functions as their
                  counterparts in the system library.  Within an array
                  context, the return values from the various get
                  routines are as follows:

                       ($name,$passwd,$uid,$gid,
                          $quota,$comment,$gcos,$dir,$shell) = getpw...
                       ($name,$passwd,$gid,$members) = getgr...
                       ($name,$aliases,$addrtype,$length,@addrs) = gethost...
                       ($name,$aliases,$addrtype,$net) = getnet...
                       ($name,$aliases,$proto) = getproto...
                       ($name,$aliases,$port,$proto) = getserv...

                  (If the entry doesn't exist you get a null list.)

                  Within a scalar context, you get the name, unless
                  the function was a lookup by name, in which case you
                  get the other thing, whatever it is.  (If the entry
                  doesn't exist you get the undefined value.)  For
                  example:




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                       $uid = getpwnam
                       $name = getpwuid
                       $name = getpwent
                       $gid = getgrnam
                       $name = getgrgid
                       $name = getgrent
                       etc.

                  The $members value returned by getgr... is a space
                  separated list of the login names of the members of
                  the group.

                  For the gethost... functions, if the h_errno
                  variable is supported in C, it will be returned to
                  you via $? if the function call fails.  The @addrs
                  value returned by a successful call is a list of the
                  raw addresses returned by the corresponding system
                  library call.  In the Internet domain, each address
                  is four bytes long and you can unpack it by saying
                  something like:

                       ($a,$b,$c,$d) = unpack('C4',$addr[0]);


          getsockname(SOCKET)
                  Returns the packed sockaddr address of this end of
                  the SOCKET connection.

                       # An internet sockaddr
                       $sockaddr = 'S n a4 x8';
                       $mysockaddr = getsockname(S);
                       ($family, $port, $myaddr) =
                                 unpack($sockaddr,$mysockaddr);


          getsockopt(SOCKET,LEVEL,OPTNAME)
                  Returns the socket option requested, or undefined if
                  there is an error.

          gmtime(EXPR)

          gmtime EXPR
                  Converts a time as returned by the time function to
                  a 9-element array with the time analyzed for the
                  Greenwich timezone.  Typically used as follows:

                  ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
                                                gmtime(time);

                  All array elements are numeric, and come straight
                  out of a struct tm.  In particular this means that
                  $mon has the range 0..11 and $wday has the range



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                  0..6.  If EXPR is omitted, does gmtime(time).

          goto LABEL
                  Finds the statement labeled with LABEL and resumes
                  execution there.  Currently you may only go to
                  statements in the main body of the program that are
                  not nested inside a do {} construct.  This statement
                  is not implemented very efficiently, and is here
                  only to make the sed-to-perl translator easier.  I
                  may change its semantics at any time, consistent
                  with support for translated sed scripts.  Use it at
                  your own risk.  Better yet, don't use it at all.

          grep(EXPR,LIST)
                  Evaluates EXPR for each element of LIST (locally
                  setting $_ to each element) and returns the array
                  value consisting of those elements for which the
                  expression evaluated to true.  In a scalar context,
                  returns the number of times the expression was true.

                       @foo = grep(!/^#/, @bar);    # weed out comments

                  Note that, since $_ is a reference into the array
                  value, it can be used to modify the elements of the
                  array.  While this is useful and supported, it can
                  cause bizarre results if the LIST is not a named
                  array.

          hex(EXPR)

          hex EXPR
                  Returns the decimal value of EXPR interpreted as an
                  hex string.  (To interpret strings that might start
                  with 0 or 0x see oct().)  If EXPR is omitted, uses
                  $_.

          index(STR,SUBSTR,POSITION)

          index(STR,SUBSTR)
                  Returns the position of the first occurrence of
                  SUBSTR in STR at or after POSITION.  If POSITION is
                  omitted, starts searching from the beginning of the
                  string.  The return value is based at 0, or whatever
                  you've set the $[ variable to.  If the substring is
                  not found, returns one less than the base,
                  ordinarily -1.

          int(EXPR)

          int EXPR
                  Returns the integer portion of EXPR.  If EXPR is
                  omitted, uses $_.



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          ioctl(FILEHANDLE,FUNCTION,SCALAR)
                  Implements the ioctl(2) function.  You'll probably
                  have to say

                       require "ioctl.ph"; # probably /usr/local/lib/perl/ioctl.ph

                  first to get the correct function definitions.  If
                  ioctl.ph doesn't exist or doesn't have the correct
                  definitions you'll have to roll your own, based on
                  your C header files such as <sys/ioctl.h>.  (There
                  is a perl script called h2ph that comes with the
                  perl kit which may help you in this.)  SCALAR will
                  be read and/or written depending on the FUNCTION--a
                  pointer to the string value of SCALAR will be passed
                  as the third argument of the actual ioctl call.  (If
                  SCALAR has no string value but does have a numeric
                  value, that value will be passed rather than a
                  pointer to the string value.  To guarantee this to
                  be true, add a 0 to the scalar before using it.)
                  The pack() and unpack() functions are useful for
                  manipulating the values of structures used by
                  ioctl().  The following example sets the erase
                  character to DEL.

                       require 'ioctl.ph';
                       $sgttyb_t = "ccccs";          # 4 chars and a short
                       if (ioctl(STDIN,$TIOCGETP,$sgttyb)) {
                            @ary = unpack($sgttyb_t,$sgttyb);
                            $ary[2] = 127;
                            $sgttyb = pack($sgttyb_t,@ary);
                            ioctl(STDIN,$TIOCSETP,$sgttyb)
                                 || die "Can't ioctl: $!";
                       }

                  The return value of ioctl (and fcntl) is as follows:

                       if OS returns:           perl returns:
                         -1                       undefined value
                         0                        string "0 but true"
                         anything else            that number

                  Thus perl returns true on success and false on
                  failure, yet you can still easily determine the
                  actual value returned by the operating system:

                       ($retval = ioctl(...)) || ($retval = -1);
                       printf "System returned %d\n", $retval;








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          join(EXPR,LIST)

          join(EXPR,ARRAY)
                  Joins the separate strings of LIST or ARRAY into a
                  single string with fields separated by the value of
                  EXPR, and returns the string.  Example:

                  $_ = join(':',
                            $login,$passwd,$uid,$gid,$gcos,$home,$shell);

                  See split.

          keys(ASSOC_ARRAY)

          keys ASSOC_ARRAY
                  Returns a normal array consisting of all the keys of
                  the named associative array.  The keys are returned
                  in an apparently random order, but it is the same
                  order as either the values() or each() function
                  produces (given that the associative array has not
                  been modified).  Here is yet another way to print
                  your environment:

                       @keys = keys %ENV;
                       @values = values %ENV;
                       while ($#keys >= 0) {
                            print pop(@keys), '=', pop(@values), "\n";
                       }

                  or how about sorted by key:

                       foreach $key (sort(keys %ENV)) {
                            print $key, '=', $ENV{$key}, "\n";
                       }


          kill(LIST)

          kill LIST
                  Sends a signal to a list of processes.  The first
                  element of the list must be the signal to send.
                  Returns the number of processes successfully
                  signaled.

                       $cnt = kill 1, $child1, $child2;
                       kill 9, @goners;

                  If the signal is negative, kills process groups
                  instead of processes.  (On System V, a negative
                  process number will also kill process groups, but
                  that's not portable.)  You may use a signal name in
                  quotes.



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          last LABEL

          last    The last command is like the break statement in C
                  (as used in loops); it immediately exits the loop in
                  question.  If the LABEL is omitted, the command
                  refers to the innermost enclosing loop.  The
                  continue block, if any, is not executed:

                       line: while (<STDIN>) {
                            last line if /^$/;  # exit when done with header
                            ...
                       }


          length(EXPR)

          length EXPR
                  Returns the length in characters of the value of
                  EXPR.  If EXPR is omitted, returns length of $_.

          link(OLDFILE,NEWFILE)
                  Creates a new filename linked to the old filename.
                  Returns 1 for success, 0 otherwise.

          listen(SOCKET,QUEUESIZE)
                  Does the same thing that the listen system call
                  does.  Returns true if it succeeded, false
                  otherwise.  See example in section on Interprocess
                  Communication.

          local(LIST)
                  Declares the listed variables to be local to the
                  enclosing block, subroutine, eval or "do".  All the
                  listed elements must be legal lvalues.  This
                  operator works by saving the current values of those
                  variables in LIST on a hidden stack and restoring
                  them upon exiting the block, subroutine or eval.
                  This means that called subroutines can also
                  reference the local variable, but not the global
                  one.  The LIST may be assigned to if desired, which
                  allows you to initialize your local variables.  (If
                  no initializer is given for a particular variable,
                  it is created with an undefined value.)  Commonly
                  this is used to name the parameters to a subroutine.
                  Examples:










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                       sub RANGEVAL {
                            local($min, $max, $thunk) = @_;
                            local($result) = '';
                            local($i);

                            # Presumably $thunk makes reference to $i

                            for ($i = $min; $i < $max; $i++) {
                                 $result .= eval $thunk;
                            }

                            $result;
                       }

                       if ($sw eq '-v') {
                           # init local array with global array
                           local(@ARGV) = @ARGV;
                           unshift(@ARGV,'echo');
                           system @ARGV;
                       }
                       # @ARGV restored

                       # temporarily add to digits associative array
                       if ($base12) {
                            # (NOTE: not claiming this is efficient!)
                            local(%digits) = (%digits,'t',10,'e',11);
                            do parse_num();
                       }

                  Note that local() is a run-time command, and so gets
                  executed every time through a loop, using up more
                  stack storage each time until it's all released at
                  once when the loop is exited.

          localtime(EXPR)

          localtime EXPR
                  Converts a time as returned by the time function to
                  a 9-element array with the time analyzed for the
                  local timezone.  Typically used as follows:

                  ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
                                                localtime(time);

                  All array elements are numeric, and come straight
                  out of a struct tm.  In particular this means that
                  $mon has the range 0..11 and $wday has the range
                  0..6.  If EXPR is omitted, does localtime(time).

          log(EXPR)





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          log EXPR
                  Returns logarithm (base e) of EXPR.  If EXPR is
                  omitted, returns log of $_.

          lstat(FILEHANDLE)

          lstat FILEHANDLE

          lstat(EXPR)

          lstat SCALARVARIABLE
                  Does the same thing as the stat() function, but
                  stats a symbolic link instead of the file the
                  symbolic link points to.  If symbolic links are
                  unimplemented on your system, a normal stat is done.

          m/PATTERN/gio

          /PATTERN/gio
                  Searches a string for a pattern match, and returns
                  true (1) or false ('').  If no string is specified
                  via the =~ or !~ operator, the $_ string is
                  searched.  (The string specified with =~ need not be
                  an lvalue--it may be the result of an expression
                  evaluation, but remember the =~ binds rather
                  tightly.)  See also the section on regular
                  expressions.

                  If / is the delimiter then the initial 'm' is
                  optional.  With the 'm' you can use any pair of
                  non-alphanumeric characters as delimiters.  This is
                  particularly useful for matching Unix path names
                  that contain '/'.  If the final delimiter is
                  followed by the optional letter 'i', the matching is
                  done in a case-insensitive manner.  PATTERN may
                  contain references to scalar variables, which will
                  be interpolated (and the pattern recompiled) every
                  time the pattern search is evaluated.  (Note that $)
                  and $| may not be interpolated because they look
                  like end-of-string tests.)  If you want such a
                  pattern to be compiled only once, add an "o" after
                  the trailing delimiter.  This avoids expensive run-
                  time recompilations, and is useful when the value
                  you are interpolating won't change over the life of
                  the script.  If the PATTERN evaluates to a null
                  string, the most recent successful regular
                  expression is used instead.

                  If used in a context that requires an array value, a
                  pattern match returns an array consisting of the
                  subexpressions matched by the parentheses in the
                  pattern, i.e. ($1, $2, $3...).  It does NOT actually



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                  set $1, $2, etc. in this case, nor does it set $+,
                  $`, $& or $'.  If the match fails, a null array is
                  returned.  If the match succeeds, but there were no
                  parentheses, an array value of (1) is returned.

                  Examples:

                      open(tty, '/dev/tty');
                      <tty> =~ /^y/i && do foo();    # do foo if desired

                      if (/Version: *([0-9.]*)/) { $version = $1; }

                      next if m#^/usr/spool/uucp#;

                      # poor man's grep
                      $arg = shift;
                      while (<>) {
                           print if /$arg/o;    # compile only once
                      }

                      if (($F1, $F2, $Etc) = ($foo =~ /^(\S+)\s+(\S+)\s*(.*)/))

                  This last example splits $foo into the first two
                  words and the remainder of the line, and assigns
                  those three fields to $F1, $F2 and $Etc.  The
                  conditional is true if any variables were assigned,
                  i.e. if the pattern matched.

                  The "g" modifier specifies global pattern
                  matching--that is, matching as many times as
                  possible within the string.  How it behaves depends
                  on the context.  In an array context, it returns a
                  list of all the substrings matched by all the
                  parentheses in the regular expression.  If there are
                  no parentheses, it returns a list of all the matched
                  strings, as if there were parentheses around the
                  whole pattern.  In a scalar context, it iterates
                  through the string, returning TRUE each time it
                  matches, and FALSE when it eventually runs out of
                  matches.  (In other words, it remembers where it
                  left off last time and restarts the search at that
                  point.)  It presumes that you have not modified the
                  string since the last match.  Modifying the string
                  between matches may result in undefined behavior.
                  (You can actually get away with in-place
                  modifications via substr() that do not change the
                  length of the entire string.  In general, however,
                  you should be using s///g for such modifications.)
                  Examples:

                       # array context
                       ($one,$five,$fifteen) = (`uptime` =~ /(\d+\.\d+)/g);



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                       # scalar context
                       $/ = ""; $* = 1;
                       while ($paragraph = <>) {
                           while ($paragraph =~ /[a-z]['")]*[.!?]+['")]*\s/g) {
                            $sentences++;
                           }
                       }
                       print "$sentences\n";


          mkdir(FILENAME,MODE)
                  Creates the directory specified by FILENAME, with
                  permissions specified by MODE (as modified by
                  umask).  If it succeeds it returns 1, otherwise it
                  returns 0 and sets $! (errno).

          msgctl(ID,CMD,ARG)
                  Calls the System V IPC function msgctl.  If CMD is
                  &IPC_STAT, then ARG must be a variable which will
                  hold the returned msqid_ds structure.  Returns like
                  ioctl: the undefined value for error, "0 but true"
                  for zero, or the actual return value otherwise.

          msgget(KEY,FLAGS)
                  Calls the System V IPC function msgget.  Returns the
                  message queue id, or the undefined value if there is
                  an error.

          msgsnd(ID,MSG,FLAGS)
                  Calls the System V IPC function msgsnd to send the
                  message MSG to the message queue ID.  MSG must begin
                  with the long integer message type, which may be
                  created with pack("L", $type).  Returns true if
                  successful, or false if there is an error.

          msgrcv(ID,VAR,SIZE,TYPE,FLAGS)
                  Calls the System V IPC function msgrcv to receive a
                  message from message queue ID into variable VAR with
                  a maximum message size of SIZE.  Note that if a
                  message is received, the message type will be the
                  first thing in VAR, and the maximum length of VAR is
                  SIZE plus the size of the message type.  Returns
                  true if successful, or false if there is an error.

          next LABEL

          next    The next command is like the continue statement in
                  C; it starts the next iteration of the loop:







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                       line: while (<STDIN>) {
                            next line if /^#/;  # discard comments
                            ...
                       }

                  Note that if there were a continue block on the
                  above, it would get executed even on discarded
                  lines.  If the LABEL is omitted, the command refers
                  to the innermost enclosing loop.

          oct(EXPR)

          oct EXPR
                  Returns the decimal value of EXPR interpreted as an
                  octal string.  (If EXPR happens to start off with
                  0x, interprets it as a hex string instead.)  The
                  following will handle decimal, octal and hex in the
                  standard notation:

                       $val = oct($val) if $val =~ /^0/;

                  If EXPR is omitted, uses $_.

          open(FILEHANDLE,EXPR)

          open(FILEHANDLE)

          open FILEHANDLE
                  Opens the file whose filename is given by EXPR, and
                  associates it with FILEHANDLE.  If FILEHANDLE is an
                  expression, its value is used as the name of the
                  real filehandle wanted.  If EXPR is omitted, the
                  scalar variable of the same name as the FILEHANDLE
                  contains the filename.  If the filename begins with
                  "<" or nothing, the file is opened for input.  If
                  the filename begins with ">", the file is opened for
                  output.  If the filename begins with ">>", the file
                  is opened for appending.  (You can put a '+' in
                  front of the '>' or '<' to indicate that you want
                  both read and write access to the file.)  If the
                  filename begins with "|", the filename is
                  interpreted as a command to which output is to be
                  piped, and if the filename ends with a "|", the
                  filename is interpreted as command which pipes input
                  to us.  (You may not have a command that pipes both
                  in and out.)  Opening '-' opens STDIN and opening
                  '>-' opens STDOUT.  Open returns non-zero upon
                  success, the undefined value otherwise.  If the open
                  involved a pipe, the return value happens to be the
                  pid of the subprocess.  Examples:





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                       $article = 100;
                       open article || die "Can't find article $article: $!\n";
                       while (<article>) {...

                       open(LOG, '>>/usr/spool/news/twitlog');
                                           # (log is reserved)

                       open(article, "caesar <$article |");
                                           # decrypt article

                       open(extract, "|sort >/tmp/Tmp$$");
                                           # $$ is our process#

                       # process argument list of files along with any includes

                       foreach $file (@ARGV) {
                            do process($file, 'fh00');    # no pun intended
                       }

                       sub process {
                            local($filename, $input) = @_;
                            $input++;      # this is a string increment
                            unless (open($input, $filename)) {
                                 print STDERR "Can't open $filename: $!\n";
                                 return;
                            }
                            while (<$input>) {       # note use of indirection
                                 if (/^#include "(.*)"/) {
                                      do process($1, $input);
                                      next;
                                 }
                                 ...       # whatever
                            }
                       }

                  You may also, in the Bourne shell tradition, specify
                  an EXPR beginning with ">&", in which case the rest
                  of the string is interpreted as the name of a
                  filehandle (or file descriptor, if numeric) which is
                  to be duped and opened.  You may use & after >, >>,
                  <, +>, +>> and +<.  The mode you specify should
                  match the mode of the original filehandle.  Here is
                  a script that saves, redirects, and restores STDOUT
                  and STDERR:











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                       #!/usr/bin/perl
                       open(SAVEOUT, ">&STDOUT");
                       open(SAVEERR, ">&STDERR");

                       open(STDOUT, ">foo.out") || die "Can't redirect stdout";
                       open(STDERR, ">&STDOUT") || die "Can't dup stdout";

                       select(STDERR); $| = 1;       # make unbuffered
                       select(STDOUT); $| = 1;       # make unbuffered

                       print STDOUT "stdout 1\n";    # this works for
                       print STDERR "stderr 1\n";    # subprocesses too

                       close(STDOUT);
                       close(STDERR);

                       open(STDOUT, ">&SAVEOUT");
                       open(STDERR, ">&SAVEERR");

                       print STDOUT "stdout 2\n";
                       print STDERR "stderr 2\n";

                  If you open a pipe on the command "-", i.e. either
                  "|-" or "-|", then there is an implicit fork done,
                  and the return value of open is the pid of the child
                  within the parent process, and 0 within the child
                  process.  (Use defined($pid) to determine if the
                  open was successful.)  The filehandle behaves
                  normally for the parent, but i/o to that filehandle
                  is piped from/to the STDOUT/STDIN of the child
                  process.  In the child process the filehandle isn't
                  opened--i/o happens from/to the new STDOUT or STDIN.
                  Typically this is used like the normal piped open
                  when you want to exercise more control over just how
                  the pipe command gets executed, such as when you are
                  running setuid, and don't want to have to scan shell
                  commands for metacharacters.  The following pairs
                  are more or less equivalent:

                       open(FOO, "|tr '[a-z]' '[A-Z]'");
                       open(FOO, "|-") || exec 'tr', '[a-z]', '[A-Z]';

                       open(FOO, "cat -n '$file'|");
                       open(FOO, "-|") || exec 'cat', '-n', $file;

                  Explicitly closing any piped filehandle causes the
                  parent process to wait for the child to finish, and
                  returns the status value in $?.  Note: on any
                  operation which may do a fork, unflushed buffers
                  remain unflushed in both processes, which means you
                  may need to set $| to avoid duplicate output.




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                  The filename that is passed to open will have
                  leading and trailing whitespace deleted.  In order
                  to open a file with arbitrary weird characters in
                  it, it's necessary to protect any leading and
                  trailing whitespace thusly:

                          $file =~ s#^(\s)#./$1#;
                          open(FOO, "< $file\0");


          opendir(DIRHANDLE,EXPR)
                  Opens a directory named EXPR for processing by
                  readdir(), telldir(), seekdir(), rewinddir() and
                  closedir().  Returns true if successful.  DIRHANDLEs
                  have their own namespace separate from FILEHANDLEs.

          ord(EXPR)

          ord EXPR
                  Returns the numeric ascii value of the first
                  character of EXPR.  If EXPR is omitted, uses $_.

          pack(TEMPLATE,LIST)
                  Takes an array or list of values and packs it into a
                  binary structure, returning the string containing
                  the structure.  The TEMPLATE is a sequence of
                  characters that give the order and type of values,
                  as follows:

                       A    An ascii string, will be space padded.
                       a    An ascii string, will be null padded.
                       c    A signed char value.
                       C    An unsigned char value.
                       s    A signed short value.
                       S    An unsigned short value.
                       i    A signed integer value.
                       I    An unsigned integer value.
                       l    A signed long value.
                       L    An unsigned long value.
                       n    A short in "network" order.
                       N    A long in "network" order.
                       f    A single-precision float in the native format.
                       d    A double-precision float in the native format.
                       p    A pointer to a string.
                       v    A short in "VAX" (little-endian) order.
                       V    A long in "VAX" (little-endian) order.
                       x    A null byte.
                       X    Back up a byte.
                       @    Null fill to absolute position.
                       u    A uuencoded string.
                       b    A bit string (ascending bit order, like vec()).
                       B    A bit string (descending bit order).



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                       h    A hex string (low nybble first).
                       H    A hex string (high nybble first).

                  Each letter may optionally be followed by a number
                  which gives a repeat count.  With all types except
                  "a", "A", "b", "B", "h" and "H", the pack function
                  will gobble up that many values from the LIST.  A *
                  for the repeat count means to use however many items
                  are left.  The "a" and "A" types gobble just one
                  value, but pack it as a string of length count,
                  padding with nulls or spaces as necessary.  (When
                  unpacking, "A" strips trailing spaces and nulls, but
                  "a" does not.)  Likewise, the "b" and "B" fields
                  pack a string that many bits long.  The "h" and "H"
                  fields pack a string that many nybbles long.  Real
                  numbers (floats and doubles) are in the native
                  machine format only; due to the multiplicity of
                  floating formats around, and the lack of a standard
                  "network" representation, no facility for
                  interchange has been made.  This means that packed
                  floating point data written on one machine may not
                  be readable on another - even if both use IEEE
                  floating point arithmetic (as the endian-ness of the
                  memory representation is not part of the IEEE spec).
                  Note that perl uses doubles internally for all
                  numeric calculation, and converting from double ->
                  float -> double will lose precision (i.e.
                  unpack("f", pack("f", $foo)) will not in general
                  equal $foo).
                  Examples:

                       $foo = pack("cccc",65,66,67,68);
                       # foo eq "ABCD"
                       $foo = pack("c4",65,66,67,68);
                       # same thing

                       $foo = pack("ccxxcc",65,66,67,68);
                       # foo eq "AB\0\0CD"

                       $foo = pack("s2",1,2);
                       # "\1\0\2\0" on little-endian
                       # "\0\1\0\2" on big-endian

                       $foo = pack("a4","abcd","x","y","z");
                       # "abcd"

                       $foo = pack("aaaa","abcd","x","y","z");
                       # "axyz"

                       $foo = pack("a14","abcdefg");
                       # "abcdefg\0\0\0\0\0\0\0"




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                       $foo = pack("i9pl", gmtime);
                       # a real struct tm (on my system anyway)

                       sub bintodec {
                           unpack("N", pack("B32", substr("0" x 32 . shift, -32)));
                       }
                  The same template may generally also be used in the
                  unpack function.

          pipe(READHANDLE,WRITEHANDLE)
                  Opens a pair of connected pipes like the
                  corresponding system call.  Note that if you set up
                  a loop of piped processes, deadlock can occur unless
                  you are very careful.  In addition, note that perl's
                  pipes use stdio buffering, so you may need to set $|
                  to flush your WRITEHANDLE after each command,
                  depending on the application.  [Requires version 3.0
                  patchlevel 9.]

          pop(ARRAY)

          pop ARRAY
                  Pops and returns the last value of the array,
                  shortening the array by 1.  Has the same effect as

                       $tmp = $ARRAY[$#ARRAY--];

                  If there are no elements in the array, returns the
                  undefined value.

          print(FILEHANDLE LIST)

          print(LIST)

          print FILEHANDLE LIST

          print LIST

          print   Prints a string or a comma-separated list of
                  strings.  Returns non-zero if successful.
                  FILEHANDLE may be a scalar variable name, in which
                  case the variable contains the name of the
                  filehandle, thus introducing one level of
                  indirection.  (NOTE: If FILEHANDLE is a variable and
                  the next token is a term, it may be misinterpreted
                  as an operator unless you interpose a + or put
                  parens around the arguments.)  If FILEHANDLE is
                  omitted, prints by default to standard output (or to
                  the last selected output channel--see select()).  If
                  LIST is also omitted, prints $_ to STDOUT.  To set
                  the default output channel to something other than
                  STDOUT use the select operation.  Note that, because



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                  print takes a LIST, anything in the LIST is
                  evaluated in an array context, and any subroutine
                  that you call will have one or more of its
                  expressions evaluated in an array context.  Also be
                  careful not to follow the print keyword with a left
                  parenthesis unless you want the corresponding right
                  parenthesis to terminate the arguments to the
                  print--interpose a + or put parens around all the
                  arguments.

          printf(FILEHANDLE LIST)

          printf(LIST)

          printf FILEHANDLE LIST

          printf LIST
                  Equivalent to a "print FILEHANDLE sprintf(LIST)".

          push(ARRAY,LIST)
                  Treats ARRAY (@ is optional) as a stack, and pushes
                  the values of LIST onto the end of ARRAY.  The
                  length of ARRAY increases by the length of LIST.
                  Has the same effect as

                      for $value (LIST) {
                           $ARRAY[++$#ARRAY] = $value;
                      }

                  but is more efficient.

          q/STRING/

          qq/STRING/

          qx/STRING/
                  These are not really functions, but simply syntactic
                  sugar to let you avoid putting too many backslashes
                  into quoted strings.  The q operator is a
                  generalized single quote, and the qq operator a
                  generalized double quote.  The qx operator is a
                  generalized backquote.  Any non-alphanumeric
                  delimiter can be used in place of /, including
                  newline.  If the delimiter is an opening bracket or
                  parenthesis, the final delimiter will be the
                  corresponding closing bracket or parenthesis.
                  (Embedded occurrences of the closing bracket need to
                  be backslashed as usual.)  Examples:







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                       $foo = q!I said, "You said, 'She said it.'"!;
                       $bar = q('This is it.');
                       $today = qx{ date };
                       $_ .= qq
                  *** The previous line contains the naughty word "$&".\n
                            if /(ibm|apple|awk)/;      # :-)


          rand(EXPR)

          rand EXPR

          rand    Returns a random fractional number between 0 and the
                  value of EXPR.  (EXPR should be positive.)  If EXPR
                  is omitted, returns a value between 0 and 1.  See
                  also srand().

          read(FILEHANDLE,SCALAR,LENGTH,OFFSET)

          read(FILEHANDLE,SCALAR,LENGTH)
                  Attempts to read LENGTH bytes of data into variable
                  SCALAR from the specified FILEHANDLE.  Returns the
                  number of bytes actually read, or undef if there was
                  an error.  SCALAR will be grown or shrunk to the
                  length actually read.  An OFFSET may be specified to
                  place the read data at some other place than the
                  beginning of the string.  This call is actually
                  implemented in terms of stdio's fread call.  To get
                  a true read system call, see sysread.

          readdir(DIRHANDLE)

          readdir DIRHANDLE
                  Returns the next directory entry for a directory
                  opened by opendir().  If used in an array context,
                  returns all the rest of the entries in the
                  directory.  If there are no more entries, returns an
                  undefined value in a scalar context or a null list
                  in an array context.

          readlink(EXPR)

          readlink EXPR
                  Returns the value of a symbolic link, if symbolic
                  links are implemented.  If not, gives a fatal error.
                  If there is some system error, returns the undefined
                  value and sets $! (errno).  If EXPR is omitted, uses
                  $_.

          recv(SOCKET,SCALAR,LEN,FLAGS)
                  Receives a message on a socket.  Attempts to receive
                  LENGTH bytes of data into variable SCALAR from the



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                  specified SOCKET filehandle.  Returns the address of
                  the sender, or the undefined value if there's an
                  error.  SCALAR will be grown or shrunk to the length
                  actually read.  Takes the same flags as the system
                  call of the same name.

          redo LABEL

          redo    The redo command restarts the loop block without
                  evaluating the conditional again.  The continue
                  block, if any, is not executed.  If the LABEL is
                  omitted, the command refers to the innermost
                  enclosing loop.  This command is normally used by
                  programs that want to lie to themselves about what
                  was just input:

                       # a simpleminded Pascal comment stripper
                       # (warning: assumes no { or } in strings)
                       line: while (<STDIN>) {
                            while (s|({.*}.*){.*}|$1 |) {}
                            s|{.*}| |;
                            if (s|{.*| |) {
                                 $front = $_;
                                 while (<STDIN>) {
                                      if (/}/) {     # end of comment?
                                           s|^|$front{|;
                                           redo line;
                                      }
                                 }
                            }
                            print;
                       }


          rename(OLDNAME,NEWNAME)
                  Changes the name of a file.  Returns 1 for success,
                  0 otherwise.  Will not work across filesystem
                  boundaries.

          require(EXPR)

          require EXPR

          require Includes the library file specified by EXPR, or by
                  $_ if EXPR is not supplied.  Has semantics similar
                  to the following subroutine:

                       sub require {
                           local($filename) = @_;
                           return 1 if $INC{$filename};
                           local($realfilename,$result);
                           ITER: {



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                            foreach $prefix (@INC) {
                                $realfilename = "$prefix/$filename";
                                if (-f $realfilename) {
                                 $result = do $realfilename;
                                 last ITER;
                                }
                            }
                            die "Can't find $filename in \@INC";
                           }
                           die $@ if $@;
                           die "$filename did not return true value" unless $result;
                           $INC{$filename} = $realfilename;
                           $result;
                       }

                  Note that the file will not be included twice under
                  the same specified name.  The file must return true
                  as the last statement to indicate successful
                  execution of any initialization code, so it's
                  customary to end such a file with "1;" unless you're
                  sure it'll return true otherwise.

          reset(EXPR)

          reset EXPR

          reset   Generally used in a continue block at the end of a
                  loop to clear variables and reset ?? searches so
                  that they work again.  The expression is interpreted
                  as a list of single characters (hyphens allowed for
                  ranges).  All variables and arrays beginning with
                  one of those letters are reset to their pristine
                  state.  If the expression is omitted, one-match
                  searches (?pattern?) are reset to match again.  Only
                  resets variables or searches in the current package.
                  Always returns 1.  Examples:

                      reset 'X';      # reset all X variables
                      reset 'a-z';    # reset lower case variables
                      reset;          # just reset ?? searches

                  Note: resetting "A-Z" is not recommended since
                  you'll wipe out your ARGV and ENV arrays.

                  The use of reset on dbm associative arrays does not
                  change the dbm file.  (It does, however, flush any
                  entries cached by perl, which may be useful if you
                  are sharing the dbm file.  Then again, maybe not.)

          return LIST
                  Returns from a subroutine with the value specified.
                  (Note that a subroutine can automatically return the



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                  value of the last expression evaluated.  That's the
                  preferred method--use of an explicit return is a bit
                  slower.)

          reverse(LIST)

          reverse LIST
                  In an array context, returns an array value
                  consisting of the elements of LIST in the opposite
                  order.  In a scalar context, returns a string value
                  consisting of the bytes of the first element of LIST
                  in the opposite order.

          rewinddir(DIRHANDLE)

          rewinddir DIRHANDLE
                  Sets the current position to the beginning of the
                  directory for the readdir() routine on DIRHANDLE.

          rindex(STR,SUBSTR,POSITION)

          rindex(STR,SUBSTR)
                  Works just like index except that it returns the
                  position of the LAST occurrence of SUBSTR in STR.
                  If POSITION is specified, returns the last
                  occurrence at or before that position.

          rmdir(FILENAME)

          rmdir FILENAME
                  Deletes the directory specified by FILENAME if it is
                  empty.  If it succeeds it returns 1, otherwise it
                  returns 0 and sets $! (errno).  If FILENAME is
                  omitted, uses $_.

          s/PATTERN/REPLACEMENT/gieo
                  Searches a string for a pattern, and if found,
                  replaces that pattern with the replacement text and
                  returns the number of substitutions made.  Otherwise
                  it returns false (0).  The "g" is optional, and if
                  present, indicates that all occurrences of the
                  pattern are to be replaced.  The "i" is also
                  optional, and if present, indicates that matching is
                  to be done in a case-insensitive manner.  The "e" is
                  likewise optional, and if present, indicates that
                  the replacement string is to be evaluated as an
                  expression rather than just as a double-quoted
                  string.  Any non-alphanumeric delimiter may replace
                  the slashes; if single quotes are used, no
                  interpretation is done on the replacement string
                  (the e modifier overrides this, however); if
                  backquotes are used, the replacement string is a



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                  command to execute whose output will be used as the
                  actual replacement text.  If the PATTERN is
                  delimited by bracketing quotes, the REPLACEMENT has
                  its own pair of quotes, which may or may not be
                  bracketing quotes, e.g.  s(foo)(bar) or s<foo>/bar/.
                  If no string is specified via the =~ or !~ operator,
                  the $_ string is searched and modified.  (The string
                  specified with =~ must be a scalar variable, an
                  array element, or an assignment to one of those,
                  i.e. an lvalue.)  If the pattern contains a $ that
                  looks like a variable rather than an end-of-string
                  test, the variable will be interpolated into the
                  pattern at run-time.  If you only want the pattern
                  compiled once the first time the variable is
                  interpolated, add an "o" at the end.  If the PATTERN
                  evaluates to a null string, the most recent
                  successful regular expression is used instead.  See
                  also the section on regular expressions.  Examples:

                      s/\bgreen\b/mauve/g;      # don't change wintergreen

                      $path =~ s|/usr/bin|/usr/local/bin|;

                      s/Login: $foo/Login: $bar/; # run-time pattern

                      ($foo = $bar) =~ s/bar/foo/;

                      $_ = 'abc123xyz';
                      s/\d+/$&*2/e;        # yields 'abc246xyz'
                      s/\d+/sprintf("%5d",$&)/e;     # yields 'abc  246xyz'
                      s/\w/$& x 2/eg;      # yields 'aabbcc  224466xxyyzz'

                      s/([^ ]*) *([^ ]*)/$2 $1/;     # reverse 1st two fields

                  (Note the use of $ instead of \ in the last example.
                  See section on regular expressions.)

          scalar(EXPR)
                  Forces EXPR to be interpreted in a scalar context
                  and returns the value of EXPR.

          seek(FILEHANDLE,POSITION,WHENCE)
                  Randomly positions the file pointer for FILEHANDLE,
                  just like the fseek() call of stdio.  FILEHANDLE may
                  be an expression whose value gives the name of the
                  filehandle.  Returns 1 upon success, 0 otherwise.

          seekdir(DIRHANDLE,POS)
                  Sets the current position for the readdir() routine
                  on DIRHANDLE.  POS must be a value returned by
                  telldir().  Has the same caveats about possible
                  directory compaction as the corresponding system



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                  library routine.

          select(FILEHANDLE)

          select  Returns the currently selected filehandle.  Sets the
                  current default filehandle for output, if FILEHANDLE
                  is supplied.  This has two effects: first, a write
                  or a print without a filehandle will default to this
                  FILEHANDLE.  Second, references to variables related
                  to output will refer to this output channel.  For
                  example, if you have to set the top of form format
                  for more than one output channel, you might do the
                  following:

                       select(REPORT1);
                       $^ = 'report1_top';
                       select(REPORT2);
                       $^ = 'report2_top';

                  FILEHANDLE may be an expression whose value gives
                  the name of the actual filehandle.  Thus:

                       $oldfh = select(STDERR); $| = 1; select($oldfh);


          select(RBITS,WBITS,EBITS,TIMEOUT)
                  This calls the select system call with the bitmasks
                  specified, which can be constructed using fileno()
                  and vec(), along these lines:

                       $rin = $win = $ein = '';
                       vec($rin,fileno(STDIN),1) = 1;
                       vec($win,fileno(STDOUT),1) = 1;
                       $ein = $rin | $win;

                  If you want to select on many filehandles you might
                  wish to write a subroutine:

                       sub fhbits {
                           local(@fhlist) = split(' ',$_[0]);
                           local($bits);
                           for (@fhlist) {
                            vec($bits,fileno($_),1) = 1;
                           }
                           $bits;
                       }
                       $rin = &fhbits('STDIN TTY SOCK');

                  The usual idiom is:

                       ($nfound,$timeleft) =
                         select($rout=$rin, $wout=$win, $eout=$ein, $timeout);



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                  or to block until something becomes ready:

                       $nfound = select($rout=$rin, $wout=$win,
                                      $eout=$ein, undef);

                  Any of the bitmasks can also be undef.  The timeout,
                  if specified, is in seconds, which may be
                  fractional.  NOTE: not all implementations are
                  capable of returning the $timeleft.  If not, they
                  always return $timeleft equal to the supplied
                  $timeout.

          semctl(ID,SEMNUM,CMD,ARG)
                  Calls the System V IPC function semctl.  If CMD is
                  &IPC_STAT or &GETALL, then ARG must be a variable
                  which will hold the returned semid_ds structure or
                  semaphore value array.  Returns like ioctl: the
                  undefined value for error, "0 but true" for zero, or
                  the actual return value otherwise.

          semget(KEY,NSEMS,SIZE,FLAGS)
                  Calls the System V IPC function semget.  Returns the
                  semaphore id, or the undefined value if there is an
                  error.

          semop(KEY,OPSTRING)
                  Calls the System V IPC function semop to perform
                  semaphore operations such as signaling and waiting.
                  OPSTRING must be a packed array of semop structures.
                  Each semop structure can be generated with
                  'pack("sss", $semnum, $semop, $semflag)'.  The
                  number of semaphore operations is implied by the
                  length of OPSTRING.  Returns true if successful, or
                  false if there is an error.  As an example, the
                  following code waits on semaphore $semnum of
                  semaphore id $semid:

                       $semop = pack("sss", $semnum, -1, 0);
                       die "Semaphore trouble: $!\n" unless semop($semid, $semop);

                  To signal the semaphore, replace "-1" with "1".

          send(SOCKET,MSG,FLAGS,TO)

          send(SOCKET,MSG,FLAGS)
                  Sends a message on a socket.  Takes the same flags
                  as the system call of the same name.  On unconnected
                  sockets you must specify a destination to send TO.
                  Returns the number of characters sent, or the
                  undefined value if there is an error.





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          setpgrp(PID,PGRP)
                  Sets the current process group for the specified
                  PID, 0 for the current process.  Will produce a
                  fatal error if used on a machine that doesn't
                  implement setpgrp(2).

          setpriority(WHICH,WHO,PRIORITY)
                  Sets the current priority for a process, a process
                  group, or a user.  (See setpriority(2).)  Will
                  produce a fatal error if used on a machine that
                  doesn't implement setpriority(2).

          setsockopt(SOCKET,LEVEL,OPTNAME,OPTVAL)
                  Sets the socket option requested.  Returns undefined
                  if there is an error.  OPTVAL may be specified as
                  undef if you don't want to pass an argument.

          shift(ARRAY)

          shift ARRAY

          shift   Shifts the first value of the array off and returns
                  it, shortening the array by 1 and moving everything
                  down.  If there are no elements in the array,
                  returns the undefined value.  If ARRAY is omitted,
                  shifts the @ARGV array in the main program, and the
                  @_ array in subroutines.  (This is determined
                  lexically.)  See also unshift(), push() and pop().
                  Shift() and unshift() do the same thing to the left
                  end of an array that push() and pop() do to the
                  right end.

          shmctl(ID,CMD,ARG)
                  Calls the System V IPC function shmctl.  If CMD is
                  &IPC_STAT, then ARG must be a variable which will
                  hold the returned shmid_ds structure.  Returns like
                  ioctl: the undefined value for error, "0 but true"
                  for zero, or the actual return value otherwise.

          shmget(KEY,SIZE,FLAGS)
                  Calls the System V IPC function shmget.  Returns the
                  shared memory segment id, or the undefined value if
                  there is an error.

          shmread(ID,VAR,POS,SIZE)

          shmwrite(ID,STRING,POS,SIZE)
                  Reads or writes the System V shared memory segment
                  ID starting at position POS for size SIZE by
                  attaching to it, copying in/out, and detaching from
                  it.  When reading, VAR must be a variable which will
                  hold the data read.  When writing, if STRING is too



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                  long, only SIZE bytes are used; if STRING is too
                  short, nulls are written to fill out SIZE bytes.
                  Return true if successful, or false if there is an
                  error.

          shutdown(SOCKET,HOW)
                  Shuts down a socket connection in the manner
                  indicated by HOW, which has the same interpretation
                  as in the system call of the same name.

          sin(EXPR)

          sin EXPR
                  Returns the sine of EXPR (expressed in radians).  If
                  EXPR is omitted, returns sine of $_.

          sleep(EXPR)

          sleep EXPR

          sleep   Causes the script to sleep for EXPR seconds, or
                  forever if no EXPR.  May be interrupted by sending
                  the process a SIGALRM.  Returns the number of
                  seconds actually slept.  You probably cannot mix
                  alarm() and sleep() calls, since sleep() is often
                  implemented using alarm().

          socket(SOCKET,DOMAIN,TYPE,PROTOCOL)
                  Opens a socket of the specified kind and attaches it
                  to filehandle SOCKET.  DOMAIN, TYPE and PROTOCOL are
                  specified the same as for the system call of the
                  same name.  You may need to run h2ph on sys/socket.h
                  to get the proper values handy in a perl library
                  file.  Return true if successful.  See the example
                  in the section on Interprocess Communication.

          socketpair(SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL)
                  Creates an unnamed pair of sockets in the specified
                  domain, of the specified type.  DOMAIN, TYPE and
                  PROTOCOL are specified the same as for the system
                  call of the same name.  If unimplemented, yields a
                  fatal error.  Return true if successful.

          sort(SUBROUTINE LIST)

          sort(LIST)

          sort SUBROUTINE LIST

          sort BLOCK LIST





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          sort LIST
                  Sorts the LIST and returns the sorted array value.
                  Nonexistent values of arrays are stripped out.  If
                  SUBROUTINE or BLOCK is omitted, sorts in standard
                  string comparison order.  If SUBROUTINE is
                  specified, gives the name of a subroutine that
                  returns an integer less than, equal to, or greater
                  than 0, depending on how the elements of the array
                  are to be ordered.  (The <=> and cmp operators are
                  extremely useful in such routines.)  SUBROUTINE may
                  be a scalar variable name, in which case the value
                  provides the name of the subroutine to use.  In
                  place of a SUBROUTINE name, you can provide a BLOCK
                  as an anonymous, in-line sort subroutine.

                  In the interests of efficiency the normal calling
                  code for subroutines is bypassed, with the following
                  effects: the subroutine may not be a recursive
                  subroutine, and the two elements to be compared are
                  passed into the subroutine not via @_ but as $a and
                  $b (see example below).  They are passed by
                  reference so don't modify $a and $b.

                  Examples:

                       # sort lexically
                       @articles = sort @files;

                       # same thing, but with explicit sort routine
                       @articles = sort {$a cmp $b} @files;

                       # same thing in reversed order
                       @articles = sort {$b cmp $a} @files;

                       # sort numerically ascending
                       @articles = sort {$a <=> $b} @files;

                       # sort numerically descending
                       @articles = sort {$b <=> $a} @files;

                       # sort using explicit subroutine name
                       sub byage {
                           $age{$a} <=> $age{$b};    # presuming integers
                       }
                       @sortedclass = sort byage @class;










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                       sub reverse { $b cmp $a; }
                       @harry = ('dog','cat','x','Cain','Abel');
                       @george = ('gone','chased','yz','Punished','Axed');
                       print sort @harry;
                            # prints AbelCaincatdogx
                       print sort reverse @harry;
                            # prints xdogcatCainAbel
                       print sort @george, 'to', @harry;
                            # prints AbelAxedCainPunishedcatchaseddoggonetoxyz


          splice(ARRAY,OFFSET,LENGTH,LIST)

          splice(ARRAY,OFFSET,LENGTH)

          splice(ARRAY,OFFSET)
                  Removes the elements designated by OFFSET and LENGTH
                  from an array, and replaces them with the elements
                  of LIST, if any.  Returns the elements removed from
                  the array.  The array grows or shrinks as necessary.
                  If LENGTH is omitted, removes everything from OFFSET
                  onward.  The following equivalencies hold (assuming
                  $[ == 0):

                       push(@a,$x,$y)                splice(@a,$#a+1,0,$x,$y)
                       pop(@a)                       splice(@a,-1)
                       shift(@a)                     splice(@a,0,1)
                       unshift(@a,$x,$y)             splice(@a,0,0,$x,$y)
                       $a[$x] = $y                   splice(@a,$x,1,$y);

                  Example, assuming array lengths are passed before arrays:

                       sub aeq { # compare two array values
                            local(@a) = splice(@_,0,shift);
                            local(@b) = splice(@_,0,shift);
                            return 0 unless @a == @b;     # same len?
                            while (@a) {
                                return 0 if pop(@a) ne pop(@b);
                            }
                            return 1;
                       }
                       if (&aeq($len,@foo[1..$len],0+@bar,@bar)) { ... }


          split(/PATTERN/,EXPR,LIMIT)










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          split(/PATTERN/,EXPR)

          split(/PATTERN/)

          split   Splits a string into an array of strings, and
                  returns it.  (If not in an array context, returns
                  the number of fields found and splits into the @_
                  array.  (In an array context, you can force the
                  split into @_ by using ?? as the pattern delimiters,
                  but it still returns the array value.))  If EXPR is
                  omitted, splits the $_ string.  If PATTERN is also
                  omitted, splits on whitespace (/[ \t\n]+/).
                  Anything matching PATTERN is taken to be a delimiter
                  separating the fields.  (Note that the delimiter may
                  be longer than one character.)  If LIMIT is
                  specified, splits into no more than that many fields
                  (though it may split into fewer).  If LIMIT is
                  unspecified, trailing null fields are stripped
                  (which potential users of pop() would do well to
                  remember).  A pattern matching the null string (not
                  to be confused with a null pattern //, which is just
                  one member of the set of patterns matching a null
                  string) will split the value of EXPR into separate
                  characters at each point it matches that way.  For
                  example:

                       print join(':', split(/ */, 'hi there'));

                  produces the output 'h:i:t:h:e:r:e'.

                  The LIMIT parameter can be used to partially split a
                  line

                       ($login, $passwd, $remainder) = split(/:/, $_, 3);

                  (When assigning to a list, if LIMIT is omitted, perl
                  supplies a LIMIT one larger than the number of
                  variables in the list, to avoid unnecessary work.
                  For the list above LIMIT would have been 4 by
                  default.  In time critical applications it behooves
                  you not to split into more fields than you really
                  need.)

                  If the PATTERN contains parentheses, additional
                  array elements are created from each matching
                  substring in the delimiter.

                       split(/([,-])/,"1-10,20");

                  produces the array value

                       (1,'-',10,',',20)



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                  The pattern /PATTERN/ may be replaced with an
                  expression to specify patterns that vary at runtime.
                  (To do runtime compilation only once, use
                  /$variable/o.)  As a special case, specifying a
                  space (' ') will split on white space just as split
                  with no arguments does, but leading white space does
                  NOT produce a null first field.  Thus, split(' ')
                  can be used to emulate awk's default behavior,
                  whereas split(/ /) will give you as many null
                  initial fields as there are leading spaces.

                  Example:

                       open(passwd, '/etc/passwd');
                       while (<passwd>) {
                            ($login, $passwd, $uid, $gid, $gcos, $home, $shell)
                                 = split(/:/);
                            ...
                       }

                  (Note that $shell above will still have a newline on
                  it.  See chop().)  See also join.

          sprintf(FORMAT,LIST)
                  Returns a string formatted by the usual printf
                  conventions.  The * character is not supported.

          sqrt(EXPR)

          sqrt EXPR
                  Return the square root of EXPR.  If EXPR is omitted,
                  returns square root of $_.

          srand(EXPR)

          srand EXPR
                  Sets the random number seed for the rand operator.
                  If EXPR is omitted, does srand(time).

          stat(FILEHANDLE)

          stat FILEHANDLE

          stat(EXPR)

          stat SCALARVARIABLE
                  Returns a 13-element array giving the statistics for
                  a file, either the file opened via FILEHANDLE, or
                  named by EXPR.  Returns a null list if the stat
                  fails.  Typically used as follows:





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                      ($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size,
                         $atime,$mtime,$ctime,$blksize,$blocks)
                             = stat($filename);

                  If stat is passed the special filehandle consisting
                  of an underline, no stat is done, but the current
                  contents of the stat structure from the last stat or
                  filetest are returned.  Example:

                       if (-x $file && (($d) = stat(_)) && $d < 0) {
                            print "$file is executable NFS file\n";
                       }

                  (This only works on machines for which the device
                  number is negative under NFS.)

          study(SCALAR)

          study SCALAR

          study   Takes extra time to study SCALAR ($_ if unspecified)
                  in anticipation of doing many pattern matches on the
                  string before it is next modified.  This may or may
                  not save time, depending on the nature and number of
                  patterns you are searching on, and on the
                  distribution of character frequencies in the string
                  to be searched--you probably want to compare
                  runtimes with and without it to see which runs
                  faster.  Those loops which scan for many short
                  constant strings (including the constant parts of
                  more complex patterns) will benefit most.  You may
                  have only one study active at a time--if you study a
                  different scalar the first is "unstudied".  (The way
                  study works is this: a linked list of every
                  character in the string to be searched is made, so
                  we know, for example, where all the 'k' characters
                  are.  From each search string, the rarest character
                  is selected, based on some static frequency tables
                  constructed from some C programs and English text.
                  Only those places that contain this "rarest"
                  character are examined.)

                  For example, here is a loop which inserts index
                  producing entries before any line containing a
                  certain pattern:










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                       while (<>) {
                            study;
                            print ".IX foo\n" if /\bfoo\b/;
                            print ".IX bar\n" if /\bbar\b/;
                            print ".IX blurfl\n" if /\bblurfl\b/;
                            ...
                            print;
                       }

                  In searching for /\bfoo\b/, only those locations in
                  $_ that contain 'f' will be looked at, because 'f'
                  is rarer than 'o'.  In general, this is a big win
                  except in pathological cases.  The only question is
                  whether it saves you more time than it took to build
                  the linked list in the first place.

                  Note that if you have to look for strings that you
                  don't know till runtime, you can build an entire
                  loop as a string and eval that to avoid recompiling
                  all your patterns all the time.  Together with
                  undefining $/ to input entire files as one record,
                  this can be very fast, often faster than specialized
                  programs like fgrep.  The following scans a list of
                  files (@files) for a list of words (@words), and
                  prints out the names of those files that contain a
                  match:

                       $search = 'while (<>) { study;';
                       foreach $word (@words) {
                           $search .= "++\$seen{\$ARGV} if /\\b$word\\b/;\n";
                       }
                       $search .= "}";
                       @ARGV = @files;
                       undef $/;
                       eval $search;       # this screams
                       $/ = "\n";          # put back to normal input delim
                       foreach $file (sort keys(%seen)) {
                           print $file, "\n";
                       }


          substr(EXPR,OFFSET,LEN)

          substr(EXPR,OFFSET)
                  Extracts a substring out of EXPR and returns it.
                  First character is at offset 0, or whatever you've
                  set $[ to.  If OFFSET is negative, starts that far
                  from the end of the string.  If LEN is omitted,
                  returns everything to the end of the string.  You
                  can use the substr() function as an lvalue, in which
                  case EXPR must be an lvalue.  If you assign
                  something shorter than LEN, the string will shrink,



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                  and if you assign something longer than LEN, the
                  string will grow to accommodate it.  To keep the
                  string the same length you may need to pad or chop
                  your value using sprintf().

          symlink(OLDFILE,NEWFILE)
                  Creates a new filename symbolically linked to the
                  old filename.  Returns 1 for success, 0 otherwise.
                  On systems that don't support symbolic links,
                  produces a fatal error at run time.  To check for
                  that, use eval:

                       $symlink_exists = (eval 'symlink("","");', $@ eq '');


          syscall(LIST)

          syscall LIST
                  Calls the system call specified as the first element
                  of the list, passing the remaining elements as
                  arguments to the system call.  If unimplemented,
                  produces a fatal error.  The arguments are
                  interpreted as follows: if a given argument is
                  numeric, the argument is passed as an int.  If not,
                  the pointer to the string value is passed.  You are
                  responsible to make sure a string is pre-extended
                  long enough to receive any result that might be
                  written into a string.  If your integer arguments
                  are not literals and have never been interpreted in
                  a numeric context, you may need to add 0 to them to
                  force them to look like numbers.

                       require 'syscall.ph';         # may need to run h2ph
                       syscall(&SYS_write, fileno(STDOUT), "hi there\n", 9);


          sysread(FILEHANDLE,SCALAR,LENGTH,OFFSET)

          sysread(FILEHANDLE,SCALAR,LENGTH)
                  Attempts to read LENGTH bytes of data into variable
                  SCALAR from the specified FILEHANDLE, using the
                  system call read(2).  It bypasses stdio, so mixing
                  this with other kinds of reads may cause confusion.
                  Returns the number of bytes actually read, or undef
                  if there was an error.  SCALAR will be grown or
                  shrunk to the length actually read.  An OFFSET may
                  be specified to place the read data at some other
                  place than the beginning of the string.







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          system(LIST)

          system LIST
                  Does exactly the same thing as "exec LIST" except
                  that a fork is done first, and the parent process
                  waits for the child process to complete.  Note that
                  argument processing varies depending on the number
                  of arguments.  The return value is the exit status
                  of the program as returned by the wait() call.  To
                  get the actual exit value divide by 256.  See also
                  exec.

          syswrite(FILEHANDLE,SCALAR,LENGTH,OFFSET)

          syswrite(FILEHANDLE,SCALAR,LENGTH)
                  Attempts to write LENGTH bytes of data from variable
                  SCALAR to the specified FILEHANDLE, using the system
                  call write(2).  It bypasses stdio, so mixing this
                  with prints may cause confusion.  Returns the number
                  of bytes actually written, or undef if there was an
                  error.  An OFFSET may be specified to place the read
                  data at some other place than the beginning of the
                  string.

          tell(FILEHANDLE)

          tell FILEHANDLE

          tell    Returns the current file position for FILEHANDLE.
                  FILEHANDLE may be an expression whose value gives
                  the name of the actual filehandle.  If FILEHANDLE is
                  omitted, assumes the file last read.

          telldir(DIRHANDLE)

          telldir DIRHANDLE
                  Returns the current position of the readdir()
                  routines on DIRHANDLE.  Value may be given to
                  seekdir() to access a particular location in a
                  directory.  Has the same caveats about possible
                  directory compaction as the corresponding system
                  library routine.

          time    Returns the number of non-leap seconds since
                  00:00:00 UTC, January 1, 1970.  Suitable for feeding
                  to gmtime() and localtime().

          times   Returns a four-element array giving the user and
                  system times, in seconds, for this process and the
                  children of this process.

                      ($user,$system,$cuser,$csystem) = times;



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          tr/SEARCHLIST/REPLACEMENTLIST/cds

          y/SEARCHLIST/REPLACEMENTLIST/cds
                  Translates all occurrences of the characters found
                  in the search list with the corresponding character
                  in the replacement list.  It returns the number of
                  characters replaced or deleted.  If no string is
                  specified via the =~ or !~ operator, the $_ string
                  is translated.  (The string specified with =~ must
                  be a scalar variable, an array element, or an
                  assignment to one of those, i.e. an lvalue.)  For
                  sed devotees, y is provided as a synonym for tr.  If
                  the SEARCHLIST is delimited by bracketing quotes,
                  the REPLACEMENTLIST has its own pair of quotes,
                  which may or may not be bracketing quotes, e.g.
                  tr[A-Z][a-z] or tr(+-*/)/ABCD/.

                  If the c modifier is specified, the SEARCHLIST
                  character set is complemented.  If the d modifier is
                  specified, any characters specified by SEARCHLIST
                  that are not found in REPLACEMENTLIST are deleted.
                  (Note that this is slightly more flexible than the
                  behavior of some tr programs, which delete anything
                  they find in the SEARCHLIST, period.)  If the s
                  modifier is specified, sequences of characters that
                  were translated to the same character are squashed
                  down to 1 instance of the character.

                  If the d modifier was used, the REPLACEMENTLIST is
                  always interpreted exactly as specified.  Otherwise,
                  if the REPLACEMENTLIST is shorter than the
                  SEARCHLIST, the final character is replicated till
                  it is long enough.  If the REPLACEMENTLIST is null,
                  the SEARCHLIST is replicated.  This latter is useful
                  for counting characters in a class, or for squashing
                  character sequences in a class.

                  Examples:

                      $ARGV[1] =~ y/A-Z/a-z/;   # canonicalize to lower case

                      $cnt = tr/*/*/;           # count the stars in $_

                      $cnt = tr/0-9//;          # count the digits in $_

                      tr/a-zA-Z//s;             # bookkeeper -> bokeper

                      ($HOST = $host) =~ tr/a-z/A-Z/;

                      y/a-zA-Z/ /cs;            # change non-alphas to single space

                      tr/\200-\377/\0-\177/;    # delete 8th bit



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          truncate(FILEHANDLE,LENGTH)

          truncate(EXPR,LENGTH)
                  Truncates the file opened on FILEHANDLE, or named by
                  EXPR, to the specified length.  Produces a fatal
                  error if truncate isn't implemented on your system.

          umask(EXPR)

          umask EXPR

          umask   Sets the umask for the process and returns the old
                  one.  If EXPR is omitted, merely returns current
                  umask.

          undef(EXPR)

          undef EXPR

          undef   Undefines the value of EXPR, which must be an
                  lvalue.  Use only on a scalar value, an entire
                  array, or a subroutine name (using &).  (Undef will
                  probably not do what you expect on most predefined
                  variables or dbm array values.)  Always returns the
                  undefined value.  You can omit the EXPR, in which
                  case nothing is undefined, but you still get an
                  undefined value that you could, for instance, return
                  from a subroutine.  Examples:

                       undef $foo;
                       undef $bar{'blurfl'};
                       undef @ary;
                       undef %assoc;
                       undef &mysub;
                       return (wantarray ? () : undef) if $they_blew_it;


          unlink(LIST)

          unlink LIST
                  Deletes a list of files.  Returns the number of
                  files successfully deleted.

                       $cnt = unlink 'a', 'b', 'c';
                       unlink @goners;
                       unlink <*.bak>;

                  Note: unlink will not delete directories unless you
                  are superuser and the ----UUUU flag is supplied to perl.
                  Even if these conditions are met, be warned that
                  unlinking a directory can inflict damage on your
                  filesystem.  Use rmdir instead.



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          unpack(TEMPLATE,EXPR)
                  Unpack does the reverse of pack: it takes a string
                  representing a structure and expands it out into an
                  array value, returning the array value.  (In a
                  scalar context, it merely returns the first value
                  produced.)  The TEMPLATE has the same format as in
                  the pack function.  Here's a subroutine that does
                  substring:

                       sub substr {
                            local($what,$where,$howmuch) = @_;
                            unpack("x$where a$howmuch", $what);
                       }

                  and then there's

                       sub ord { unpack("c",$_[0]); }

                  In addition, you may prefix a field with a %<number>
                  to indicate that you want a <number>-bit checksum of
                  the items instead of the items themselves.  Default
                  is a 16-bit checksum.  For example, the following
                  computes the same number as the System V sum
                  program:

                       while (<>) {
                           $checksum += unpack("%16C*", $_);
                       }
                       $checksum %= 65536;


          unshift(ARRAY,LIST)
                  Does the opposite of a shift.  Or the opposite of a
                  push, depending on how you look at it.  Prepends
                  list to the front of the array, and returns the
                  number of elements in the new array.

                       unshift(ARGV, '-e') unless $ARGV[0] =~ /^-/;


          utime(LIST)

          utime LIST
                  Changes the access and modification times on each
                  file of a list of files.  The first two elements of
                  the list must be the NUMERICAL access and
                  modification times, in that order.  Returns the
                  number of files successfully changed.  The inode
                  modification time of each file is set to the current
                  time.  Example of a "touch" command:





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                       #!/usr/bin/perl
                       $now = time;
                       utime $now, $now, @ARGV;


          values(ASSOC_ARRAY)

          values ASSOC_ARRAY
                  Returns a normal array consisting of all the values
                  of the named associative array.  The values are
                  returned in an apparently random order, but it is
                  the same order as either the keys() or each()
                  function would produce on the same array.  See also
                  keys() and each().

          vec(EXPR,OFFSET,BITS)
                  Treats a string as a vector of unsigned integers,
                  and returns the value of the bitfield specified.
                  May also be assigned to.  BITS must be a power of
                  two from 1 to 32.

                  Vectors created with vec() can also be manipulated
                  with the logical operators |, & and ^, which will
                  assume a bit vector operation is desired when both
                  operands are strings.  This interpretation is not
                  enabled unless there is at least one vec() in your
                  program, to protect older programs.

                  To transform a bit vector into a string or array of
                  0's and 1's, use these:

                       $bits = unpack("b*", $vector);
                       @bits = split(//, unpack("b*", $vector));

                  If you know the exact length in bits, it can be used
                  in place of the *.

          wait    Waits for a child process to terminate and returns
                  the pid of the deceased process, or -1 if there are
                  no child processes.  The status is returned in $?.

          waitpid(PID,FLAGS)
                  Waits for a particular child process to terminate
                  and returns the pid of the deceased process, or -1
                  if there is no such child process.  The status is
                  returned in $?.  If you say

                       require "sys/wait.h";
                       ...
                       waitpid(-1,&WNOHANG);

                  then you can do a non-blocking wait for any process.



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                  Non-blocking wait is only available on machines
                  supporting either the waitpid (2) or wait4 (2)
                  system calls.  However, waiting for a particular pid
                  with FLAGS of 0 is implemented everywhere.  (Perl
                  emulates the system call by remembering the status
                  values of processes that have exited but have not
                  been harvested by the Perl script yet.)

          wantarray
                  Returns true if the context of the currently
                  executing subroutine is looking for an array value.
                  Returns false if the context is looking for a
                  scalar.

                       return wantarray ? () : undef;


          warn(LIST)

          warn LIST
                  Produces a message on STDERR just like "die", but
                  doesn't exit.

          write(FILEHANDLE)

          write(EXPR)

          write   Writes a formatted record (possibly multi-line) to
                  the specified file, using the format associated with
                  that file.  By default the format for a file is the
                  one having the same name is the filehandle, but the
                  format for the current output channel (see select)
                  may be set explicitly by assigning the name of the
                  format to the $~ variable.

                  Top of form processing is handled automatically: if
                  there is insufficient room on the current page for
                  the formatted record, the page is advanced by
                  writing a form feed, a special top-of-page format is
                  used to format the new page header, and then the
                  record is written.  By default the top-of-page
                  format is the name of the filehandle with "_TOP"
                  appended, but it may be dynamicallly set to the
                  format of your choice by assigning the name to the
                  $^ variable while the filehandle is selected.  The
                  number of lines remaining on the current page is in
                  variable $-, which can be set to 0 to force a new
                  page.

                  If FILEHANDLE is unspecified, output goes to the
                  current default output channel, which starts out as
                  STDOUT but may be changed by the select operator.



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                  If the FILEHANDLE is an EXPR, then the expression is
                  evaluated and the resulting string is used to look
                  up the name of the FILEHANDLE at run time.  For more
                  on formats, see the section on formats later on.

                  Note that write is NOT the opposite of read.

          PPPPrrrreeeecccceeeeddddeeeennnncccceeee

          Perl operators have the following associativity and
          precedence:

          nonassoc  print printf exec system sort reverse
                         chmod chown kill unlink utime die return
          left      ,
          right     = += -= *= etc.
          right     ?:
          nonassoc  ..
          left      ||
          left      &&
          left      | ^
          left      &
          nonassoc  == != <=> eq ne cmp
          nonassoc  < > <= >= lt gt le ge
          nonassoc  chdir exit eval reset sleep rand umask
          nonassoc  -r -w -x etc.
          left      << >>
          left      + - .
          left      * / % x
          left      =~ !~
          right     ! ~ and unary minus
          right     **
          nonassoc  ++ --
          left      '('

          As mentioned earlier, if any list operator (print, etc.) or
          any unary operator (chdir, etc.)  is followed by a left
          parenthesis as the next token on the same line, the operator
          and arguments within parentheses are taken to be of highest
          precedence, just like a normal function call.  Examples:

               chdir $foo || die;       # (chdir $foo) || die
               chdir($foo) || die;      # (chdir $foo) || die
               chdir ($foo) || die;     # (chdir $foo) || die
               chdir +($foo) || die;    # (chdir $foo) || die

          but, because * is higher precedence than ||:

               chdir $foo * 20;         # chdir ($foo * 20)
               chdir($foo) * 20;        # (chdir $foo) * 20
               chdir ($foo) * 20;       # (chdir $foo) * 20
               chdir +($foo) * 20;      # chdir ($foo * 20)



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               rand 10 * 20;            # rand (10 * 20)
               rand(10) * 20;           # (rand 10) * 20
               rand (10) * 20;          # (rand 10) * 20
               rand +(10) * 20;         # rand (10 * 20)

          In the absence of parentheses, the precedence of list
          operators such as print, sort or chmod is either very high
          or very low depending on whether you look at the left side
          of operator or the right side of it.  For example, in

               @ary = (1, 3, sort 4, 2);
               print @ary;         # prints 1324

          the commas on the right of the sort are evaluated before the
          sort, but the commas on the left are evaluated after.  In
          other words, list operators tend to gobble up all the
          arguments that follow them, and then act like a simple term
          with regard to the preceding expression.  Note that you have
          to be careful with parens:

               # These evaluate exit before doing the print:
               print($foo, exit);  # Obviously not what you want.
               print $foo, exit;   # Nor is this.

               # These do the print before evaluating exit:
               (print $foo), exit; # This is what you want.
               print($foo), exit;  # Or this.
               print ($foo), exit; # Or even this.

          Also note that

               print ($foo & 255) + 1, "\n";

          probably doesn't do what you expect at first glance.

          SSSSuuuubbbbrrrroooouuuuttttiiiinnnneeeessss

          A subroutine may be declared as follows:

              sub NAME BLOCK


          Any arguments passed to the routine come in as array @_,
          that is ($_[0], $_[1], ...).  The array @_ is a local array,
          but its values are references to the actual scalar
          parameters.  The return value of the subroutine is the value
          of the last expression evaluated, and can be either an array
          value or a scalar value.  Alternately, a return statement
          may be used to specify the returned value and exit the
          subroutine.  To create local variables see the local
          operator.




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          A subroutine is called using the do operator or the &
          operator.

          Example:

               sub MAX {
                    local($max) = pop(@_);
                    foreach $foo (@_) {
                         $max = $foo if $max < $foo;
                    }
                    $max;
               }

               ...
               $bestday = &MAX($mon,$tue,$wed,$thu,$fri);

          Example:

               # get a line, combining continuation lines
               #  that start with whitespace
               sub get_line {
                    $thisline = $lookahead;
                    line: while ($lookahead = <STDIN>) {
                         if ($lookahead =~ /^[ \t]/) {
                              $thisline .= $lookahead;
                         }
                         else {
                              last line;
                         }
                    }
                    $thisline;
               }

               $lookahead = <STDIN>;    # get first line
               while ($_ = do get_line()) {
                    ...
               }

          Use array assignment to a local list to name your formal arguments:

               sub maybeset {
                    local($key, $value) = @_;
                    $foo{$key} = $value unless $foo{$key};
               }

          This also has the effect of turning call-by-reference into
          call-by-value, since the assignment copies the values.

          Subroutines may be called recursively.  If a subroutine is
          called using the & form, the argument list is optional.  If
          omitted, no @_ array is set up for the subroutine; the @_
          array at the time of the call is visible to subroutine



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          instead.

               do foo(1,2,3);      # pass three arguments
               &foo(1,2,3);        # the same

               do foo();      # pass a null list
               &foo();             # the same
               &foo;               # pass no arguments--more efficient


          PPPPaaaassssssssiiiinnnngggg BBBByyyy RRRReeeeffffeeeerrrreeeennnncccceeee

          Sometimes you don't want to pass the value of an array to a
          subroutine but rather the name of it, so that the subroutine
          can modify the global copy of it rather than working with a
          local copy.  In perl you can refer to all the objects of a
          particular name by prefixing the name with a star: *foo.
          When evaluated, it produces a scalar value that represents
          all the objects of that name, including any filehandle,
          format or subroutine.  When assigned to within a local()
          operation, it causes the name mentioned to refer to whatever
          * value was assigned to it.  Example:

               sub doubleary {
                   local(*someary) = @_;
                   foreach $elem (@someary) {
                    $elem *= 2;
                   }
               }
               do doubleary(*foo);
               do doubleary(*bar);

          Assignment to *name is currently recommended only inside a
          local().  You can actually assign to *name anywhere, but the
          previous referent of *name may be stranded forever.  This
          may or may not bother you.

          Note that scalars are already passed by reference, so you
          can modify scalar arguments without using this mechanism by
          referring explicitly to the $_[nnn] in question.  You can
          modify all the elements of an array by passing all the
          elements as scalars, but you have to use the * mechanism to
          push, pop or change the size of an array.  The * mechanism
          will probably be more efficient in any case.

          Since a *name value contains unprintable binary data, if it
          is used as an argument in a print, or as a %s argument in a
          printf or sprintf, it then has the value '*name', just so it
          prints out pretty.

          Even if you don't want to modify an array, this mechanism is
          useful for passing multiple arrays in a single LIST, since



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          normally the LIST mechanism will merge all the array values
          so that you can't extract out the individual arrays.

          RRRReeeegggguuuullllaaaarrrr EEEExxxxpppprrrreeeessssssssiiiioooonnnnssss

          The patterns used in pattern matching are regular
          expressions such as those supplied in the Version 8 regexp
          routines.  (In fact, the routines are derived from Henry
          Spencer's freely redistributable reimplementation of the V8
          routines.)  In addition, \w matches an alphanumeric
          character (including "_") and \W a nonalphanumeric.  Word
          boundaries may be matched by \b, and non-boundaries by \B.
          A whitespace character is matched by \s, non-whitespace by
          \S.  A numeric character is matched by \d, non-numeric by
          \D.  You may use \w, \s and \d within character classes.
          Also, \n, \r, \f, \t and \NNN have their normal
          interpretations.  Within character classes \b represents
          backspace rather than a word boundary.  Alternatives may be
          separated by |.  The bracketing construct ( ... ) may also
          be used, in which case \<digit> matches the digit'th
          substring.  (Outside of the pattern, always use $ instead of
          \ in front of the digit.  The scope of $<digit> (and $`, $&
          and $') extends to the end of the enclosing BLOCK or eval
          string, or to the next pattern match with subexpressions.
          The \<digit> notation sometimes works outside the current
          pattern, but should not be relied upon.)  You may have as
          many parentheses as you wish.  If you have more than 9
          substrings, the variables $10, $11, ... refer to the
          corresponding substring.  Within the pattern, \10, \11, etc.
          refer back to substrings if there have been at least that
          many left parens before the backreference.  Otherwise (for
          backward compatibilty) \10 is the same as \010, a backspace,
          and \11 the same as \011, a tab.  And so on.  (\1 through \9
          are always backreferences.)

          $+ returns whatever the last bracket match matched.  $&
          returns the entire matched string.  ($0 used to return the
          same thing, but not any more.)  $` returns everything before
          the matched string.  $' returns everything after the matched
          string.  Examples:

               s/^([^ ]*) *([^ ]*)/$2 $1/;   # swap first two words

               if (/Time: (..):(..):(..)/) {
                    $hours = $1;
                    $minutes = $2;
                    $seconds = $3;
               }

          By default, the ^ character is only guaranteed to match at
          the beginning of the string, the $ character only at the end
          (or before the newline at the end) and perl does certain



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          optimizations with the assumption that the string contains
          only one line.  The behavior of ^ and $ on embedded newlines
          will be inconsistent.  You may, however, wish to treat a
          string as a multi-line buffer, such that the ^ will match
          after any newline within the string, and $ will match before
          any newline.  At the cost of a little more overhead, you can
          do this by setting the variable $* to 1.  Setting it back to
          0 makes perl revert to its old behavior.

          To facilitate multi-line substitutions, the . character
          never matches a newline (even when $* is 0).  In particular,
          the following leaves a newline on the $_ string:

               $_ = <STDIN>;
               s/.*(some_string).*/$1/;

          If the newline is unwanted, try one of

               s/.*(some_string).*\n/$1/;
               s/.*(some_string)[^\000]*/$1/;
               s/.*(some_string)(.|\n)*/$1/;
               chop; s/.*(some_string).*/$1/;
               /(some_string)/ && ($_ = $1);

          Any item of a regular expression may be followed with digits
          in curly brackets of the form {n,m}, where n gives the
          minimum number of times to match the item and m gives the
          maximum.  The form {n} is equivalent to {n,n} and matches
          exactly n times.  The form {n,} matches n or more times.
          (If a curly bracket occurs in any other context, it is
          treated as a regular character.)  The * modifier is
          equivalent to {0,}, the + modifier to {1,} and the ?
          modifier to {0,1}.  There is no limit to the size of n or m,
          but large numbers will chew up more memory.

          You will note that all backslashed metacharacters in perl
          are alphanumeric, such as \b, \w, \n.  Unlike some other
          regular expression languages, there are no backslashed
          symbols that aren't alphanumeric.  So anything that looks
          like \\, \(, \), \<, \>, \{, or \} is always interpreted as
          a literal character, not a metacharacter.  This makes it
          simple to quote a string that you want to use for a pattern
          but that you are afraid might contain metacharacters.
          Simply quote all the non-alphanumeric characters:

               $pattern =~ s/(\W)/\\$1/g;


          FFFFoooorrrrmmmmaaaattttssss

          Output record formats for use with the write operator may
          declared as follows:



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              format NAME =
              FORMLIST
              .

          If name is omitted, format "STDOUT" is defined.  FORMLIST
          consists of a sequence of lines, each of which may be of one
          of three types:

          1.  A comment.

          2.  A "picture" line giving the format for one output line.

          3.  An argument line supplying values to plug into a picture
              line.

          Picture lines are printed exactly as they look, except for
          certain fields that substitute values into the line.  Each
          picture field starts with either @ or ^.  The @ field (not
          to be confused with the array marker @) is the normal case;
          ^ fields are used to do rudimentary multi-line text block
          filling.  The length of the field is supplied by padding out
          the field with multiple <, >, or | characters to specify,
          respectively, left justification, right justification, or
          centering.  As an alternate form of right justification, you
          may also use # characters (with an optional .) to specify a
          numeric field.  (Use of ^ instead of @ causes the field to
          be blanked if undefined.)  If any of the values supplied for
          these fields contains a newline, only the text up to the
          newline is printed.  The special field @* can be used for
          printing multi-line values.  It should appear by itself on a
          line.

          The values are specified on the following line, in the same
          order as the picture fields.  The values should be separated
          by commas.

          Picture fields that begin with ^ rather than @ are treated
          specially.  The value supplied must be a scalar variable
          name which contains a text string.  Perl puts as much text
          as it can into the field, and then chops off the front of
          the string so that the next time the variable is referenced,
          more of the text can be printed.  Normally you would use a
          sequence of fields in a vertical stack to print out a block
          of text.  If you like, you can end the final field with ...,
          which will appear in the output if the text was too long to
          appear in its entirety.  You can change which characters are
          legal to break on by changing the variable $: to a list of
          the desired characters.

          Since use of ^ fields can produce variable length records if
          the text to be formatted is short, you can suppress blank
          lines by putting the tilde (~) character anywhere in the



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          line.  (Normally you should put it in the front if possible,
          for visibility.)  The tilde will be translated to a space
          upon output.  If you put a second tilde contiguous to the
          first, the line will be repeated until all the fields on the
          line are exhausted.  (If you use a field of the @ variety,
          the expression you supply had better not give the same value
          every time forever!)

          Examples:

          # a report on the /etc/passwd file
          format STDOUT_TOP =
                                  Passwd File
          Name                Login    Office   Uid   Gid Home
          ------------------------------------------------------------------
          .
          format STDOUT =
          @<<<<<<<<<<<<<<<<<< @||||||| @<<<<<<@>>>> @>>>> @<<<<<<<<<<<<<<<<<
          $name,              $login,  $office,$uid,$gid, $home
          .

          # a report from a bug report form
          format STDOUT_TOP =
                                  Bug Reports
          @<<<<<<<<<<<<<<<<<<<<<<<     @|||         @>>>>>>>>>>>>>>>>>>>>>>>
          $system,                      $%,         $date
          ------------------------------------------------------------------
          .
          format STDOUT =
          Subject: @<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                   $subject
          Index: @<<<<<<<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                 $index,                       $description
          Priority: @<<<<<<<<<< Date: @<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                    $priority,        $date,   $description
          From: @<<<<<<<<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                $from,                         $description
          Assigned to: @<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                       $programmer,            $description
          ~                                    ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                                               $description
          ~                                    ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                                               $description
          ~                                    ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                                               $description
          ~                                    ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                                               $description
          ~                                    ^<<<<<<<<<<<<<<<<<<<<<<<...
                                               $description
          .

          It is possible to intermix prints with writes on the same



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          output channel, but you'll have to handle $- (lines left on
          the page) yourself.

          If you are printing lots of fields that are usually blank,
          you should consider using the reset operator between
          records.  Not only is it more efficient, but it can prevent
          the bug of adding another field and forgetting to zero it.

          IIIInnnntttteeeerrrrpppprrrroooocccceeeessssssss CCCCoooommmmmmmmuuuunnnniiiiccccaaaattttiiiioooonnnn

          The IPC facilities of perl are built on the Berkeley socket
          mechanism.  If you don't have sockets, you can ignore this
          section.  The calls have the same names as the corresponding
          system calls, but the arguments tend to differ, for two
          reasons.  First, perl file handles work differently than C
          file descriptors.  Second, perl already knows the length of
          its strings, so you don't need to pass that information.
          Here is a sample client (untested):

               ($them,$port) = @ARGV;
               $port = 2345 unless $port;
               $them = 'localhost' unless $them;

               $SIG{'INT'} = 'dokill';
               sub dokill { kill 9,$child if $child; }

               require 'sys/socket.ph';

               $sockaddr = 'S n a4 x8';
               chop($hostname = `hostname`);

               ($name, $aliases, $proto) = getprotobyname('tcp');
               ($name, $aliases, $port) = getservbyname($port, 'tcp')
                    unless $port =~ /^\d+$/;
               ($name, $aliases, $type, $len, $thisaddr) =
                                   gethostbyname($hostname);
               ($name, $aliases, $type, $len, $thataddr) = gethostbyname($them);

               $this = pack($sockaddr, &AF_INET, 0, $thisaddr);
               $that = pack($sockaddr, &AF_INET, $port, $thataddr);

               socket(S, &PF_INET, &SOCK_STREAM, $proto) || die "socket: $!";
               bind(S, $this) || die "bind: $!";
               connect(S, $that) || die "connect: $!";

               select(S); $| = 1; select(stdout);

               if ($child = fork) {
                    while (<>) {
                         print S;
                    }
                    sleep 3;



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                    do dokill();
               }
               else {
                    while (<S>) {
                         print;
                    }
               }

          And here's a server:

               ($port) = @ARGV;
               $port = 2345 unless $port;

               require 'sys/socket.ph';

               $sockaddr = 'S n a4 x8';

               ($name, $aliases, $proto) = getprotobyname('tcp');
               ($name, $aliases, $port) = getservbyname($port, 'tcp')
                    unless $port =~ /^\d+$/;

               $this = pack($sockaddr, &AF_INET, $port, "\0\0\0\0");

               select(NS); $| = 1; select(stdout);

               socket(S, &PF_INET, &SOCK_STREAM, $proto) || die "socket: $!";
               bind(S, $this) || die "bind: $!";
               listen(S, 5) || die "connect: $!";

               select(S); $| = 1; select(stdout);

               for (;;) {
                    print "Listening again\n";
                    ($addr = accept(NS,S)) || die $!;
                    print "accept ok\n";

                    ($af,$port,$inetaddr) = unpack($sockaddr,$addr);
                    @inetaddr = unpack('C4',$inetaddr);
                    print "$af $port @inetaddr\n";

                    while (<NS>) {
                         print;
                         print NS;
                    }
               }


          PPPPrrrreeeeddddeeeeffffiiiinnnneeeedddd NNNNaaaammmmeeeessss

          The following names have special meaning to perl.  I could
          have used alphabetic symbols for some of these, but I didn't
          want to take the chance that someone would say reset



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          "a-zA-Z" and wipe them all out.  You'll just have to suffer
          along with these silly symbols.  Most of them have
          reasonable mnemonics, or analogues in one of the shells.

          $_      The default input and pattern-searching space.  The
                  following pairs are equivalent:

                       while (<>) {...     # only equivalent in while!
                       while ($_ = <>) {...

                       /^Subject:/
                       $_ =~ /^Subject:/

                       y/a-z/A-Z/
                       $_ =~ y/a-z/A-Z/

                       chop
                       chop($_)

                  (Mnemonic: underline is understood in certain
                  operations.)

          $.      The current input line number of the last filehandle
                  that was read.  Readonly.  Remember that only an
                  explicit close on the filehandle resets the line
                  number.  Since <> never does an explicit close, line
                  numbers increase across ARGV files (but see examples
                  under eof).  (Mnemonic: many programs use . to mean
                  the current line number.)

          $/      The input record separator, newline by default.
                  Works like awk's RS variable, including treating
                  blank lines as delimiters if set to the null string.
                  You may set it to a multicharacter string to match a
                  multi-character delimiter.  Note that setting it to
                  "\n\n" means something slightly different than
                  setting it to "", if the file contains consecutive
                  blank lines.  Setting it to "" will treat two or
                  more consecutive blank lines as a single blank line.
                  Setting it to "\n\n" will blindly assume that the
                  next input character belongs to the next paragraph,
                  even if it's a newline.  (Mnemonic: / is used to
                  delimit line boundaries when quoting poetry.)

          $,      The output field separator for the print operator.
                  Ordinarily the print operator simply prints out the
                  comma separated fields you specify.  In order to get
                  behavior more like awk, set this variable as you
                  would set awk's OFS variable to specify what is
                  printed between fields.  (Mnemonic: what is printed
                  when there is a , in your print statement.)




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          $"      This is like $, except that it applies to array
                  values interpolated into a double-quoted string (or
                  similar interpreted string).  Default is a space.
                  (Mnemonic: obvious, I think.)

          $\      The output record separator for the print operator.
                  Ordinarily the print operator simply prints out the
                  comma separated fields you specify, with no trailing
                  newline or record separator assumed.  In order to
                  get behavior more like awk, set this variable as you
                  would set awk's ORS variable to specify what is
                  printed at the end of the print.  (Mnemonic: you set
                  $\ instead of adding \n at the end of the print.
                  Also, it's just like /, but it's what you get "back"
                  from perl.)

          $#      The output format for printed numbers.  This
                  variable is a half-hearted attempt to emulate awk's
                  OFMT variable.  There are times, however, when awk
                  and perl have differing notions of what is in fact
                  numeric.  Also, the initial value is %.20g rather
                  than %.6g, so you need to set $# explicitly to get
                  awk's value.  (Mnemonic: # is the number sign.)

          $%      The current page number of the currently selected
                  output channel.  (Mnemonic: % is page number in
                  nroff.)

          $=      The current page length (printable lines) of the
                  currently selected output channel.  Default is 60.
                  (Mnemonic: = has horizontal lines.)

          $-      The number of lines left on the page of the
                  currently selected output channel.  (Mnemonic:
                  lines_on_page - lines_printed.)

          $~      The name of the current report format for the
                  currently selected output channel.  Default is name
                  of the filehandle.  (Mnemonic: brother to $^.)

          $^      The name of the current top-of-page format for the
                  currently selected output channel.  Default is name
                  of the filehandle with "_TOP" appended.  (Mnemonic:
                  points to top of page.)

          $|      If set to nonzero, forces a flush after every write
                  or print on the currently selected output channel.
                  Default is 0.  Note that STDOUT will typically be
                  line buffered if output is to the terminal and block
                  buffered otherwise.  Setting this variable is useful
                  primarily when you are outputting to a pipe, such as
                  when you are running a perl script under rsh and



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                  want to see the output as it's happening.
                  (Mnemonic: when you want your pipes to be piping
                  hot.)

          $$      The process number of the perl running this script.
                  (Mnemonic: same as shells.)

          $?      The status returned by the last pipe close, backtick
                  (``) command or system operator.  Note that this is
                  the status word returned by the wait() system call,
                  so the exit value of the subprocess is actually ($?
                  >> 8).  $? & 255 gives which signal, if any, the
                  process died from, and whether there was a core
                  dump.  (Mnemonic: similar to sh and ksh.)

          $&      The string matched by the last successful pattern
                  match (not counting any matches hidden within a
                  BLOCK or eval enclosed by the current BLOCK).
                  (Mnemonic: like & in some editors.)

          $`      The string preceding whatever was matched by the
                  last successful pattern match (not counting any
                  matches hidden within a BLOCK or eval enclosed by
                  the current BLOCK).  (Mnemonic: ` often precedes a
                  quoted string.)

          $'      The string following whatever was matched by the
                  last successful pattern match (not counting any
                  matches hidden within a BLOCK or eval enclosed by
                  the current BLOCK).  (Mnemonic: ' often follows a
                  quoted string.)  Example:

                       $_ = 'abcdefghi';
                       /def/;
                       print "$`:$&:$'\n";      # prints abc:def:ghi


          $+      The last bracket matched by the last search pattern.
                  This is useful if you don't know which of a set of
                  alternative patterns matched.  For example:

                      /Version: (.*)|Revision: (.*)/ && ($rev = $+);

                  (Mnemonic: be positive and forward looking.)

          $*      Set to 1 to do multiline matching within a string, 0
                  to tell perl that it can assume that strings contain
                  a single line, for the purpose of optimizing pattern
                  matches.  Pattern matches on strings containing
                  multiple newlines can produce confusing results when
                  $* is 0.  Default is 0.  (Mnemonic: * matches
                  multiple things.)  Note that this variable only



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                  influences the interpretation of ^ and $.  A literal
                  newline can be searched for even when $* == 0.

          $0      Contains the name of the file containing the perl
                  script being executed.  Assigning to $0 modifies the
                  argument area that the ps(1) program sees.
                  (Mnemonic: same as sh and ksh.)

          $<digit>
                  Contains the subpattern from the corresponding set
                  of parentheses in the last pattern matched, not
                  counting patterns matched in nested blocks that have
                  been exited already.  (Mnemonic: like \digit.)

          $[      The index of the first element in an array, and of
                  the first character in a substring.  Default is 0,
                  but you could set it to 1 to make perl behave more
                  like awk (or Fortran) when subscripting and when
                  evaluating the index() and substr() functions.
                  (Mnemonic: [ begins subscripts.)

          $]      The string printed out when you say "perl -v".  It
                  can be used to determine at the beginning of a
                  script whether the perl interpreter executing the
                  script is in the right range of versions.  If used
                  in a numeric context, returns the version +
                  patchlevel / 1000.  Example:

                       # see if getc is available
                          ($version,$patchlevel) =
                             $] =~ /(\d+\.\d+).*\nPatch level: (\d+)/;
                          print STDERR "(No filename completion available.)\n"
                             if $version * 1000 + $patchlevel < 2016;

                  or, used numerically,

                       warn "No checksumming!\n" if $] < 3.019;

                  (Mnemonic: Is this version of perl in the right
                  bracket?)

          $;      The subscript separator for multi-dimensional array
                  emulation.  If you refer to an associative array
                  element as
                       $foo{$a,$b,$c}

                  it really means

                       $foo{join($;, $a, $b, $c)}

                  But don't put




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                       @foo{$a,$b,$c}      # a slice--note the @

                  which means

                       ($foo{$a},$foo{$b},$foo{$c})

                  Default is "\034", the same as SUBSEP in awk.  Note
                  that if your keys contain binary data there might
                  not be any safe value for $;.  (Mnemonic: comma (the
                  syntactic subscript separator) is a semi-semicolon.
                  Yeah, I know, it's pretty lame, but $, is already
                  taken for something more important.)

          $!      If used in a numeric context, yields the current
                  value of errno, with all the usual caveats.  (This
                  means that you shouldn't depend on the value of $!
                  to be anything in particular unless you've gotten a
                  specific error return indicating a system error.)
                  If used in a string context, yields the
                  corresponding system error string.  You can assign
                  to $! in order to set errno if, for instance, you
                  want $! to return the string for error n, or you
                  want to set the exit value for the die operator.
                  (Mnemonic: What just went bang?)

          $@      The perl syntax error message from the last eval
                  command.  If null, the last eval parsed and executed
                  correctly (although the operations you invoked may
                  have failed in the normal fashion).  (Mnemonic:
                  Where was the syntax error "at"?)

          $<      The real uid of this process.  (Mnemonic: it's the
                  uid you came FROM, if you're running setuid.)

          $>      The effective uid of this process.  Example:

                       $< = $>;  # set real uid to the effective uid
                       ($<,$>) = ($>,$<);  # swap real and effective uid

                  (Mnemonic: it's the uid you went TO, if you're
                  running setuid.)  Note: $< and $> can only be
                  swapped on machines supporting setreuid().

          $(      The real gid of this process.  If you are on a
                  machine that supports membership in multiple groups
                  simultaneously, gives a space separated list of
                  groups you are in.  The first number is the one
                  returned by getgid(), and the subsequent ones by
                  getgroups(), one of which may be the same as the
                  first number.  (Mnemonic: parentheses are used to
                  GROUP things.  The real gid is the group you LEFT,
                  if you're running setgid.)



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          $)      The effective gid of this process.  If you are on a
                  machine that supports membership in multiple groups
                  simultaneously, gives a space separated list of
                  groups you are in.  The first number is the one
                  returned by getegid(), and the subsequent ones by
                  getgroups(), one of which may be the same as the
                  first number.  (Mnemonic: parentheses are used to
                  GROUP things.  The effective gid is the group that's
                  RIGHT for you, if you're running setgid.)

                  Note: $<, $>, $( and $) can only be set on machines
                  that support the corresponding set[re][ug]id()
                  routine.  $( and $) can only be swapped on machines
                  supporting setregid().

          $:      The current set of characters after which a string
                  may be broken to fill continuation fields (starting
                  with ^) in a format.  Default is " \n-", to break on
                  whitespace or hyphens.  (Mnemonic: a "colon" in
                  poetry is a part of a line.)

          $^D     The current value of the debugging flags.
                  (Mnemonic: value of ----DDDD switch.)

          $^F     The maximum system file descriptor, ordinarily 2.
                  System file descriptors are passed to subprocesses,
                  while higher file descriptors are not.  During an
                  open, system file descriptors are preserved even if
                  the open fails.  Ordinary file descriptors are
                  closed before the open is attempted.

          $^I     The current value of the inplace-edit extension.
                  Use undef to disable inplace editing.  (Mnemonic:
                  value of ----iiii switch.)

          $^L     What formats output to perform a formfeed.  Default
                  is \f.

          $^P     The internal flag that the debugger clears so that
                  it doesn't debug itself.  You could conceivable
                  disable debugging yourself by clearing it.

          $^T     The time at which the script began running, in
                  seconds since the epoch.  The values returned by the
                  ----MMMM ,,,, ----AAAA and ----CCCC filetests are based on this value.

          $^W     The current value of the warning switch.  (Mnemonic:
                  related to the ----wwww switch.)

          $^X     The name that Perl itself was executed as, from
                  argv[0].




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          $ARGV   contains the name of the current file when reading
                  from <>.

          @ARGV   The array ARGV contains the command line arguments
                  intended for the script.  Note that $#ARGV is the
                  generally number of arguments minus one, since
                  $ARGV[0] is the first argument, NOT the command
                  name.  See $0 for the command name.

          @INC    The array INC contains the list of places to look
                  for perl scripts to be evaluated by the "do EXPR"
                  command or the "require" command.  It initially
                  consists of the arguments to any ----IIII command line
                  switches, followed by the default perl library,
                  probably "/usr/local/lib/perl", followed by ".", to
                  represent the current directory.

          %INC    The associative array INC contains entries for each
                  filename that has been included via "do" or
                  "require".  The key is the filename you specified,
                  and the value is the location of the file actually
                  found.  The "require" command uses this array to
                  determine whether a given file has already been
                  included.

          $ENV{expr}
                  The associative array ENV contains your current
                  environment.  Setting a value in ENV changes the
                  environment for child processes.

          $SIG{expr}
                  The associative array SIG is used to set signal
                  handlers for various signals.  Example:

                       sub handler {  # 1st argument is signal name
                            local($sig) = @_;
                            print "Caught a SIG$sig--shutting down\n";
                            close(LOG);
                            exit(0);
                       }

                       $SIG{'INT'} = 'handler';
                       $SIG{'QUIT'} = 'handler';
                       ...
                       $SIG{'INT'} = 'DEFAULT'; # restore default action
                       $SIG{'QUIT'} = 'IGNORE'; # ignore SIGQUIT

                  The SIG array only contains values for the signals
                  actually set within the perl script.






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          PPPPaaaacccckkkkaaaaggggeeeessss

          Perl provides a mechanism for alternate namespaces to
          protect packages from stomping on each others variables.  By
          default, a perl script starts compiling into the package
          known as "main".  By use of the package declaration, you can
          switch namespaces.  The scope of the package declaration is
          from the declaration itself to the end of the enclosing
          block (the same scope as the local() operator).  Typically
          it would be the first declaration in a file to be included
          by the "require" operator.  You can switch into a package in
          more than one place; it merely influences which symbol table
          is used by the compiler for the rest of that block.  You can
          refer to variables and filehandles in other packages by
          prefixing the identifier with the package name and a single
          quote.  If the package name is null, the "main" package as
          assumed.

          Only identifiers starting with letters are stored in the
          packages symbol table.  All other symbols are kept in
          package "main".  In addition, the identifiers STDIN, STDOUT,
          STDERR, ARGV, ARGVOUT, ENV, INC and SIG are forced to be in
          package "main", even when used for other purposes than their
          built-in one.  Note also that, if you have a package called
          "m", "s" or "y", the you can't use the qualified form of an
          identifier since it will be interpreted instead as a pattern
          match, a substitution or a translation.

          Eval'ed strings are compiled in the package in which the
          eval was compiled in.  (Assignments to $SIG{}, however,
          assume the signal handler specified is in the main package.
          Qualify the signal handler name if you wish to have a signal
          handler in a package.)  For an example, examine perldb.pl in
          the perl library.  It initially switches to the DB package
          so that the debugger doesn't interfere with variables in the
          script you are trying to debug.  At various points, however,
          it temporarily switches back to the main package to evaluate
          various expressions in the context of the main package.

          The symbol table for a package happens to be stored in the
          associative array of that name prepended with an underscore.
          The value in each entry of the associative array is what you
          are referring to when you use the *name notation.  In fact,
          the following have the same effect (in package main,
          anyway), though the first is more efficient because it does
          the symbol table lookups at compile time:

               local(*foo) = *bar;
               local($_main{'foo'}) = $_main{'bar'};

          You can use this to print out all the variables in a
          package, for instance.  Here is dumpvar.pl from the perl



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          library:
               package dumpvar;

               sub main'dumpvar {
                   ($package) = @_;
                   local(*stab) = eval("*_$package");
                   while (($key,$val) = each(%stab)) {
                       {
                           local(*entry) = $val;
                           if (defined $entry) {
                               print "\$$key = '$entry'\n";
                           }
                           if (defined @entry) {
                               print "\@$key = (\n";
                               foreach $num ($[ .. $#entry) {
                                   print "  $num\t'",$entry[$num],"'\n";
                               }
                               print ")\n";
                           }
                           if ($key ne "_$package" && defined %entry) {
                               print "\%$key = (\n";
                               foreach $key (sort keys(%entry)) {
                                   print "  $key\t'",$entry{$key},"'\n";
                               }
                               print ")\n";
                           }
                       }
                   }
               }

          Note that, even though the subroutine is compiled in package
          dumpvar, the name of the subroutine is qualified so that its
          name is inserted into package "main".

          SSSSttttyyyylllleeee

          Each programmer will, of course, have his or her own
          preferences in regards to formatting, but there are some
          general guidelines that will make your programs easier to
          read.

          1.  Just because you CAN do something a particular way
              doesn't mean that you SHOULD do it that way.  Perl is
              designed to give you several ways to do anything, so
              consider picking the most readable one.  For instance

                   open(FOO,$foo) || die "Can't open $foo: $!";

              is better than

                   die "Can't open $foo: $!" unless open(FOO,$foo);




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              because the second way hides the main point of the
              statement in a modifier.  On the other hand

                   print "Starting analysis\n" if $verbose;

              is better than

                   $verbose && print "Starting analysis\n";

              since the main point isn't whether the user typed -v or
              not.

              Similarly, just because an operator lets you assume
              default arguments doesn't mean that you have to make use
              of the defaults.  The defaults are there for lazy
              systems programmers writing one-shot programs.  If you
              want your program to be readable, consider supplying the
              argument.

              Along the same lines, just because you can omit
              parentheses in many places doesn't mean that you ought
              to:

                   return print reverse sort num values array;
                   return print(reverse(sort num (values(%array))));

              When in doubt, parenthesize.  At the very least it will
              let some poor schmuck bounce on the % key in vi.

              Even if you aren't in doubt, consider the mental welfare
              of the person who has to maintain the code after you,
              and who will probably put parens in the wrong place.

          2.  Don't go through silly contortions to exit a loop at the
              top or the bottom, when perl provides the "last"
              operator so you can exit in the middle.  Just outdent it
              a little to make it more visible:

                  line:
                   for (;;) {
                       statements;
                   last line if $foo;
                       next line if /^#/;
                       statements;
                   }


          3.  Don't be afraid to use loop labels--they're there to
              enhance readability as well as to allow multi-level loop
              breaks.  See last example.





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          4.  For portability, when using features that may not be
              implemented on every machine, test the construct in an
              eval to see if it fails.  If you know what version or
              patchlevel a particular feature was implemented, you can
              test $] to see if it will be there.

          5.  Choose mnemonic identifiers.

          6.  Be consistent.

          DDDDeeeebbbbuuuuggggggggiiiinnnngggg

          If you invoke perl with a ----dddd switch, your script will be run
          under a debugging monitor.  It will halt before the first
          executable statement and ask you for a command, such as:

          h           Prints out a help message.

          T           Stack trace.

          s           Single step.  Executes until it reaches the
                      beginning of another statement.

          n           Next.  Executes over subroutine calls, until it
                      reaches the beginning of the next statement.

          f           Finish.  Executes statements until it has
                      finished the current subroutine.

          c           Continue.  Executes until the next breakpoint is
                      reached.

          c line      Continue to the specified line.  Inserts a one-
                      time-only breakpoint at the specified line.

          <CR>        Repeat last n or s.

          l min+incr  List incr+1 lines starting at min.  If min is
                      omitted, starts where last listing left off.  If
                      incr is omitted, previous value of incr is used.

          l min-max   List lines in the indicated range.

          l line      List just the indicated line.

          l           List next window.

          -           List previous window.

          w line      List window around line.





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          l subname   List subroutine.  If it's a long subroutine it
                      just lists the beginning.  Use "l" to list more.

          /pattern/   Regular expression search forward for pattern;
                      the final / is optional.

          ?pattern?   Regular expression search backward for pattern;
                      the final ? is optional.

          L           List lines that have breakpoints or actions.

          S           Lists the names of all subroutines.

          t           Toggle trace mode on or off.

          b line condition
                      Set a breakpoint.  If line is omitted, sets a
                      breakpoint on the line that is about to be
                      executed.  If a condition is specified, it is
                      evaluated each time the statement is reached and
                      a breakpoint is taken only if the condition is
                      true.  Breakpoints may only be set on lines that
                      begin an executable statement.

          b subname condition
                      Set breakpoint at first executable line of
                      subroutine.

          d line      Delete breakpoint.  If line is omitted, deletes
                      the breakpoint on the line that is about to be
                      executed.

          D           Delete all breakpoints.

          a line command
                      Set an action for line.  A multi-line command
                      may be entered by backslashing the newlines.

          A           Delete all line actions.

          < command   Set an action to happen before every debugger
                      prompt.  A multi-line command may be entered by
                      backslashing the newlines.

          > command   Set an action to happen after the prompt when
                      you've just given a command to return to
                      executing the script.  A multi-line command may
                      be entered by backslashing the newlines.

          V package   List all variables in package.  Default is main
                      package.




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          ! number    Redo a debugging command.  If number is omitted,
                      redoes the previous command.

          ! -number   Redo the command that was that many commands
                      ago.

          H -number   Display last n commands.  Only commands longer
                      than one character are listed.  If number is
                      omitted, lists them all.

          q or ^D     Quit.

          command     Execute command as a perl statement.  A missing
                      semicolon will be supplied.

          p expr      Same as "print DB'OUT expr".  The DB'OUT
                      filehandle is opened to /dev/tty, regardless of
                      where STDOUT may be redirected to.

          If you want to modify the debugger, copy perldb.pl from the
          perl library to your current directory and modify it as
          necessary.  (You'll also have to put -I. on your command
          line.)  You can do some customization by setting up a
          .perldb file which contains initialization code.  For
          instance, you could make aliases like these:

              $DB'alias{'len'} = 's/^len(.*)/p length($1)/';
              $DB'alias{'stop'} = 's/^stop (at|in)/b/';
              $DB'alias{'.'} =
                's/^\./p "\$DB\'sub(\$DB\'line):\t",\$DB\'line[\$DB\'line]/';


          SSSSeeeettttuuuuiiiidddd SSSSccccrrrriiiippppttttssss

          Perl is designed to make it easy to write secure setuid and
          setgid scripts.  Unlike shells, which are based on multiple
          substitution passes on each line of the script, perl uses a
          more conventional evaluation scheme with fewer hidden
          "gotchas".  Additionally, since the language has more
          built-in functionality, it has to rely less upon external
          (and possibly untrustworthy) programs to accomplish its
          purposes.

          In an unpatched 4.2 or 4.3bsd kernel, setuid scripts are
          intrinsically insecure, but this kernel feature can be
          disabled.  If it is, perl can emulate the setuid and setgid
          mechanism when it notices the otherwise useless setuid/gid
          bits on perl scripts.  If the kernel feature isn't disabled,
          perl will complain loudly that your setuid script is
          insecure.  You'll need to either disable the kernel setuid
          script feature, or put a C wrapper around the script.




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          When perl is executing a setuid script, it takes special
          precautions to prevent you from falling into any obvious
          traps.  (In some ways, a perl script is more secure than the
          corresponding C program.)  Any command line argument,
          environment variable, or input is marked as "tainted", and
          may not be used, directly or indirectly, in any command that
          invokes a subshell, or in any command that modifies files,
          directories or processes.  Any variable that is set within
          an expression that has previously referenced a tainted value
          also becomes tainted (even if it is logically impossible for
          the tainted value to influence the variable).  For example:

               $foo = shift;            # $foo is tainted
               $bar = $foo,'bar';       # $bar is also tainted
               $xxx = <>;               # Tainted
               $path = $ENV{'PATH'};    # Tainted, but see below
               $abc = 'abc';            # Not tainted

               system "echo $foo";      # Insecure
               system "/bin/echo", $foo;     # Secure (doesn't use sh)
               system "echo $bar";      # Insecure
               system "echo $abc";      # Insecure until PATH set

               $ENV{'PATH'} = '/bin:/usr/bin';
               $ENV{'IFS'} = '' if $ENV{'IFS'} ne '';

               $path = $ENV{'PATH'};    # Not tainted
               system "echo $abc";      # Is secure now!

               open(FOO,"$foo");        # OK
               open(FOO,">$foo");       # Not OK

               open(FOO,"echo $foo|");  # Not OK, but...
               open(FOO,"-|") || exec 'echo', $foo;    # OK

               $zzz = `echo $foo`;      # Insecure, zzz tainted

               unlink $abc,$foo;        # Insecure
               umask $foo;              # Insecure

               exec "echo $foo";        # Insecure
               exec "echo", $foo;       # Secure (doesn't use sh)
               exec "sh", '-c', $foo;   # Considered secure, alas

          The taintedness is associated with each scalar value, so
          some elements of an array can be tainted, and others not.

          If you try to do something insecure, you will get a fatal
          error saying something like "Insecure dependency" or
          "Insecure PATH".  Note that you can still write an insecure
          system call or exec, but only by explicitly doing something
          like the last example above.  You can also bypass the



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          tainting mechanism by referencing subpatterns--perl presumes
          that if you reference a substring using $1, $2, etc, you
          knew what you were doing when you wrote the pattern:

               $ARGV[0] =~ /^-P(\w+)$/;
               $printer = $1;      # Not tainted

          This is fairly secure since \w+ doesn't match shell
          metacharacters.  Use of .+ would have been insecure, but
          perl doesn't check for that, so you must be careful with
          your patterns.  This is the ONLY mechanism for untainting
          user supplied filenames if you want to do file operations on
          them (unless you make $> equal to $<).

          It's also possible to get into trouble with other operations
          that don't care whether they use tainted values.  Make
          judicious use of the file tests in dealing with any user-
          supplied filenames.  When possible, do opens and such after
          setting $> = $<.  Perl doesn't prevent you from opening
          tainted filenames for reading, so be careful what you print
          out.  The tainting mechanism is intended to prevent stupid
          mistakes, not to remove the need for thought.

     EEEENNNNVVVVIIIIRRRROOOONNNNMMMMEEEENNNNTTTT
          HOME        Used if chdir has no argument.

          LOGDIR      Used if chdir has no argument and HOME is not
                      set.

          PATH        Used in executing subprocesses, and in finding
                      the script if -S is used.

          PERLLIB     A colon-separated list of directories in which
                      to look for Perl library files before looking in
                      the standard library and the current directory.

          PERLDB      The command used to get the debugger code.  If
                      unset, uses

                           require 'perldb.pl'


          Apart from these, perl uses no other environment variables,
          except to make them available to the script being executed,
          and to child processes.  However, scripts running setuid
          would do well to execute the following lines before doing
          anything else, just to keep people honest:

              $ENV{'PATH'} = '/bin:/usr/bin';    # or whatever you need
              $ENV{'SHELL'} = '/bin/sh' if $ENV{'SHELL'} ne '';
              $ENV{'IFS'} = '' if $ENV{'IFS'} ne '';




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     AAAAUUUUTTTTHHHHOOOORRRR
          Larry Wall <[e-mail]>
          MS-DOS port by Diomidis Spinellis <[e-mail]>

     FFFFIIIILLLLEEEESSSS
          /tmp/perl-eXXXXXX   temporary file for ----eeee commands.

     SSSSEEEEEEEE AAAALLLLSSSSOOOO
          a2p  awk to perl translator
          s2p  sed to perl translator

     DDDDIIIIAAAAGGGGNNNNOOOOSSSSTTTTIIIICCCCSSSS
          Compilation errors will tell you the line number of the
          error, with an indication of the next token or token type
          that was to be examined.  (In the case of a script passed to
          perl via ----eeee switches, each ----eeee is counted as one line.)

          Setuid scripts have additional constraints that can produce
          error messages such as "Insecure dependency".  See the
          section on setuid scripts.

     TTTTRRRRAAAAPPPPSSSS
          Accustomed awk users should take special note of the
          following:

          *   Semicolons are required after all simple statements in
              perl (except at the end of a block).  Newline is not a
              statement delimiter.

          *   Curly brackets are required on ifs and whiles.

          *   Variables begin with $ or @ in perl.

          *   Arrays index from 0 unless you set $[.  Likewise string
              positions in substr() and index().

          *   You have to decide whether your array has numeric or
              string indices.

          *   Associative array values do not spring into existence
              upon mere reference.

          *   You have to decide whether you want to use string or
              numeric comparisons.

          *   Reading an input line does not split it for you.  You
              get to split it yourself to an array.  And the split
              operator has different arguments.

          *   The current input line is normally in $_, not $0.  It
              generally does not have the newline stripped.  ($0 is
              the name of the program executed.)



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          *   $<digit> does not refer to fields--it refers to
              substrings matched by the last match pattern.

          *   The print statement does not add field and record
              separators unless you set $, and $\.

          *   You must open your files before you print to them.

          *   The range operator is "..", not comma.  (The comma
              operator works as in C.)

          *   The match operator is "=~", not "~".  ("~" is the one's
              complement operator, as in C.)

          *   The exponentiation operator is "**", not "^".  ("^" is
              the XOR operator, as in C.)

          *   The concatenation operator is ".", not the null string.
              (Using the null string would render "/pat/ /pat/"
              unparsable, since the third slash would be interpreted
              as a division operator--the tokener is in fact slightly
              context sensitive for operators like /, ?, and <.  And
              in fact, . itself can be the beginning of a number.)

          *   Next, exit and continue work differently.

          *   The following variables work differently

                     Awk               Perl
                     ARGC              $#ARGV
                     ARGV[0]           $0
                     FILENAME          $ARGV
                     FNR               $. - something
                     FS                (whatever you like)
                     NF                $#Fld, or some such
                     NR                $.
                     OFMT              $#
                     OFS               $,
                     ORS               $\
                     RLENGTH           length($&)
                     RS                $/
                     RSTART            length($`)
                     SUBSEP            $;


          *   When in doubt, run the awk construct through a2p and see
              what it gives you.

          Cerebral C programmers should take note of the following:

          *   Curly brackets are required on ifs and whiles.




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          *   You should use "elsif" rather than "else if"

          *   Break and continue become last and next, respectively.

          *   There's no switch statement.

          *   Variables begin with $ or @ in perl.

          *   Printf does not implement *.

          *   Comments begin with #, not /*.

          *   You can't take the address of anything.

          *   ARGV must be capitalized.

          *   The "system" calls link, unlink, rename, etc. return
              nonzero for success, not 0.

          *   Signal handlers deal with signal names, not numbers.

          Seasoned sed programmers should take note of the following:

          *   Backreferences in substitutions use $ rather than \.

          *   The pattern matching metacharacters (, ), and | do not
              have backslashes in front.

          *   The range operator is .. rather than comma.

          Sharp shell programmers should take note of the following:

          *   The backtick operator does variable interpretation
              without regard to the presence of single quotes in the
              command.

          *   The backtick operator does no translation of the return
              value, unlike csh.

          *   Shells (especially csh) do several levels of
              substitution on each command line.  Perl does
              substitution only in certain constructs such as double
              quotes, backticks, angle brackets and search patterns.

          *   Shells interpret scripts a little bit at a time.  Perl
              compiles the whole program before executing it.

          *   The arguments are available via @ARGV, not $1, $2, etc.

          *   The environment is not automatically made available as
              variables.




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     EEEERRRRRRRRAAAATTTTAAAA AAAANNNNDDDD AAAADDDDDDDDEEEENNNNDDDDAAAA
          The Perl book, Programming Perl , has the following
          omissions and goofs.

          On page 5, the examples which read

               eval "/usr/bin/perl

          should read

               eval "exec /usr/bin/perl


          On page 195, the equivalent to the System V sum program only
          works for very small files.  To do larger files, use

               undef $/;
               $checksum = unpack("%32C*",<>) % 32767;


          The descriptions of alarm and sleep refer to signal
          SIGALARM.  These should refer to SIGALRM.

          The ----0000 switch to set the initial value of $/ was added to
          Perl after the book went to press.

          The ----llll switch now does automatic line ending processing.

          The qx// construct is now a synonym for backticks.

          $0 may now be assigned to set the argument displayed by ps
          (1).

          The new @###.## format was omitted accidentally from the
          description on formats.

          It wasn't known at press time that s///ee caused multiple
          evaluations of the replacement expression.  This is to be
          construed as a feature.

          (LIST) x $count now does array replication.

          There is now no limit on the number of parentheses in a
          regular expression.

          In double-quote context, more escapes are supported: \e, \a,
          \x1b, \c[, \l, \L, \u, \U, \E.  The latter five control
          up/lower case translation.

          The $$$$//// variable may now be set to a multi-character
          delimiter.




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          There is now a g modifier on ordinary pattern matching that
          causes it to iterate through a string finding multiple
          matches.

          All of the $^X variables are new except for $^T.

          The default top-of-form format for FILEHANDLE is now
          FILEHANDLE_TOP rather than top.

          The eval {} and sort {} constructs were added in version
          4.018.

          The v and V (little-endian) template options for pack and
          unpack were added in 4.019.

     BBBBUUUUGGGGSSSS
          Perl is at the mercy of your machine's definitions of
          various operations such as type casting, atof() and
          sprintf().

          If your stdio requires an seek or eof between reads and
          writes on a particular stream, so does perl.  (This doesn't
          apply to sysread() and syswrite().)

          While none of the built-in data types have any arbitrary
          size limits (apart from memory size), there are still a few
          arbitrary limits: a given identifier may not be longer than
          255 characters, and no component of your PATH may be longer
          than 255 if you use -S.  A regular expression may not
          compile to more than 32767 bytes internally.

          Perl actually stands for Pathologically Eclectic Rubbish
          Lister, but don't tell anyone I said that.






















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