Usenet 1994 October/usenetsourcesnewsgroupsinfomagicoctober1994disk2.iso/misc/volume18/perl/part02

Internet Message Format | 1991-04-14 | 50.4 KB

From: [e-mail] (Larry Wall)
Newsgroups: comp.sources.misc
Subject: v18i020:  perl - The perl programming language, Part02/36
Message-ID: <[e-mail]>
Date: 15 Apr 91 01:52:34 GMT
Approved: [e-mail]
X-Checksum-Snefru: 3c60c4e2 36f7a6c1 6200cf17 b78f69c1

Submitted-by: Larry Wall <[e-mail]>
Posting-number: Volume 18, Issue 20
Archive-name: perl/part02

[There are 36 kits for perl version 4.0.]

#! /bin/sh

# Make a new directory for the perl sources, cd to it, and run kits 1
# thru 36 through sh.  When all 36 kits have been run, read README.

echo "This is perl 4.0 kit 2 (of 36).  If kit 2 is complete, the line"
echo '"'"End of kit 2 (of 36)"'" will echo at the end.'
echo ""
export PATH || (echo "You didn't use sh, you clunch." ; kill $$)
mkdir  2>/dev/null
echo Extracting perl.man:AA
sed >perl.man:AA <<'!STUFFY!FUNK!' -e 's/X//'
X.rn '' }`
X''' $RCSfile: perl.man,v $$Revision: 4.0.1.1 $$Date: 91/04/11 17:50:44 $
X'''
X''' $Log:    perl.man,v $
X''' Revision 4.0.1.1  91/04/11  17:50:44  lwall
X''' patch1: fixed some typos
X'''
X''' Revision 4.0  91/03/20  01:38:08  lwall
X''' 4.0 baseline.
X'''
X'''
X.de Sh
X.br
X.ne 5
X.PP
X\fB\\$1\fR
X.PP
X..
X.de Sp
X.if t .sp .5v
X.if n .sp
X..
X.de Ip
X.br
X.ie \\n(.$>=3 .ne \\$3
X.el .ne 3
X.IP "\\$1" \\$2
X..
X'''
X'''     Set up \*(-- to give an unbreakable dash;
X'''     string Tr holds user defined translation string.
X'''     Bell System Logo is used as a dummy character.
X'''
X.tr \(*W-|\(bv\*(Tr
X.ie n \{\
X.ds -- \(*W-
X.if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
X.if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch
X.ds L" ""
X.ds R" ""
X.ds L' '
X.ds R' '
X'br\}
X.el\{\
X.ds -- \(em\|
X.tr \*(Tr
X.ds L" ``
X.ds R" ''
X.ds L' `
X.ds R' '
X'br\}
X.TH PERL 1 "\*(RP"
X.UC
X.SH NAME
Xperl \- Practical Extraction and Report Language
X.SH SYNOPSIS
X.B perl
X[options] filename args
X.SH DESCRIPTION
X.I Perl
Xis an interpreted language optimized for scanning arbitrary text files,
Xextracting information from those text files, and printing reports based
Xon that information.
XIt's also a good language for many system management tasks.
XThe language is intended to be practical (easy to use, efficient, complete)
Xrather than beautiful (tiny, elegant, minimal).
XIt combines (in the author's opinion, anyway) some of the best features of C,
X\fIsed\fR, \fIawk\fR, and \fIsh\fR,
Xso people familiar with those languages should have little difficulty with it.
X(Language historians will also note some vestiges of \fIcsh\fR, Pascal, and
Xeven BASIC-PLUS.)
XExpression syntax corresponds quite closely to C expression syntax.
XUnlike most Unix utilities,
X.I perl
Xdoes not arbitrarily limit the size of your data\*(--if you've got
Xthe memory,
X.I perl
Xcan slurp in your whole file as a single string.
XRecursion is of unlimited depth.
XAnd the hash tables used by associative arrays grow as necessary to prevent
Xdegraded performance.
X.I Perl
Xuses sophisticated pattern matching techniques to scan large amounts of
Xdata very quickly.
XAlthough optimized for scanning text,
X.I perl
Xcan also deal with binary data, and can make dbm files look like associative
Xarrays (where dbm is available).
XSetuid
X.I perl
Xscripts are safer than C programs
Xthrough a dataflow tracing mechanism which prevents many stupid security holes.
XIf you have a problem that would ordinarily use \fIsed\fR
Xor \fIawk\fR or \fIsh\fR, but it
Xexceeds their capabilities or must run a little faster,
Xand you don't want to write the silly thing in C, then
X.I perl
Xmay be for you.
XThere are also translators to turn your
X.I sed
Xand
X.I awk
Xscripts into
X.I perl
Xscripts.
XOK, enough hype.
X.PP
XUpon startup,
X.I perl
Xlooks for your script in one of the following places:
X.Ip 1. 4 2
XSpecified line by line via
X.B \-e
Xswitches on the command line.
X.Ip 2. 4 2
XContained in the file specified by the first filename on the command line.
X(Note that systems supporting the #! notation invoke interpreters this way.)
X.Ip 3. 4 2
XPassed in implicitly via standard input.
XThis only works if there are no filename arguments\*(--to pass
Xarguments to a
X.I stdin
Xscript you must explicitly specify a \- for the script name.
X.PP
XAfter locating your script,
X.I perl
Xcompiles it to an internal form.
XIf the script is syntactically correct, it is executed.
X.Sh "Options"
XNote: on first reading this section may not make much sense to you.  It's here
Xat the front for easy reference.
X.PP
XA single-character option may be combined with the following option, if any.
XThis is particularly useful when invoking a script using the #! construct which
Xonly allows one argument.  Example:
X.nf
X
X.ne 2
X    #!/usr/bin/perl \-spi.bak    # same as \-s \-p \-i.bak
X    .\|.\|.
X
X.fi
XOptions include:
X.TP 5
X.BI \-0 digits
Xspecifies the record separator ($/) as an octal number.
XIf there are no digits, the null character is the separator.
XOther switches may precede or follow the digits.
XFor example, if you have a version of
X.I find
Xwhich can print filenames terminated by the null character, you can say this:
X.nf
X
X    find . \-name '*.bak' \-print0 | perl \-n0e unlink
X
X.fi
XThe special value 00 will cause Perl to slurp files in paragraph mode.
XThe value 0777 will cause Perl to slurp files whole since there is no
Xlegal character with that value.
X.TP 5
X.B \-a
Xturns on autosplit mode when used with a
X.B \-n
Xor
X.BR \-p .
XAn implicit split command to the @F array
Xis done as the first thing inside the implicit while loop produced by
Xthe
X.B \-n
Xor
X.BR \-p .
X.nf
X
X    perl \-ane \'print pop(@F), "\en";\'
X
Xis equivalent to
X
X    while (<>) {
X        @F = split(\' \');
X        print pop(@F), "\en";
X    }
X
X.fi
X.TP 5
X.B \-c
Xcauses
X.I perl
Xto check the syntax of the script and then exit without executing it.
X.TP 5
X.BI \-d
Xruns the script under the perl debugger.
XSee the section on Debugging.
X.TP 5
X.BI \-D number
Xsets debugging flags.
XTo watch how it executes your script, use
X.BR \-D14 .
X(This only works if debugging is compiled into your
X.IR perl .)
XAnother nice value is \-D1024, which lists your compiled syntax tree.
XAnd \-D512 displays compiled regular expressions.
X.TP 5
X.BI \-e " commandline"
Xmay be used to enter one line of script.
XMultiple
X.B \-e
Xcommands may be given to build up a multi-line script.
XIf
X.B \-e
Xis given,
X.I perl
Xwill not look for a script filename in the argument list.
X.TP 5
X.BI \-i extension
Xspecifies that files processed by the <> construct are to be edited
Xin-place.
XIt does this by renaming the input file, opening the output file by the
Xsame name, and selecting that output file as the default for print statements.
XThe extension, if supplied, is added to the name of the
Xold file to make a backup copy.
XIf no extension is supplied, no backup is made.
XSaying \*(L"perl \-p \-i.bak \-e "s/foo/bar/;" .\|.\|. \*(R" is the same as using
Xthe script:
X.nf
X
X.ne 2
X    #!/usr/bin/perl \-pi.bak
X    s/foo/bar/;
X
Xwhich is equivalent to
X
X.ne 14
X    #!/usr/bin/perl
X    while (<>) {
X        if ($ARGV ne $oldargv) {
X            rename($ARGV, $ARGV . \'.bak\');
X            open(ARGVOUT, ">$ARGV");
X            select(ARGVOUT);
X            $oldargv = $ARGV;
X        }
X        s/foo/bar/;
X    }
X    continue {
X        print;    # this prints to original filename
X    }
X    select(STDOUT);
X
X.fi
Xexcept that the
X.B \-i
Xform doesn't need to compare $ARGV to $oldargv to know when
Xthe filename has changed.
XIt does, however, use ARGVOUT for the selected filehandle.
XNote that
X.I STDOUT
Xis restored as the default output filehandle after the loop.
X.Sp
XYou can use eof to locate the end of each input file, in case you want
Xto append to each file, or reset line numbering (see example under eof).
X.TP 5
X.BI \-I directory
Xmay be used in conjunction with
X.B \-P
Xto tell the C preprocessor where to look for include files.
XBy default /usr/include and /usr/lib/perl are searched.
X.TP 5
X.BI \-l octnum
Xenables automatic line-ending processing.  It has two effects:
Xfirst, it automatically chops the line terminator when used with
X.B \-n
Xor
X.B \-p ,
Xand second, it assigns $\e to have the value of
X.I octnum
Xso that any print statements will have that line terminator added back on.  If
X.I octnum
Xis omitted, sets $\e to the current value of $/.
XFor instance, to trim lines to 80 columns:
X.nf
X
X    perl -lpe \'substr($_, 80) = ""\'
X
X.fi
XNote that the assignment $\e = $/ is done when the switch is processed,
Xso the input record separator can be different than the output record
Xseparator if the
X.B \-l
Xswitch is followed by a
X.B \-0
Xswitch:
X.nf
X
X    gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
X
X.fi
XThis sets $\e to newline and then sets $/ to the null character.
X.TP 5
X.B \-n
Xcauses
X.I perl
Xto assume the following loop around your script, which makes it iterate
Xover filename arguments somewhat like \*(L"sed \-n\*(R" or \fIawk\fR:
X.nf
X
X.ne 3
X    while (<>) {
X        .\|.\|.        # your script goes here
X    }
X
X.fi
XNote that the lines are not printed by default.
XSee
X.B \-p
Xto have lines printed.
XHere is an efficient way to delete all files older than a week:
X.nf
X
X    find . \-mtime +7 \-print | perl \-nle \'unlink;\'
X
X.fi
XThis is faster than using the \-exec switch of find because you don't have to
Xstart a process on every filename found.
X.TP 5
X.B \-p
Xcauses
X.I perl
Xto assume the following loop around your script, which makes it iterate
Xover filename arguments somewhat like \fIsed\fR:
X.nf
X
X.ne 5
X    while (<>) {
X        .\|.\|.        # your script goes here
X    } continue {
X        print;
X    }
X
X.fi
XNote that the lines are printed automatically.
XTo suppress printing use the
X.B \-n
Xswitch.
XA
X.B \-p
Xoverrides a
X.B \-n
Xswitch.
X.TP 5
X.B \-P
Xcauses your script to be run through the C preprocessor before
Xcompilation by
X.IR perl .
X(Since both comments and cpp directives begin with the # character,
Xyou should avoid starting comments with any words recognized
Xby the C preprocessor such as \*(L"if\*(R", \*(L"else\*(R" or \*(L"define\*(R".)
X.TP 5
X.B \-s
Xenables some rudimentary switch parsing for switches on the command line
Xafter the script name but before any filename arguments (or before a \-\|\-).
XAny switch found there is removed from @ARGV and sets the corresponding variable in the
X.I perl
Xscript.
XThe following script prints \*(L"true\*(R" if and only if the script is
Xinvoked with a \-xyz switch.
X.nf
X
X.ne 2
X    #!/usr/bin/perl \-s
X    if ($xyz) { print "true\en"; }
X
X.fi
X.TP 5
X.B \-S
Xmakes
X.I perl
Xuse the PATH environment variable to search for the script
X(unless the name of the script starts with a slash).
XTypically this is used to emulate #! startup on machines that don't
Xsupport #!, in the following manner:
X.nf
X
X    #!/usr/bin/perl
X    eval "exec /usr/bin/perl \-S $0 $*"
X        if $running_under_some_shell;
X
X.fi
XThe system ignores the first line and feeds the script to /bin/sh,
Xwhich proceeds to try to execute the
X.I perl
Xscript as a shell script.
XThe shell executes the second line as a normal shell command, and thus
Xstarts up the
X.I perl
Xinterpreter.
XOn some systems $0 doesn't always contain the full pathname,
Xso the
X.B \-S
Xtells
X.I perl
Xto search for the script if necessary.
XAfter
X.I perl
Xlocates the script, it parses the lines and ignores them because
Xthe variable $running_under_some_shell is never true.
XA better construct than $* would be ${1+"$@"}, which handles embedded spaces
Xand such in the filenames, but doesn't work if the script is being interpreted
Xby csh.
XIn order to start up sh rather than csh, some systems may have to replace the
X#! line with a line containing just
Xa colon, which will be politely ignored by perl.
XOther systems can't control that, and need a totally devious construct that
Xwill work under any of csh, sh or perl, such as the following:
X.nf
X
X.ne 3
X    eval '(exit $?0)' && eval 'exec /usr/bin/perl -S $0 ${1+"$@"}'
X    & eval 'exec /usr/bin/perl -S $0 $argv:q'
X        if 0;
X
X.fi
X.TP 5
X.B \-u
Xcauses
X.I perl
Xto dump core after compiling your script.
XYou can then take this core dump and turn it into an executable file
Xby using the undump program (not supplied).
XThis speeds startup at the expense of some disk space (which you can
Xminimize by stripping the executable).
X(Still, a "hello world" executable comes out to about 200K on my machine.)
XIf you are going to run your executable as a set-id program then you
Xshould probably compile it using taintperl rather than normal perl.
XIf you want to execute a portion of your script before dumping, use the
Xdump operator instead.
XNote: availability of undump is platform specific and may not be available
Xfor a specific port of perl.
X.TP 5
X.B \-U
Xallows
X.I perl
Xto do unsafe operations.
XCurrently the only \*(L"unsafe\*(R" operation is the unlinking of directories while
Xrunning as superuser.
X.TP 5
X.B \-v
Xprints the version and patchlevel of your
X.I perl
Xexecutable.
X.TP 5
X.B \-w
Xprints warnings about identifiers that are mentioned only once, and scalar
Xvariables that are used before being set.
XAlso warns about redefined subroutines, and references to undefined
Xfilehandles or filehandles opened readonly that you are attempting to
Xwrite on.
XAlso warns you if you use == on values that don't look like numbers, and if
Xyour subroutines recurse more than 100 deep.
X.TP 5
X.BI \-x directory
Xtells
X.I perl
Xthat the script is embedded in a message.
XLeading garbage will be discarded until the first line that starts
Xwith #! and contains the string "perl".
XAny meaningful switches on that line will be applied (but only one
Xgroup of switches, as with normal #! processing).
XIf a directory name is specified, Perl will switch to that directory
Xbefore running the script.
XThe
X.B \-x
Xswitch only controls the the disposal of leading garbage.
XThe script must be terminated with __END__ if there is trailing garbage
Xto be ignored (the script can process any or all of the trailing garbage
Xvia the DATA filehandle if desired).
X.Sh "Data Types and Objects"
X.PP
X.I Perl
Xhas three data types: scalars, arrays of scalars, and
Xassociative arrays of scalars.
XNormal arrays are indexed by number, and associative arrays by string.
X.PP
XThe interpretation of operations and values in perl sometimes
Xdepends on the requirements
Xof the context around the operation or value.
XThere are three major contexts: string, numeric and array.
XCertain operations return array values
Xin contexts wanting an array, and scalar values otherwise.
X(If this is true of an operation it will be mentioned in the documentation
Xfor that operation.)
XOperations which return scalars don't care whether the context is looking
Xfor a string or a number, but
Xscalar variables and values are interpreted as strings or numbers
Xas appropriate to the context.
XA scalar is interpreted as TRUE in the boolean sense if it is not the null
Xstring or 0.
XBooleans returned by operators are 1 for true and 0 or \'\' (the null
Xstring) for false.
X.PP
XThere are actually two varieties of null string: defined and undefined.
XUndefined null strings are returned when there is no real value for something,
Xsuch as when there was an error, or at end of file, or when you refer
Xto an uninitialized variable or element of an array.
XAn undefined null string may become defined the first time you access it, but
Xprior to that you can use the defined() operator to determine whether the
Xvalue is defined or not.
X.PP
XReferences to scalar variables always begin with \*(L'$\*(R', even when referring
Xto a scalar that is part of an array.
XThus:
X.nf
X
X.ne 3
X    $days    \h'|2i'# a simple scalar variable
X    $days[28]    \h'|2i'# 29th element of array @days
X    $days{\'Feb\'}\h'|2i'# one value from an associative array
X    $#days    \h'|2i'# last index of array @days
X
Xbut entire arrays or array slices are denoted by \*(L'@\*(R':
X
X    @days    \h'|2i'# ($days[0], $days[1],\|.\|.\|. $days[n])
X    @days[3,4,5]\h'|2i'# same as @days[3.\|.5]
X    @days{'a','c'}\h'|2i'# same as ($days{'a'},$days{'c'})
X
Xand entire associative arrays are denoted by \*(L'%\*(R':
X
X    %days    \h'|2i'# (key1, val1, key2, val2 .\|.\|.)
X.fi
X.PP
XAny of these eight constructs may serve as an lvalue,
Xthat is, may be assigned to.
X(It also turns out that an assignment is itself an lvalue in
Xcertain contexts\*(--see examples under s, tr and chop.)
XAssignment to a scalar evaluates the righthand side in a scalar context,
Xwhile assignment to an array or array slice evaluates the righthand side
Xin an array context.
X.PP
XYou may find the length of array @days by evaluating
X\*(L"$#days\*(R", as in
X.IR csh .
X(Actually, it's not the length of the array, it's the subscript of the last element, since there is (ordinarily) a 0th element.)
XAssigning to $#days changes the length of the array.
XShortening an array by this method does not actually destroy any values.
XLengthening an array that was previously shortened recovers the values that
Xwere in those elements.
XYou can also gain some measure of efficiency by preextending an array that
Xis going to get big.
X(You can also extend an array by assigning to an element that is off the
Xend of the array.
XThis differs from assigning to $#whatever in that intervening values
Xare set to null rather than recovered.)
XYou can truncate an array down to nothing by assigning the null list () to
Xit.
XThe following are exactly equivalent
X.nf
X
X    @whatever = ();
X    $#whatever = $[ \- 1;
X
X.fi
X.PP
XIf you evaluate an array in a scalar context, it returns the length of
Xthe array.
XThe following is always true:
X.nf
X
X    @whatever == $#whatever \- $[ + 1;
X
X.fi
X.PP
XMulti-dimensional arrays are not directly supported, but see the discussion
Xof the $; variable later for a means of emulating multiple subscripts with
Xan associative array.
XYou could also write a subroutine to turn multiple subscripts into a single
Xsubscript.
X.PP
XEvery data type has its own namespace.
XYou can, without fear of conflict, use the same name for a scalar variable,
Xan array, an associative array, a filehandle, a subroutine name, and/or
Xa label.
XSince variable and array references always start with \*(L'$\*(R', \*(L'@\*(R',
Xor \*(L'%\*(R', the \*(L"reserved\*(R" words aren't in fact reserved
Xwith respect to variable names.
X(They ARE reserved with respect to labels and filehandles, however, which
Xdon't have an initial special character.
XHint: you could say open(LOG,\'logfile\') rather than open(log,\'logfile\').
XUsing uppercase filehandles also improves readability and protects you
Xfrom conflict with future reserved words.)
XCase IS significant\*(--\*(L"FOO\*(R", \*(L"Foo\*(R" and \*(L"foo\*(R" are all
Xdifferent names.
XNames which start with a letter may also contain digits and underscores.
XNames which do not start with a letter are limited to one character,
Xe.g. \*(L"$%\*(R" or \*(L"$$\*(R".
X(Most of the one character names have a predefined significance to
X.IR perl .
XMore later.)
X.PP
XNumeric literals are specified in any of the usual floating point or
Xinteger formats:
X.nf
X
X.ne 5
X    12345
X    12345.67
X    .23E-10
X    0xffff    # hex
X    0377    # octal
X
X.fi
XString literals are delimited by either single or double quotes.
XThey work much like shell quotes:
Xdouble-quoted string literals are subject to backslash and variable
Xsubstitution; single-quoted strings are not (except for \e\' and \e\e).
XThe usual backslash rules apply for making characters such as newline, tab,
Xetc., as well as some more exotic forms:
X.nf
X
X    \et        tab
X    \en        newline
X    \er        return
X    \ef        form feed
X    \eb        backspace
X    \ea        alarm (bell)
X    \ee        escape
X    \e033        octal char
X    \ex1b        hex char
X    \ec[        control char
X    \el        lowercase next char
X    \eu        uppercase next char
X    \eL        lowercase till \eE
X    \eU        uppercase till \eE
X    \eE        end case modification
X
X.fi
XYou can also embed newlines directly in your strings, i.e. they can end on
Xa different line than they begin.
XThis is nice, but if you forget your trailing quote, the error will not be
Xreported until
X.I perl
Xfinds another line containing the quote character, which
Xmay be much further on in the script.
XVariable substitution inside strings is limited to scalar variables, normal
Xarray values, and array slices.
X(In other words, identifiers beginning with $ or @, followed by an optional
Xbracketed expression as a subscript.)
XThe following code segment prints out \*(L"The price is $100.\*(R"
X.nf
X
X.ne 2
X    $Price = \'$100\';\h'|3.5i'# not interpreted
X    print "The price is $Price.\e\|n";\h'|3.5i'# interpreted
X
X.fi
XNote that you can put curly brackets around the identifier to delimit it
Xfrom following alphanumerics.
XAlso note that a single quoted string must be separated from a preceding
Xword by a space, since single quote is a valid character in an identifier
X(see Packages).
X.PP
XTwo special literals are __LINE__ and __FILE__, which represent the current
Xline number and filename at that point in your program.
XThey may only be used as separate tokens; they will not be interpolated
Xinto strings.
XIn addition, the token __END__ may be used to indicate the logical end of the
Xscript before the actual end of file.
XAny following text is ignored (but may be read via the DATA filehandle).
XThe two control characters ^D and ^Z are synonyms for __END__.
X.PP
XA word that doesn't have any other interpretation in the grammar will be
Xtreated as if it had single quotes around it.
XFor this purpose, a word consists only of alphanumeric characters and underline,
Xand must start with an alphabetic character.
XAs with filehandles and labels, a bare word that consists entirely of
Xlowercase letters risks conflict with future reserved words, and if you
Xuse the
X.B \-w
Xswitch, Perl will warn you about any such words.
X.PP
XArray values are interpolated into double-quoted strings by joining all the
Xelements of the array with the delimiter specified in the $" variable,
Xspace by default.
X(Since in versions of perl prior to 3.0 the @ character was not a metacharacter
Xin double-quoted strings, the interpolation of @array, $array[EXPR],
X@array[LIST], $array{EXPR}, or @array{LIST} only happens if array is
Xreferenced elsewhere in the program or is predefined.)
XThe following are equivalent:
X.nf
X
X.ne 4
X    $temp = join($",@ARGV);
X    system "echo $temp";
X
X    system "echo @ARGV";
X
X.fi
XWithin search patterns (which also undergo double-quotish substitution)
Xthere is a bad ambiguity:  Is /$foo[bar]/ to be
Xinterpreted as /${foo}[bar]/ (where [bar] is a character class for the
Xregular expression) or as /${foo[bar]}/ (where [bar] is the subscript to
Xarray @foo)?
XIf @foo doesn't otherwise exist, then it's obviously a character class.
XIf @foo exists, perl takes a good guess about [bar], and is almost always right.
XIf it does guess wrong, or if you're just plain paranoid,
Xyou can force the correct interpretation with curly brackets as above.
X.PP
XA line-oriented form of quoting is based on the shell here-is syntax.
XFollowing a << you specify a string to terminate the quoted material, and all lines
Xfollowing the current line down to the terminating string are the value
Xof the item.
XThe terminating string may be either an identifier (a word), or some
Xquoted text.
XIf quoted, the type of quotes you use determines the treatment of the text,
Xjust as in regular quoting.
XAn unquoted identifier works like double quotes.
XThere must be no space between the << and the identifier.
X(If you put a space it will be treated as a null identifier, which is
Xvalid, and matches the first blank line\*(--see Merry Christmas example below.)
XThe terminating string must appear by itself (unquoted and with no surrounding
Xwhitespace) on the terminating line.
X.nf
X
X    print <<EOF;        # same as above
XThe price is $Price.
XEOF
X
X    print <<"EOF";        # same as above
XThe price is $Price.
XEOF
X
X    print << x 10;        # null identifier is delimiter
XMerry Christmas!
X
X    print <<`EOC`;        # execute commands
Xecho hi there
Xecho lo there
XEOC
X
X    print <<foo, <<bar;    # you can stack them
XI said foo.
Xfoo
XI said bar.
Xbar
X
X.fi
XArray literals are denoted by separating individual values by commas, and
Xenclosing the list in parentheses:
X.nf
X
X    (LIST)
X
X.fi
XIn a context not requiring an array value, the value of the array literal
Xis the value of the final element, as in the C comma operator.
XFor example,
X.nf
X
X.ne 4
X    @foo = (\'cc\', \'\-E\', $bar);
X
Xassigns the entire array value to array foo, but
X
X    $foo = (\'cc\', \'\-E\', $bar);
X
X.fi
Xassigns the value of variable bar to variable foo.
XNote that the value of an actual array in a scalar context is the length
Xof the array; the following assigns to $foo the value 3:
X.nf
X
X.ne 2
X    @foo = (\'cc\', \'\-E\', $bar);
X    $foo = @foo;        # $foo gets 3
X
X.fi
XYou may have an optional comma before the closing parenthesis of an
Xarray literal, so that you can say:
X.nf
X
X    @foo = (
X    1,
X    2,
X    3,
X    );
X
X.fi
XWhen a LIST is evaluated, each element of the list is evaluated in
Xan array context, and the resulting array value is interpolated into LIST
Xjust as if each individual element were a member of LIST.  Thus arrays
Xlose their identity in a LIST\*(--the list
X
X    (@foo,@bar,&SomeSub)
X
Xcontains all the elements of @foo followed by all the elements of @bar,
Xfollowed by all the elements returned by the subroutine named SomeSub.
X.PP
XA list value may also be subscripted like a normal array.
XExamples:
X.nf
X
X    $time = (stat($file))[8];    # stat returns array value
X    $digit = ('a','b','c','d','e','f')[$digit-10];
X    return (pop(@foo),pop(@foo))[0];
X
X.fi
X.PP
XArray lists may be assigned to if and only if each element of the list
Xis an lvalue:
X.nf
X
X    ($a, $b, $c) = (1, 2, 3);
X
X    ($map{\'red\'}, $map{\'blue\'}, $map{\'green\'}) = (0x00f, 0x0f0, 0xf00);
X
XThe final element may be an array or an associative array:
X
X    ($a, $b, @rest) = split;
X    local($a, $b, %rest) = @_;
X
X.fi
XYou can actually put an array anywhere in the list, but the first array
Xin the list will soak up all the values, and anything after it will get
Xa null value.
XThis may be useful in a local().
X.PP
XAn associative array literal contains pairs of values to be interpreted
Xas a key and a value:
X.nf
X
X.ne 2
X    # same as map assignment above
X    %map = ('red',0x00f,'blue',0x0f0,'green',0xf00);
X
X.fi
XArray assignment in a scalar context returns the number of elements
Xproduced by the expression on the right side of the assignment:
X.nf
X
X    $x = (($foo,$bar) = (3,2,1));    # set $x to 3, not 2
X
X.fi
X.PP
XThere are several other pseudo-literals that you should know about.
XIf a string is enclosed by backticks (grave accents), it first undergoes
Xvariable substitution just like a double quoted string.
XIt is then interpreted as a command, and the output of that command
Xis the value of the pseudo-literal, like in a shell.
XIn a scalar context, a single string consisting of all the output is
Xreturned.
XIn an array context, an array of values is returned, one for each line
Xof output.
X(You can set $/ to use a different line terminator.)
XThe command is executed each time the pseudo-literal is evaluated.
XThe status value of the command is returned in $? (see Predefined Names
Xfor the interpretation of $?).
XUnlike in \f2csh\f1, no translation is done on the return
Xdata\*(--newlines remain newlines.
XUnlike in any of the shells, single quotes do not hide variable names
Xin the command from interpretation.
XTo pass a $ through to the shell you need to hide it with a backslash.
X.PP
XEvaluating a filehandle in angle brackets yields the next line
Xfrom that file (newline included, so it's never false until EOF, at
Xwhich time an undefined value is returned).
XOrdinarily you must assign that value to a variable,
Xbut there is one situation where an automatic assignment happens.
XIf (and only if) the input symbol is the only thing inside the conditional of a
X.I while
Xloop, the value is
Xautomatically assigned to the variable \*(L"$_\*(R".
X(This may seem like an odd thing to you, but you'll use the construct
Xin almost every
X.I perl
Xscript you write.)
XAnyway, the following lines are equivalent to each other:
X.nf
X
X.ne 5
X    while ($_ = <STDIN>) { print; }
X    while (<STDIN>) { print; }
X    for (\|;\|<STDIN>;\|) { print; }
X    print while $_ = <STDIN>;
X    print while <STDIN>;
X
X.fi
XThe filehandles
X.IR STDIN ,
X.I STDOUT
Xand
X.I STDERR
Xare predefined.
X(The filehandles
X.IR stdin ,
X.I stdout
Xand
X.I stderr
Xwill also work except in packages, where they would be interpreted as
Xlocal identifiers rather than global.)
XAdditional filehandles may be created with the
X.I open
Xfunction.
X.PP
XIf a <FILEHANDLE> is used in a context that is looking for an array, an array
Xconsisting of all the input lines is returned, one line per array element.
XIt's easy to make a LARGE data space this way, so use with care.
X.PP
XThe null filehandle <> is special and can be used to emulate the behavior of
X\fIsed\fR and \fIawk\fR.
XInput from <> comes either from standard input, or from each file listed on
Xthe command line.
XHere's how it works: the first time <> is evaluated, the ARGV array is checked,
Xand if it is null, $ARGV[0] is set to \'-\', which when opened gives you standard
Xinput.
XThe ARGV array is then processed as a list of filenames.
XThe loop
X.nf
X
X.ne 3
X    while (<>) {
X        .\|.\|.            # code for each line
X    }
X
X.ne 10
Xis equivalent to
X
X    unshift(@ARGV, \'\-\') \|if \|$#ARGV < $[;
X    while ($ARGV = shift) {
X        open(ARGV, $ARGV);
X        while (<ARGV>) {
X            .\|.\|.        # code for each line
X        }
X    }
X
X.fi
Xexcept that it isn't as cumbersome to say.
XIt really does shift array ARGV and put the current filename into
Xvariable ARGV.
XIt also uses filehandle ARGV internally.
XYou can modify @ARGV before the first <> as long as you leave the first
Xfilename at the beginning of the array.
XLine numbers ($.) continue as if the input was one big happy file.
X(But see example under eof for how to reset line numbers on each file.)
X.PP
X.ne 5
XIf you want to set @ARGV to your own list of files, go right ahead.
XIf you want to pass switches into your script, you can
Xput a loop on the front like this:
X.nf
X
X.ne 10
X    while ($_ = $ARGV[0], /\|^\-/\|) {
X        shift;
X        last if /\|^\-\|\-$\|/\|;
X        /\|^\-D\|(.*\|)/ \|&& \|($debug = $1);
X        /\|^\-v\|/ \|&& \|$verbose++;
X        .\|.\|.        # other switches
X    }
X    while (<>) {
X        .\|.\|.        # code for each line
X    }
X
X.fi
XThe <> symbol will return FALSE only once.
XIf you call it again after this it will assume you are processing another
X@ARGV list, and if you haven't set @ARGV, will input from
X.IR STDIN .
X.PP
XIf the string inside the angle brackets is a reference to a scalar variable
X(e.g. <$foo>),
Xthen that variable contains the name of the filehandle to input from.
X.PP
XIf the string inside angle brackets is not a filehandle, it is interpreted
Xas a filename pattern to be globbed, and either an array of filenames or the
Xnext filename in the list is returned, depending on context.
XOne level of $ interpretation is done first, but you can't say <$foo>
Xbecause that's an indirect filehandle as explained in the previous
Xparagraph.
XYou could insert curly brackets to force interpretation as a
Xfilename glob: <${foo}>.
XExample:
X.nf
X
X.ne 3
X    while (<*.c>) {
X        chmod 0644, $_;
X    }
X
Xis equivalent to
X
X.ne 5
X    open(foo, "echo *.c | tr \-s \' \et\er\ef\' \'\e\e012\e\e012\e\e012\e\e012\'|");
X    while (<foo>) {
X        chop;
X        chmod 0644, $_;
X    }
X
X.fi
XIn fact, it's currently implemented that way.
X(Which means it will not work on filenames with spaces in them unless
Xyou have /bin/csh on your machine.)
XOf course, the shortest way to do the above is:
X.nf
X
X    chmod 0644, <*.c>;
X
X.fi
X.Sh "Syntax"
X.PP
XA
X.I perl
Xscript consists of a sequence of declarations and commands.
XThe only things that need to be declared in
X.I perl
Xare report formats and subroutines.
XSee the sections below for more information on those declarations.
XAll uninitialized user-created objects are assumed to
Xstart with a null or 0 value until they
Xare defined by some explicit operation such as assignment.
XThe sequence of commands is executed just once, unlike in
X.I sed
Xand
X.I awk
Xscripts, where the sequence of commands is executed for each input line.
XWhile this means that you must explicitly loop over the lines of your input file
X(or files), it also means you have much more control over which files and which
Xlines you look at.
X(Actually, I'm lying\*(--it is possible to do an implicit loop with either the
X.B \-n
Xor
X.B \-p
Xswitch.)
X.PP
XA declaration can be put anywhere a command can, but has no effect on the
Xexecution of the primary sequence of commands\*(--declarations all take effect
Xat compile time.
XTypically all the declarations are put at the beginning or the end of the script.
X.PP
X.I Perl
Xis, for the most part, a free-form language.
X(The only exception to this is format declarations, for fairly obvious reasons.)
XComments are indicated by the # character, and extend to the end of the line.
XIf you attempt to use /* */ C comments, it will be interpreted either as
Xdivision or pattern matching, depending on the context.
XSo don't do that.
X.Sh "Compound statements"
XIn
X.IR perl ,
Xa sequence of commands may be treated as one command by enclosing it
Xin curly brackets.
XWe will call this a BLOCK.
X.PP
XThe following compound commands may be used to control flow:
X.nf
X
X.ne 4
X    if (EXPR) BLOCK
X    if (EXPR) BLOCK else BLOCK
X    if (EXPR) BLOCK elsif (EXPR) BLOCK .\|.\|. else BLOCK
X    LABEL while (EXPR) BLOCK
X    LABEL while (EXPR) BLOCK continue BLOCK
X    LABEL for (EXPR; EXPR; EXPR) BLOCK
X    LABEL foreach VAR (ARRAY) BLOCK
X    LABEL BLOCK continue BLOCK
X
X.fi
XNote that, unlike C and Pascal, these are defined in terms of BLOCKs, not
Xstatements.
XThis means that the curly brackets are \fIrequired\fR\*(--no dangling statements allowed.
XIf you want to write conditionals without curly brackets there are several
Xother ways to do it.
XThe following all do the same thing:
X.nf
X
X.ne 5
X    if (!open(foo)) { die "Can't open $foo: $!"; }
X    die "Can't open $foo: $!" unless open(foo);
X    open(foo) || die "Can't open $foo: $!";    # foo or bust!
X    open(foo) ? \'hi mom\' : die "Can't open $foo: $!";
X                # a bit exotic, that last one
X
X.fi
X.PP
XThe
X.I if
Xstatement is straightforward.
XSince BLOCKs are always bounded by curly brackets, there is never any
Xambiguity about which
X.I if
Xan
X.I else
Xgoes with.
XIf you use
X.I unless
Xin place of
X.IR if ,
Xthe sense of the test is reversed.
X.PP
XThe
X.I while
Xstatement executes the block as long as the expression is true
X(does not evaluate to the null string or 0).
XThe LABEL is optional, and if present, consists of an identifier followed by
Xa colon.
XThe LABEL identifies the loop for the loop control statements
X.IR next ,
X.IR last ,
Xand
X.I redo
X(see below).
XIf there is a
X.I continue
XBLOCK, it is always executed just before
Xthe conditional is about to be evaluated again, similarly to the third part
Xof a
X.I for
Xloop in C.
XThus it can be used to increment a loop variable, even when the loop has
Xbeen continued via the
X.I next
Xstatement (similar to the C \*(L"continue\*(R" statement).
X.PP
XIf the word
X.I while
Xis replaced by the word
X.IR until ,
Xthe sense of the test is reversed, but the conditional is still tested before
Xthe first iteration.
X.PP
XIn either the
X.I if
Xor the
X.I while
Xstatement, you may replace \*(L"(EXPR)\*(R" with a BLOCK, and the conditional
Xis true if the value of the last command in that block is true.
X.PP
XThe
X.I for
Xloop works exactly like the corresponding
X.I while
Xloop:
X.nf
X
X.ne 12
X    for ($i = 1; $i < 10; $i++) {
X        .\|.\|.
X    }
X
Xis the same as
X
X    $i = 1;
X    while ($i < 10) {
X        .\|.\|.
X    } continue {
X        $i++;
X    }
X.fi
X.PP
XThe foreach loop iterates over a normal array value and sets the variable
XVAR to be each element of the array in turn.
XThe variable is implicitly local to the loop, and regains its former value
Xupon exiting the loop.
XThe \*(L"foreach\*(R" keyword is actually identical to the \*(L"for\*(R" keyword,
Xso you can use \*(L"foreach\*(R" for readability or \*(L"for\*(R" for brevity.
XIf VAR is omitted, $_ is set to each value.
XIf ARRAY is an actual array (as opposed to an expression returning an array
Xvalue), you can modify each element of the array
Xby modifying VAR inside the loop.
XExamples:
X.nf
X
X.ne 5
X    for (@ary) { s/foo/bar/; }
X
X    foreach $elem (@elements) {
X        $elem *= 2;
X    }
X
X.ne 3
X    for ((10,9,8,7,6,5,4,3,2,1,\'BOOM\')) {
X        print $_, "\en"; sleep(1);
X    }
X
X    for (1..15) { print "Merry Christmas\en"; }
X
X.ne 3
X    foreach $item (split(/:[\e\e\en:]*/, $ENV{\'TERMCAP\'})) {
X        print "Item: $item\en";
X    }
X
X.fi
X.PP
XThe BLOCK by itself (labeled or not) is equivalent to a loop that executes
Xonce.
XThus you can use any of the loop control statements in it to leave or
Xrestart the block.
XThe
X.I continue
Xblock is optional.
XThis construct is particularly nice for doing case structures.
X.nf
X
X.ne 6
X    foo: {
X        if (/^abc/) { $abc = 1; last foo; }
X        if (/^def/) { $def = 1; last foo; }
X        if (/^xyz/) { $xyz = 1; last foo; }
X        $nothing = 1;
X    }
X
X.fi
XThere is no official switch statement in perl, because there
Xare already several ways to write the equivalent.
XIn addition to the above, you could write
X.nf
X
X.ne 6
X    foo: {
X        $abc = 1, last foo  if /^abc/;
X        $def = 1, last foo  if /^def/;
X        $xyz = 1, last foo  if /^xyz/;
X        $nothing = 1;
X    }
X
Xor
X
X.ne 6
X    foo: {
X        /^abc/ && do { $abc = 1; last foo; };
X        /^def/ && do { $def = 1; last foo; };
X        /^xyz/ && do { $xyz = 1; last foo; };
X        $nothing = 1;
X    }
X
Xor
X
X.ne 6
X    foo: {
X        /^abc/ && ($abc = 1, last foo);
X        /^def/ && ($def = 1, last foo);
X        /^xyz/ && ($xyz = 1, last foo);
X        $nothing = 1;
X    }
X
Xor even
X
X.ne 8
X    if (/^abc/)
X        { $abc = 1; }
X    elsif (/^def/)
X        { $def = 1; }
X    elsif (/^xyz/)
X        { $xyz = 1; }
X    else
X        {$nothing = 1;}
X
X.fi
XAs it happens, these are all optimized internally to a switch structure,
Xso perl jumps directly to the desired statement, and you needn't worry
Xabout perl executing a lot of unnecessary statements when you have a string
Xof 50 elsifs, as long as you are testing the same simple scalar variable
Xusing ==, eq, or pattern matching as above.
X(If you're curious as to whether the optimizer has done this for a particular
Xcase statement, you can use the \-D1024 switch to list the syntax tree
Xbefore execution.)
X.Sh "Simple statements"
XThe only kind of simple statement is an expression evaluated for its side
Xeffects.
XEvery expression (simple statement) must be terminated with a semicolon.
XNote that this is like C, but unlike Pascal (and
X.IR awk ).
X.PP
XAny simple statement may optionally be followed by a
Xsingle modifier, just before the terminating semicolon.
XThe possible modifiers are:
X.nf
X
X.ne 4
X    if EXPR
X    unless EXPR
X    while EXPR
X    until EXPR
X
X.fi
XThe
X.I if
Xand
X.I unless
Xmodifiers have the expected semantics.
XThe
X.I while
Xand
X.I until
Xmodifiers also have the expected semantics (conditional evaluated first),
Xexcept when applied to a do-BLOCK or a do-SUBROUTINE command,
Xin which case the block executes once before the conditional is evaluated.
XThis is so that you can write loops like:
X.nf
X
X.ne 4
X    do {
X        $_ = <STDIN>;
X        .\|.\|.
X    } until $_ \|eq \|".\|\e\|n";
X
X.fi
X(See the
X.I do
Xoperator below.  Note also that the loop control commands described later will
XNOT work in this construct, since modifiers don't take loop labels.
XSorry.)
X.Sh "Expressions"
XSince
X.I perl
Xexpressions work almost exactly like C expressions, only the differences
Xwill be mentioned here.
X.PP
XHere's what
X.I perl
Xhas that C doesn't:
X.Ip ** 8 2
XThe exponentiation operator.
X.Ip **= 8
XThe exponentiation assignment operator.
X.Ip (\|) 8 3
XThe null list, used to initialize an array to null.
X.Ip . 8
XConcatenation of two strings.
X.Ip .= 8
XThe concatenation assignment operator.
X.Ip eq 8
XString equality (== is numeric equality).
XFor a mnemonic just think of \*(L"eq\*(R" as a string.
X(If you are used to the
X.I awk
Xbehavior of using == for either string or numeric equality
Xbased on the current form of the comparands, beware!
XYou must be explicit here.)
X.Ip ne 8
XString inequality (!= is numeric inequality).
X.Ip lt 8
XString less than.
X.Ip gt 8
XString greater than.
X.Ip le 8
XString less than or equal.
X.Ip ge 8
XString greater than or equal.
X.Ip cmp 8
XString comparison, returning -1, 0, or 1.
X.Ip <=> 8
XNumeric comparison, returning -1, 0, or 1.
X.Ip =~ 8 2
XCertain operations search or modify the string \*(L"$_\*(R" by default.
XThis operator makes that kind of operation work on some other string.
XThe right argument is a search pattern, substitution, or translation.
XThe left argument is what is supposed to be searched, substituted, or
Xtranslated instead of the default \*(L"$_\*(R".
XThe return value indicates the success of the operation.
X(If the right argument is an expression other than a search pattern,
Xsubstitution, or translation, it is interpreted as a search pattern
Xat run time.
XThis is less efficient than an explicit search, since the pattern must
Xbe compiled every time the expression is evaluated.)
XThe precedence of this operator is lower than unary minus and autoincrement/decrement, but higher than everything else.
X.Ip !~ 8
XJust like =~ except the return value is negated.
X.Ip x 8
XThe repetition operator.
XReturns a string consisting of the left operand repeated the
Xnumber of times specified by the right operand.
XIn an array context, if the left operand is a list in parens, it repeats
Xthe list.
X.nf
X
X    print \'\-\' x 80;        # print row of dashes
X    print \'\-\' x80;        # illegal, x80 is identifier
X
X    print "\et" x ($tab/8), \' \' x ($tab%8);    # tab over
X
X    @ones = (1) x 80;        # an array of 80 1's
X    @ones = (5) x @ones;        # set all elements to 5
X
X.fi
X.Ip x= 8
XThe repetition assignment operator.
XOnly works on scalars.
X.Ip .\|. 8
XThe range operator, which is really two different operators depending
Xon the context.
XIn an array context, returns an array of values counting (by ones)
Xfrom the left value to the right value.
XThis is useful for writing \*(L"for (1..10)\*(R" loops and for doing
Xslice operations on arrays.
X.Sp
XIn a scalar context, .\|. returns a boolean value.
XThe operator is bistable, like a flip-flop..
XEach .\|. operator maintains its own boolean state.
XIt is false as long as its left operand is false.
XOnce the left operand is true, the range operator stays true
Xuntil the right operand is true,
XAFTER which the range operator becomes false again.
X(It doesn't become false till the next time the range operator is evaluated.
XIt can become false on the same evaluation it became true, but it still returns
Xtrue once.)
XThe right operand is not evaluated while the operator is in the \*(L"false\*(R" state,
Xand the left operand is not evaluated while the operator is in the \*(L"true\*(R" state.
XThe scalar .\|. operator is primarily intended for doing line number ranges
Xafter
Xthe fashion of \fIsed\fR or \fIawk\fR.
XThe precedence is a little lower than || and &&.
XThe value returned is either the null string for false, or a sequence number
X(beginning with 1) for true.
XThe sequence number is reset for each range encountered.
XThe final sequence number in a range has the string \'E0\' appended to it, which
Xdoesn't affect its numeric value, but gives you something to search for if you
Xwant to exclude the endpoint.
XYou can exclude the beginning point by waiting for the sequence number to be
Xgreater than 1.
XIf either operand of scalar .\|. is static, that operand is implicitly compared
Xto the $. variable, the current line number.
XExamples:
X.nf
X
X.ne 6
XAs a scalar operator:
X    if (101 .\|. 200) { print; }    # print 2nd hundred lines
X
X    next line if (1 .\|. /^$/);    # skip header lines
X
X    s/^/> / if (/^$/ .\|. eof());    # quote body
X
X.ne 4
XAs an array operator:
X    for (101 .\|. 200) { print; }    # print $_ 100 times
X
X    @foo = @foo[$[ .\|. $#foo];    # an expensive no-op
X    @foo = @foo[$#foo-4 .\|. $#foo];    # slice last 5 items
X
X.fi
X.Ip \-x 8
XA file test.
XThis unary operator takes one argument, either a filename or a filehandle,
Xand tests the associated file to see if something is true about it.
XIf the argument is omitted, tests $_, except for \-t, which tests
X.IR STDIN .
XIt returns 1 for true and \'\' for false, or the undefined value if the
Xfile doesn't exist.
XPrecedence is higher than logical and relational operators, but lower than
Xarithmetic operators.
XThe operator may be any of:
X.nf
X    \-r    File is readable by effective uid.
X    \-w    File is writable by effective uid.
X    \-x    File is executable by effective uid.
X    \-o    File is owned by effective uid.
X    \-R    File is readable by real uid.
X    \-W    File is writable by real uid.
X    \-X    File is executable by real uid.
X    \-O    File is owned by real uid.
X    \-e    File exists.
X    \-z    File has zero size.
X    \-s    File has non-zero size (returns size).
X    \-f    File is a plain file.
X    \-d    File is a directory.
X    \-l    File is a symbolic link.
X    \-p    File is a named pipe (FIFO).
X    \-S    File is a socket.
X    \-b    File is a block special file.
X    \-c    File is a character special file.
X    \-u    File has setuid bit set.
X    \-g    File has setgid bit set.
X    \-k    File has sticky bit set.
X    \-t    Filehandle is opened to a tty.
X    \-T    File is a text file.
X    \-B    File is a binary file (opposite of \-T).
X    \-M    Age of file in days when script started.
X    \-A    Same for access time.
X    \-C    Same for inode change time.
X
X.fi
XThe interpretation of the file permission operators \-r, \-R, \-w, \-W, \-x and \-X
Xis based solely on the mode of the file and the uids and gids of the user.
XThere may be other reasons you can't actually read, write or execute the file.
XAlso note that, for the superuser, \-r, \-R, \-w and \-W always return 1, and
X\-x and \-X return 1 if any execute bit is set in the mode.
XScripts run by the superuser may thus need to do a stat() in order to determine
Xthe actual mode of the file, or temporarily set the uid to something else.
X.Sp
XExample:
X.nf
X.ne 7
X
X    while (<>) {
X        chop;
X        next unless \-f $_;    # ignore specials
X        .\|.\|.
X    }
X
X.fi
XNote that \-s/a/b/ does not do a negated substitution.
XSaying \-exp($foo) still works as expected, however\*(--only single letters
Xfollowing a minus are interpreted as file tests.
X.Sp
XThe \-T and \-B switches work as follows.
XThe first block or so of the file is examined for odd characters such as
Xstrange control codes or metacharacters.
XIf too many odd characters (>10%) are found, it's a \-B file, otherwise it's a \-T file.
XAlso, any file containing null in the first block is considered a binary file.
XIf \-T or \-B is used on a filehandle, the current stdio buffer is examined
Xrather than the first block.
XBoth \-T and \-B return TRUE on a null file, or a file at EOF when testing
Xa filehandle.
X.PP
XIf any of the file tests (or either stat operator) are given the special
Xfilehandle consisting of a solitary underline, then the stat structure
Xof the previous file test (or stat operator) is used, saving a system
Xcall.
X(This doesn't work with \-t, and you need to remember that lstat and -l
Xwill leave values in the stat structure for the symbolic link, not the
Xreal file.)
XExample:
X.nf
X
X    print "Can do.\en" if -r $a || -w _ || -x _;
X
X.ne 9
X    stat($filename);
X    print "Readable\en" if -r _;
X    print "Writable\en" if -w _;
X    print "Executable\en" if -x _;
X    print "Setuid\en" if -u _;
X    print "Setgid\en" if -g _;
X    print "Sticky\en" if -k _;
X    print "Text\en" if -T _;
X    print "Binary\en" if -B _;
X
X.fi
X.PP
XHere is what C has that
X.I perl
Xdoesn't:
X.Ip "unary &" 12
XAddress-of operator.
X.Ip "unary *" 12
XDereference-address operator.
X.Ip "(TYPE)" 12
XType casting operator.
X.PP
XLike C,
X.I perl
Xdoes a certain amount of expression evaluation at compile time, whenever
Xit determines that all of the arguments to an operator are static and have
Xno side effects.
XIn particular, string concatenation happens at compile time between literals that don't do variable substitution.
XBackslash interpretation also happens at compile time.
XYou can say
X.nf
X
X.ne 2
X    \'Now is the time for all\' . "\|\e\|n" .
X    \'good men to come to.\'
X
X.fi
Xand this all reduces to one string internally.
X.PP
XThe autoincrement operator has a little extra built-in magic to it.
XIf you increment a variable that is numeric, or that has ever been used in
Xa numeric context, you get a normal increment.
XIf, however, the variable has only been used in string contexts since it
Xwas set, and has a value that is not null and matches the
Xpattern /^[a\-zA\-Z]*[0\-9]*$/, the increment is done
Xas a string, preserving each character within its range, with carry:
X.nf
X
X    print ++($foo = \'99\');    # prints \*(L'100\*(R'
X    print ++($foo = \'a0\');    # prints \*(L'a1\*(R'
X    print ++($foo = \'Az\');    # prints \*(L'Ba\*(R'
X    print ++($foo = \'zz\');    # prints \*(L'aaa\*(R'
X
X.fi
XThe autodecrement is not magical.
X.PP
XThe range operator (in an array context) makes use of the magical
Xautoincrement algorithm if the minimum and maximum are strings.
XYou can say
X
X    @alphabet = (\'A\' .. \'Z\');
X
Xto get all the letters of the alphabet, or
X
X    $hexdigit = (0 .. 9, \'a\' .. \'f\')[$num & 15];
X
Xto get a hexadecimal digit, or
X
X    @z2 = (\'01\' .. \'31\');  print @z2[$mday];
X
Xto get dates with leading zeros.
X(If the final value specified is not in the sequence that the magical increment
Xwould produce, the sequence goes until the next value would be longer than
Xthe final value specified.)
X.PP
XThe || and && operators differ from C's in that, rather than returning 0 or 1,
Xthey return the last value evaluated.
XThus, a portable way to find out the home directory might be:
X.nf
X
X    $home = $ENV{'HOME'} || $ENV{'LOGDIR'} ||
X        (getpwuid($<))[7] || die "You're homeless!\en";
X
X.fi
X''' Beginning of part 2
X''' $RCSfile: perl.man,v $$Revision: 4.0.1.1 $$Date: 91/04/11 17:50:44 $
X'''
X''' $Log:    perl.man,v $
X''' Revision 4.0.1.1  91/04/11  17:50:44  lwall
X''' patch1: fixed some typos
X'''
X''' Revision 4.0  91/03/20  01:38:08  lwall
X''' 4.0 baseline.
X'''
X''' Revision 3.0.1.11  91/01/11  18:17:08  lwall
X''' patch42: fixed some man page entries
!STUFFY!FUNK!
echo " "
echo "End of kit 2 (of 36)"
cat /dev/null >kit2isdone
run=''
config=''
for iskit in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36; do
    if test -f kit${iskit}isdone; then
    run="$run $iskit"
    else
    todo="$todo $iskit"
    fi
done
case $todo in
    '')
    echo "You have run all your kits.  Please read README and then type Configure."
    for combo in *:AA; do
        if test -f "$combo"; then
        realfile=`basename $combo :AA`
        cat $realfile:[A-Z][A-Z] >$realfile
        rm -rf $realfile:[A-Z][A-Z]
        fi
    done
    rm -rf kit*isdone
    chmod 755 Configure
    ;;
    *)  echo "You have run$run."
    echo "You still need to run$todo."
    ;;
esac
: Someone might mail this, so...
exit

exit 0 # Just in case...
--
Kent Landfield                   INTERNET: [e-mail]
Sterling Software, IMD           UUCP:     uunet!sparky!kent
Phone:    [phone]         FAX:      [phone]
Please send comp.sources.misc-related mail to [e-mail].