IRIX Base Documentation 1998 November/IRIX 6.5.2 Base Documentation November 1998.img/usr/share/catman/u_man/cat1/perlfunc.z/perlfunc

Text File | 1998-10-30 | 216KB | 5,281 lines

PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



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     perlfunc - Perl builtin functions

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     The functions in this section can serve as terms in an expression.  They
     fall into two major categories: list operators and named unary operators.
     These differ in their precedence relationship with a following comma.
     (See the precedence table in the _p_e_r_l_o_p manpage.)  List operators take
     more than one argument, while unary operators can never take more than
     one argument.  Thus, a comma terminates the argument of a unary operator,
     but merely separates the arguments of a list operator.  A unary operator
     generally provides a scalar context to its argument, while a list
     operator may provide either scalar and list contexts for its arguments.
     If it does both, the scalar arguments will be first, and the list
     argument will follow.  (Note that there can ever be only one list
     argument.)  For instance, _s_p_l_i_c_e() has three scalar arguments followed by
     a list.

     In the syntax descriptions that follow, list operators that expect a list
     (and provide list context for the elements of the list) are shown with
     LIST as an argument.  Such a list may consist of any combination of
     scalar arguments or list values; the list 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 list value.  Elements of the
     LIST should be separated by commas.

     Any function in the list below may be used either with or without
     parentheses around its arguments.  (The syntax descriptions omit the
     parentheses.)  If you use the parentheses, the simple (but occasionally
     surprising) rule is this: It _L_O_O_K_S like a function, therefore it _I_S a
     function, and precedence doesn't matter.  Otherwise it's a list operator
     or unary operator, and precedence does matter.  And whitespace between
     the function and left parenthesis doesn't count--so you need to be
     careful sometimes:

         print 1+2+4;        # Prints 7.
         print(1+2) + 4;     # Prints 3.
         print (1+2)+4;      # Also prints 3!
         print +(1+2)+4;     # Prints 7.
         print ((1+2)+4);    # Prints 7.

     If you run Perl with the ----wwww switch it can warn you about this.  For
     example, the third line above produces:

         print (...) interpreted as function at - line 1.
         Useless use of integer addition in void context at - line 1.

     For functions that can be used in either a scalar or list context,
     nonabortive failure is generally indicated in a scalar context by
     returning the undefined value, and in a list context by returning the
     null list.




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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



     Remember the following rule:

     _T_H_E_R_E _I_S _N_O _G_E_N_E_R_A_L _R_U_L_E _F_O_R _C_O_N_V_E_R_T_I_N_G _A _L_I_S_T _I_N_T_O _A _S_C_A_L_A_R!

     Each operator and function decides which sort of value it would be most
     appropriate to return in a scalar context.  Some operators return the
     length of the list that would have been returned in a list 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.

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     Here are Perl's functions (including things that look like functions,
     like some of the keywords and named operators) arranged by category.
     Some functions appear in more than one place.

     Functions for SCALARs or strings
          chomp, chop, chr, crypt, hex, index, lc, lcfirst, length, oct, ord,
          pack, q/STRING/, qq/STRING/, reverse, rindex, sprintf, substr,
          tr///, uc, ucfirst, y///

     Regular expressions and pattern matching
          m//, pos, quotemeta, s///, split, study

     Numeric functions
          abs, atan2, cos, exp, hex, int, log, oct, rand, sin, sqrt, srand

     Functions for real @ARRAYs
          pop, push, shift, splice, unshift

     Functions for list data
          grep, join, map, qw/STRING/, reverse, sort, unpack

     Functions for real %HASHes
          delete, each, exists, keys, values

     Input and output functions
          binmode, close, closedir, dbmclose, dbmopen, die, eof, fileno,
          flock, format, getc, print, printf, read, readdir, rewinddir, seek,
          seekdir, select, syscall, sysread, sysseek, syswrite, tell, telldir,
          truncate, warn, write

     Functions for fixed length data or records
          pack, read, syscall, sysread, syswrite, unpack, vec

     Functions for filehandles, files, or directories
          -_X, chdir, chmod, chown, chroot, fcntl, glob, ioctl, link, lstat,
          mkdir, open, opendir, readlink, rename, rmdir, stat, symlink, umask,
          unlink, utime




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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



     Keywords related to the control flow of your perl program
          caller, continue, die, do, dump, eval, exit, goto, last, next, redo,
          return, sub, wantarray

     Keywords related to scoping
          caller, import, local, my, package, use

     Miscellaneous functions
          defined, dump, eval, formline, local, my, reset, scalar, undef,
          wantarray

     Functions for processes and process groups
          alarm, exec, fork, getpgrp, getppid, getpriority, kill, pipe,
          qx/STRING/, setpgrp, setpriority, sleep, system, times, wait,
          waitpid

     Keywords related to perl modules
          do, import, no, package, require, use

     Keywords related to classes and object-orientedness
          bless, dbmclose, dbmopen, package, ref, tie, tied, untie, use

     Low-level socket functions
          accept, bind, connect, getpeername, getsockname, getsockopt, listen,
          recv, send, setsockopt, shutdown, socket, socketpair

     System V interprocess communication functions
          msgctl, msgget, msgrcv, msgsnd, semctl, semget, semop, shmctl,
          shmget, shmread, shmwrite

     Fetching user and group info
          endgrent, endhostent, endnetent, endpwent, getgrent, getgrgid,
          getgrnam, getlogin, getpwent, getpwnam, getpwuid, setgrent, setpwent

     Fetching network info
          endprotoent, endservent, gethostbyaddr, gethostbyname, gethostent,
          getnetbyaddr, getnetbyname, getnetent, getprotobyname,
          getprotobynumber, getprotoent, getservbyname, getservbyport,
          getservent, sethostent, setnetent, setprotoent, setservent

     Time-related functions
          gmtime, localtime, time, times

     Functions new in perl5
          abs, bless, chomp, chr, exists, formline, glob, import, lc, lcfirst,
          map, my, no, prototype, qx, qw, readline, readpipe, ref, sub*,
          sysopen, tie, tied, uc, ucfirst, untie, use

          * - sub was a keyword in perl4, but in perl5 it is an operator which
          can be used in expressions.





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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



     Functions obsoleted in perl5
          dbmclose, dbmopen

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     -X FILEHANDLE

     -X EXPR

     -X      A file test, where X is one of the letters listed below.  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.  Unless otherwise documented, it returns 1
             for TRUE and '' for FALSE, or the undefined value if the file
             doesn't exist.  Despite the funny names, precedence is the same
             as any other named unary operator, and the argument may be
             parenthesized like any other unary operator.  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 nonzero 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.
                 -t  Filehandle is opened to a tty.

                 -u  File has setuid bit set.
                 -g  File has setgid bit set.
                 -k  File has sticky bit set.

                 -T  File is a text file.
                 -B  File is a binary file (opposite of -T).






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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



                 -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 _s_t_a_t() 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 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 characters with the high bit set.  If too many odd
             characters (>30%) 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.  Because you have to read a file to do the
             -T test, on most occasions you want to use a -f against the file
             first, as in next unless -f $file && -T $file.

             If any of the file tests (or either the _s_t_a_t() or _l_s_t_a_t()
             operators) 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 _l_s_t_a_t() 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 _;








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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



                 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 _;


     abs VALUE

     abs     Returns the absolute value of its argument.  If VALUE is omitted,
             uses $_.

     accept NEWSOCKET,GENERICSOCKET
             Accepts an incoming socket connect, just as the _a_c_c_e_p_t(2) system
             call does.  Returns the packed address if it succeeded, FALSE
             otherwise.  See example in the section on _S_o_c_k_e_t_s: _C_l_i_e_n_t/_S_e_r_v_e_r
             _C_o_m_m_u_n_i_c_a_t_i_o_n in the _p_e_r_l_i_p_c manpage.

     alarm SECONDS

     alarm   Arranges to have a SIGALRM delivered to this process after the
             specified number of seconds have elapsed.  If SECONDS is not
             specified, the value stored in $_ is used. (On some machines,
             unfortunately, the elapsed time may be up to one second less than
             you specified because of how seconds are counted.)  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.

             For delays of finer granularity than one second, you may use
             Perl's _s_y_s_c_a_l_l() interface to access _s_e_t_i_t_i_m_e_r(2) if your system
             supports it, or else see the select() entry elsewhere in this
             document .  It is usually a mistake to intermix _a_l_a_r_m() and
             _s_l_e_e_p() calls.

             If you want to use _a_l_a_r_m() to time out a system call you need to
             use an eval/die pair.  You can't rely on the alarm causing the
             system call to fail with $! set to EINTR because Perl sets up
             signal handlers to restart system calls on some systems.  Using
             eval/die always works.










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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



                 eval {
                     local $SIG{ALRM} = sub { die "alarm\n" };       # NB \n required
                     alarm $timeout;
                     $nread = sysread SOCKET, $buffer, $size;
                     alarm 0;
                 };
                 die if $@ && $@ ne "alarm\n";       # propagate errors
                 if ($@) {
                     # timed out
                 }
                 else {
                     # didn't
                 }


     atan2 Y,X
             Returns the arctangent of Y/X in the range -pi to pi.

             For the tangent operation, you may use the _P_O_S_I_X::_t_a_n() function,
             or use the familiar relation:

                 sub tan { sin($_[0]) / cos($_[0])  }


     bind SOCKET,NAME
             Binds a network address to a socket, just as the bind system call
             does.  Returns TRUE if it succeeded, FALSE otherwise.  NAME
             should be a packed address of the appropriate type for the
             socket.  See the examples in the section on _S_o_c_k_e_t_s:
             _C_l_i_e_n_t/_S_e_r_v_e_r _C_o_m_m_u_n_i_c_a_t_i_o_n in the _p_e_r_l_i_p_c manpage.

     binmode FILEHANDLE
             Arranges for the file to be read or written in "binary" mode in
             operating systems that distinguish between binary and text files.
             Files that are not 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; in MS-DOS and similarly archaic systems, it
             may be imperative--otherwise your MS-DOS-damaged C library may
             mangle your file.  The key distinction between systems that need
             binmode and those that don't is their text file formats.  Systems
             like Unix and Plan9 that delimit lines with a single character,
             and that encode that character in C as '\n', do not need binmode.
             The rest need it.  If FILEHANDLE is an expression, the value is
             taken as the name of the filehandle.

     bless REF,CLASSNAME

     bless REF
             This function tells the thingy referenced by REF that it is now
             an object in the CLASSNAME package--or the current package if no
             CLASSNAME is specified, which is often the case.  It returns the
             reference for convenience, because a _b_l_e_s_s() is often the last



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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



             thing in a constructor.  Always use the two-argument version if
             the function doing the blessing might be inherited by a derived
             class.  See the _p_e_r_l_o_b_j manpage for more about the blessing (and
             blessings) of objects.

     caller EXPR

     caller  Returns the context of the current subroutine call.  In a scalar
             context, returns the caller's package name if there is a caller,
             that is, if we're in a subroutine or _e_v_a_l() or _r_e_q_u_i_r_e(), and the
             undefined value otherwise.  In a list context, returns

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

             With EXPR, it 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.

                 ($package, $filename, $line, $subroutine,
                  $hasargs, $wantarray, $evaltext, $is_require) = caller($i);

             Here $subroutine may be "(eval)" if the frame is not a subroutine
             call, but an eval.  In such a case additional elements $evaltext
             and $is_require are set: $is_require is true if the frame is
             created by a require or use statement, $evaltext contains the
             text of the eval EXPR statement.  In particular, for a eval BLOCK
             statement, $filename is "(eval)", but $evaltext is undefined.
             (Note also that each use statement creates a require frame inside
             an eval EXPR) frame.

             Furthermore, when called from within the DB package, caller
             returns more detailed information: it sets the list variable
             @DB::args to be the arguments with which the subroutine was
             invoked.

     chdir EXPR
             Changes the working directory to EXPR, if possible.  If EXPR is
             omitted, changes to home directory.  Returns TRUE upon success,
             FALSE otherwise.  See example under _d_i_e().

     chmod LIST
             Changes the permissions of a list of files.  The first element of
             the list must be the numerical mode, which should probably be an
             octal number, and which definitely should _n_o_t a string of octal
             digits:  0644 is okay, '0644' is not.  Returns the number of
             files successfully changed.  See also the oct entry elsewhere in
             this document if all you have is a string.








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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



                 $cnt = chmod 0755, 'foo', 'bar';
                 chmod 0755, @executables;
                 $mode = '0644'; chmod $mode, 'foo';      # !!! sets mode to --w----r-T
                 $mode = '0644'; chmod oct($mode), 'foo'; # this is better
                 $mode = 0644;   chmod $mode, 'foo';      # this is best


     chomp VARIABLE

     chomp LIST

     chomp   This is a slightly safer version of the chop entry elsewhere in
             this document .  It removes any line ending that corresponds to
             the current value of $/ (also known as $INPUT_RECORD_SEPARATOR in
             the English module).  It returns the total number of characters
             removed from all its arguments.  It's often used to remove the
             newline from the end of an input record when you're worried that
             the final record may be missing its newline.  When in paragraph
             mode ($/ = ""), it removes all trailing newlines from the string.
             If VARIABLE is omitted, it chomps $_.  Example:

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

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

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

             If you chomp a list, each element is chomped, and the total
             number of characters removed is returned.

     chop VARIABLE

     chop LIST

     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(/:/);
                     ...
                 }




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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



             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.

             Note that chop returns the last character.  To return all but the
             last character, use substr($string, 0, -1).

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

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

             Here's an example that looks up nonnumeric uids in the passwd
             file:

                 print "User: ";
                 chop($user = <STDIN>);
                 print "Files: "
                 chop($pattern = <STDIN>);

                 ($login,$pass,$uid,$gid) = getpwnam($user)
                     or die "$user not in passwd file";

                 @ary = <${pattern}>;        # expand filenames
                 chown $uid, $gid, @ary;

             On most systems, you are not allowed to change the ownership of
             the file unless you're the superuser, although you should be able
             to change the group to any of your secondary groups.  On insecure
             systems, these restrictions may be relaxed, but this is not a
             portable assumption.

     chr NUMBER

     chr     Returns the character represented by that NUMBER in the character
             set.  For example, chr(65) is "A" in ASCII.  For the reverse, use
             the ord entry elsewhere in this document .

             If NUMBER is omitted, uses $_.

     chroot FILENAME






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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



     chroot  This function works as the system call by the same name: it makes
             the named directory the new root directory for all further
             pathnames that begin with a "/" by your process and all of its
             children.  (It doesn't change your current working directory,
             which is unaffected.)  For security reasons, this call is
             restricted to the superuser.  If FILENAME is omitted, does chroot
             to $_.

     close FILEHANDLE
             Closes the file or pipe associated with the file handle,
             returning TRUE only if stdio successfully flushes buffers and
             closes the system file descriptor.

             You don't have to close FILEHANDLE if you are immediately going
             to do another _o_p_e_n() on it, because _o_p_e_n() will close it for you.
             (See _o_p_e_n().)  However, an explicit close on an input file resets
             the line counter ($.), while the implicit close done by _o_p_e_n()
             does not.

             If the file handle came from a piped open close will additionally
             return FALSE if one of the other system calls involved fails or
             if the program exits with non-zero status.  (If the only problem
             was that the program exited non-zero $! will be set to 0.) 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 exit status
             value of the command into $?.  Example:

                 open(OUTPUT, '|sort >foo')  # pipe to sort
                     or die "Can't start sort: $!";
                 ...                         # print stuff to output
                 close OUTPUT                # wait for sort to finish
                     or warn $! ? "Error closing sort pipe: $!"
                                : "Exit status $? from sort";
                 open(INPUT, 'foo')          # get sort's results
                     or die "Can't open 'foo' for input: $!";

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

     closedir DIRHANDLE
             Closes a directory opened by _o_p_e_n_d_i_r().

     connect SOCKET,NAME
             Attempts to connect to a remote socket, just as the connect
             system call does.  Returns TRUE if it succeeded, FALSE otherwise.
             NAME should be a packed address of the appropriate type for the
             socket.  See the examples in the section on _S_o_c_k_e_t_s:
             _C_l_i_e_n_t/_S_e_r_v_e_r _C_o_m_m_u_n_i_c_a_t_i_o_n in the _p_e_r_l_i_p_c manpage.






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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



     continue BLOCK
             Actually a flow control statement rather than a function.  If
             there is a continue BLOCK attached to a BLOCK (typically in a
             while or foreach), it is always executed just before the
             conditional is about to be evaluated again, just like 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 (which is similar to the C continue statement).

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

             For the inverse cosine operation, you may use the _P_O_S_I_X::_a_c_o_s()
             function, or use this relation:

                 sub acos { atan2( sqrt(1 - $_[0] * $_[0]), $_[0] ) }


     crypt PLAINTEXT,SALT
             Encrypts a string exactly like the _c_r_y_p_t(3) function in the C
             library (assuming that you actually have a version there that has
             not been extirpated as a potential munition).  This can prove
             useful for checking the password file for lousy passwords,
             amongst other things.  Only the guys wearing white hats should do
             this.

             Note that crypt is intended to be a one-way function, much like
             breaking eggs to make an omelette.  There is no (known)
             corresponding decrypt function.  As a result, this function isn't
             all that useful for cryptography.  (For that, see your nearby
             CPAN mirror.)

             Here's an example that makes sure that whoever runs this program
             knows their own password:

                 $pwd = (getpwuid($<))[1];
                 $salt = substr($pwd, 0, 2);

                 system "stty -echo";
                 print "Password: ";
                 chop($word = <STDIN>);
                 print "\n";
                 system "stty echo";

                 if (crypt($word, $salt) ne $pwd) {
                     die "Sorry...\n";
                 } else {
                     print "ok\n";
                 }

             Of course, typing in your own password to whoever asks you for it



                                                                       PPPPaaaaggggeeee 11112222






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



             is unwise.

     dbmclose HASH
             [This function has been superseded by the _u_n_t_i_e() function.]

             Breaks the binding between a DBM file and a hash.

     dbmopen HASH,DBNAME,MODE
             [This function has been superseded by the _t_i_e() function.]

             This binds a _d_b_m(3), _n_d_b_m(3), _s_d_b_m(3), _g_d_b_m(), or Berkeley DB
             file to a hash.  HASH is the name of the hash.  (Unlike normal
             open, the first argument is _N_O_T a filehandle, even though it
             looks like one).  DBNAME is the name of the database (without the
             ._d_i_r or ._p_a_g extension if any).  If the database does not exist,
             it is created with protection specified by MODE (as modified by
             the _u_m_a_s_k()).  If your system supports only the older DBM
             functions, you may perform only one _d_b_m_o_p_e_n() in your program.
             In older versions of Perl, if your system had neither DBM nor
             ndbm, calling _d_b_m_o_p_e_n() produced a fatal error; it now falls back
             to _s_d_b_m(3).

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

             Note that functions such as _k_e_y_s() and _v_a_l_u_e_s() may return huge
             array values when used on large DBM files.  You may prefer to use
             the _e_a_c_h() 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);

             See also the _A_n_y_D_B_M__F_i_l_e manpage for a more general description
             of the pros and cons of the various dbm approaches, as well as
             the _D_B__F_i_l_e manpage for a particularly rich implementation.

     defined EXPR

     defined Returns a Boolean value telling whether EXPR has a value other
             than the undefined value undef.  If EXPR is not present, $_ will
             be checked.

             Many operations return undef to indicate failure, end of file,
             system error, uninitialized variable, and other exceptional
             conditions.  This function allows you to distinguish undef from
             other values.  (A simple Boolean test will not distinguish among



                                                                       PPPPaaaaggggeeee 11113333






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



             undef, zero, the empty string, and "0", which are all equally
             false.)  Note that since undef is a valid scalar, its presence
             doesn't _n_e_c_e_s_s_a_r_i_l_y indicate an exceptional condition: _p_o_p()
             returns undef when its argument is an empty array, _o_r when the
             element to return happens to be undef.

             You may also use _d_e_f_i_n_e_d() to check whether a subroutine exists.
             On the other hand, use of _d_e_f_i_n_e_d() upon aggregates (hashes and
             arrays) is not guaranteed to produce intuitive results, and
             should probably be avoided.

             When used on a hash element, it tells you whether the value is
             defined, not whether the key exists in the hash.  Use the exists
             entry elsewhere in this document for the latter purpose.

             Examples:

                 print if defined $switch{'D'};
                 print "$val\n" while defined($val = pop(@ary));
                 die "Can't readlink $sym: $!"
                     unless defined($value = readlink $sym);
                 sub foo { defined &$bar ? &$bar(@_) : die "No bar"; }
                 $debugging = 0 unless defined $debugging;

             Note:  Many folks tend to overuse _d_e_f_i_n_e_d(), and then are
             surprised to discover that the number 0 and "" (the zero-length
             string) are, in fact, defined values.  For example, if you say

                 "ab" =~ /a(.*)b/;

             the pattern match succeeds, and $1 is defined, despite the fact
             that it matched "nothing".  But it didn't really match nothing--
             rather, it matched something that happened to be 0 characters
             long.  This is all very above-board and honest.  When a function
             returns an undefined value, it's an admission that it couldn't
             give you an honest answer.  So you should use _d_e_f_i_n_e_d() only when
             you're questioning the integrity of what you're trying to do.  At
             other times, a simple comparison to 0 or "" is what you want.

             Currently, using _d_e_f_i_n_e_d() on an entire array or hash reports
             whether memory for that aggregate has ever been allocated.  So an
             array you set to the empty list appears undefined initially, and
             one that once was full and that you then set to the empty list
             still appears defined.  You should instead use a simple test for
             size:

                 if (@an_array) { print "has array elements\n" }
                 if (%a_hash)   { print "has hash members\n"   }

             Using _u_n_d_e_f() on these, however, does clear their memory and then
             report them as not defined anymore, but you shoudln't do that
             unless you don't plan to use them again, because it saves time



                                                                       PPPPaaaaggggeeee 11114444






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



             when you load them up again to have memory already ready to be
             filled.

             This counterintuitive behaviour of _d_e_f_i_n_e_d() on aggregates may be
             changed, fixed, or broken in a future release of Perl.

             See also the undef, exists,  and ref entries elsewhere in this
             document .

     delete EXPR
             Deletes the specified _k_e_y(s) and their associated values from a
             hash.  For each key, returns the deleted value associated with
             that key, or the undefined value if there was no such key.
             Deleting from $ENV{} modifies the environment.  Deleting from a
             hash tied to a DBM file deletes the entry from the DBM file.
             (But deleting from a _t_i_e()d hash doesn't necessarily return
             anything.)

             The following deletes all the values of a hash:

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

             And so does this:

                 delete @HASH{keys %HASH}

             (But both of these are slower than the _u_n_d_e_f() command.)  Note
             that the EXPR can be arbitrarily complicated as long as the final
             operation is a hash element lookup or hash slice:

                 delete $ref->[$x][$y]{$key};
                 delete @{$ref->[$x][$y]}{$key1, $key2, @morekeys};


     die LIST
             Outside of an _e_v_a_l(), prints the value of LIST to STDERR and
             exits with the current value of $! (errno).  If $! is 0, exits
             with the value of ($? >> 8) (backtick `command` status).  If ($?
             >> 8) is 0, exits with 255.  Inside an _e_v_a_l(), the error message
             is stuffed into $@, and the _e_v_a_l() is terminated with the
             undefined value; this makes _d_i_e() the way to raise an exception.

             Equivalent examples:

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



                                                                       PPPPaaaaggggeeee 11115555






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



             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.

             See also _e_x_i_t() and _w_a_r_n().

             If LIST is empty and $@ already contains a value (typically from
             a previous eval) that value is reused after appending
             "\t...propagated".  This is useful for propagating exceptions:

                 eval { ... };
                 die unless $@ =~ /Expected exception/;

             If $@ is empty then the string "Died" is used.

             You can arrange for a callback to be called just before the _d_i_e()
             does its deed, by setting the $SIG{__DIE__} hook.  The associated
             handler will be called with the error text and can change the
             error message, if it sees fit, by calling _d_i_e() again.  See the
             section on $_S_I_G{_e_x_p_r} in the _p_e_r_l_v_a_r manpage for details on
             setting %SIG entries, and the section on _e_v_a_l _B_L_O_C_K for some
             examples.

             Note that the $SIG{__DIE__} hook is called even inside _e_v_a_l()ed
             blocks/strings.  If one wants the hook to do nothing in such
             situations, put

                     die @_ if $^S;

             as the first line of the handler (see the section on $^_S in the
             _p_e_r_l_v_a_r manpage).

     do BLOCK
             Not really a function.  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)
             A deprecated form of subroutine call.  See the _p_e_r_l_s_u_b manpage.






                                                                       PPPPaaaaggggeeee 11116666






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



     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

                 scalar 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 the section on _P_r_e_d_e_f_i_n_e_d _N_a_m_e_s in the _p_e_r_l_v_a_r
             manpage).  It's the same, however, in that it does reparse the
             file every time you call it, so you probably don't want to do
             this inside a loop.

             Note that inclusion of library modules is better done with the
             _u_s_e() and _r_e_q_u_i_r_e() operators, which also do error checking and
             raise an exception if there's a problem.

     dump LABEL
             This causes an immediate core dump.  Primarily this is so that
             you can use the uuuunnnndddduuuummmmpppp 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 ----uuuu option in the _p_e_r_l_r_u_n manpage.

             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';




                                                                       PPPPaaaaggggeeee 11117777






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



                 QUICKSTART:
                 Getopt('f');


     each HASH
             When called in a list context, returns a 2-element array
             consisting of the key and value for the next element of a hash,
             so that you can iterate over it.  When called in a scalar
             context, returns the key for only the next element in the hash.
             (Note: Keys may be "0" or "", which are logically false; you may
             wish to avoid constructs like while ($k = each %foo) {} for this
             reason.)

             Entries are returned in an apparently random order.  When the
             hash is entirely read, a null array is returned in list context
             (which when assigned produces a FALSE (0) value), and undef is
             returned in a scalar context.  The next call to _e_a_c_h() after that
             will start iterating again.  There is a single iterator for each
             hash, shared by all _e_a_c_h(), _k_e_y_s(), and _v_a_l_u_e_s() function calls
             in the program; it can be reset by reading all the elements from
             the hash, or by evaluating keys HASH or values HASH.  If you add
             or delete elements of a hash while you're iterating over it, you
             may get entries skipped or duplicated, so don't.

             The following prints out your environment like the _p_r_i_n_t_e_n_v(1)
             program, only in a different order:

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

             See also _k_e_y_s() and _v_a_l_u_e_s().

     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 _u_n_g_e_t_c()s it, so it
             is not very useful in an interactive context.)  Do not read from
             a terminal file (or call eof(FILEHANDLE) on it) after end-of-file
             is reached.  Filetypes such as terminals may lose the end-of-file
             condition if you do.

             An eof without an argument uses the last file read as argument.
             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 _E_A_C_H file in a while (<>) loop.  Examples:



                                                                       PPPPaaaaggggeeee 11118888






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



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

                 # insert dashes just before last line of last file
                 while (<>) {
                     if (eof()) {
                         print "--------------\n";
                         close(ARGV);        # close or break; is needed if we
                                             # are reading from the terminal
                     }
                     print;
                 }

             Practical hint: you almost never need to use eof in Perl, because
             the input operators return undef when they run out of data.

     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 or subroutine and format definitions
             remain afterwards.  The value returned is the value of the last
             expression evaluated, or a return statement may be used, just as
             with subroutines.  The last expression is evaluated in scalar or
             array context, depending on the context of the eval.

             If there is a syntax error or runtime error, or a _d_i_e() statement
             is executed, an undefined value is returned by _e_v_a_l(), 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.  Beware that using _e_v_a_l() neither silences perl from
             printing warnings to STDERR, nor does it stuff the text of
             warning messages into $@.  To do either of those, you have to use
             the $SIG{__WARN__} facility.  See _w_a_r_n() and the _p_e_r_l_v_a_r manpage.

             Note that, because _e_v_a_l() traps otherwise-fatal errors, it is
             useful for determining whether a particular feature (such as
             _s_o_c_k_e_t() or _s_y_m_l_i_n_k()) 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 $@.  Examples:





                                                                       PPPPaaaaggggeeee 11119999






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



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

                 # same thing, but less efficient
                 eval '$answer = $a / $b'; warn $@ if $@;

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

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

             When using the eval{} form as an exception trap in libraries, you
             may wish not to trigger any __DIE__ hooks that user code may have
             installed.  You can use the local $SIG{__DIE__} construct for
             this purpose, as shown in this example:

                 # a very private exception trap for divide-by-zero
                 eval { local $SIG{'__DIE__'}; $answer = $a / $b; }; warn $@ if $@;

             This is especially significant, given that __DIE__ hooks can call
             _d_i_e() again, which has the effect of changing their error
             messages:

                 # __DIE__ hooks may modify error messages
                 {
                    local $SIG{'__DIE__'} = sub { (my $x = $_[0]) =~ s/foo/bar/g; die $x };
                    eval { die "foo foofs here" };
                    print $@ if $@;                # prints "bar barfs here"
                 }

             With an _e_v_a_l(), you should be especially careful to remember
             what's being looked at when:

                 eval $x;            # CASE 1
                 eval "$x";          # CASE 2

                 eval '$x';          # CASE 3
                 eval { $x };        # CASE 4

                 eval "\$$x++"       # CASE 5
                 $$x++;              # CASE 6

             Cases 1 and 2 above behave identically: they run the code
             contained in the variable $x.  (Although case 2 has misleading
             double quotes making the reader wonder what else might be
             happening (nothing is).)  Cases 3 and 4 likewise behave in the
             same way: they run the code '$x', which does nothing but return
             the value of $x.  (Case 4 is preferred for purely visual reasons,
             but it also has the advantage of compiling at compile-time
             instead of at run-time.)  Case 5 is a place where normally you
             _W_O_U_L_D like to use double quotes, except that in this particular



                                                                       PPPPaaaaggggeeee 22220000






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



             situation, you can just use symbolic references instead, as in
             case 6.

     exec LIST
             The _e_x_e_c() function executes a system command _A_N_D _N_E_V_E_R _R_E_T_U_R_N_S -
             use _s_y_s_t_e_m() instead of _e_x_e_c() if you want it to return. It fails
             and returns FALSE only if the command does not exist _a_n_d it is
             executed directly instead of via your system's command shell (see
             below).

             If there is more than one argument in LIST, or if LIST is an
             array with more than one value, calls _e_x_e_c_v_p(3) with the
             arguments in LIST.  If there is only one scalar argument, the
             argument is checked for shell metacharacters, and if there are
             any, the entire argument is passed to the system's command shell
             for parsing (this is /bin/sh -c on Unix platforms, but varies on
             other platforms).  If there are no shell metacharacters in the
             argument, it is split into words and passed directly to _e_x_e_c_v_p(),
             which is more efficient.  Note: _e_x_e_c() and _s_y_s_t_e_m() 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 as an "indirect
             object" (without a comma) in front of the LIST.  (This always
             forces interpretation of the LIST as a multivalued 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

             or, more directly,

                 exec {'/bin/csh'} '-sh';    # pretend it's a login shell

             When the arguments get executed via the system shell, results
             will be subject to its quirks and capabilities.  See the section
             on `_S_T_R_I_N_G` in the _p_e_r_l_o_p manpage for details.

     exists EXPR
             Returns TRUE if the specified hash key exists in its hash array,
             even if the corresponding value is undefined.

                 print "Exists\n" if exists $array{$key};
                 print "Defined\n" if defined $array{$key};
                 print "True\n" if $array{$key};

             A hash element can be TRUE only if it's defined, and defined if



                                                                       PPPPaaaaggggeeee 22221111






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



             it exists, but the reverse doesn't necessarily hold true.

             Note that the EXPR can be arbitrarily complicated as long as the
             final operation is a hash key lookup:

                 if (exists $ref->[$x][$y]{$key}) { ... }


     exit EXPR
             Evaluates EXPR and exits immediately with that value.  (Actually,
             it calls any defined END routines first, but the END routines may
             not abort the exit.  Likewise any object destructors that need to
             be called are called before exit.)  Example:

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

             See also _d_i_e().  If EXPR is omitted, exits with 0 status.  The
             only universally portable values for EXPR are 0 for success and 1
             for error; all other values are subject to unpredictable
             interpretation depending on the environment in which the Perl
             program is running.

             You shouldn't use _e_x_i_t() to abort a subroutine if there's any
             chance that someone might want to trap whatever error happened.
             Use _d_i_e() instead, which can be trapped by an _e_v_a_l().

     exp EXPR

     exp     Returns _e (the natural logarithm base) to the power of EXPR.  If
             EXPR is omitted, gives exp($_).

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

                 use Fcntl;

             first to get the correct function definitions.  Argument
             processing and value return works just like _i_o_c_t_l() below.  Note
             that _f_c_n_t_l() will produce a fatal error if used on a machine that
             doesn't implement _f_c_n_t_l(2).  For example:

                 use Fcntl;
                 fcntl($filehandle, F_GETLK, $packed_return_buffer);


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





                                                                       PPPPaaaaggggeeee 22222222






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



     flock FILEHANDLE,OPERATION
             Calls _f_l_o_c_k(2), or an emulation of it, on FILEHANDLE.  Returns
             TRUE for success, FALSE on failure.  Produces a fatal error if
             used on a machine that doesn't implement _f_l_o_c_k(2), _f_c_n_t_l(2)
             locking, or _l_o_c_k_f(3).  _f_l_o_c_k() is Perl's portable file locking
             interface, although it locks only entire files, not records.

             OPERATION is one of LOCK_SH, LOCK_EX, or LOCK_UN, possibly
             combined with LOCK_NB.  These constants are traditionally valued
             1, 2, 8 and 4, but you can use the symbolic names if import them
             from the Fcntl module, either individually, or as a group using
             the ':flock' tag.  LOCK_SH requests a shared lock, LOCK_EX
             requests an exclusive lock, and LOCK_UN releases a previously
             requested lock.  If LOCK_NB is added to LOCK_SH or LOCK_EX then
             _f_l_o_c_k() will return immediately rather than blocking waiting for
             the lock (check the return status to see if you got it).

             To avoid the possibility of mis-coordination, Perl flushes
             FILEHANDLE before (un)locking it.

             Note that the emulation built with _l_o_c_k_f(3) doesn't provide
             shared locks, and it requires that FILEHANDLE be open with write
             intent.  These are the semantics that _l_o_c_k_f(3) implements.  Most
             (all?) systems implement _l_o_c_k_f(3) in terms of _f_c_n_t_l(2) locking,
             though, so the differing semantics shouldn't bite too many
             people.

             Note also that some versions of _f_l_o_c_k() cannot lock things over
             the network; you would need to use the more system-specific
             _f_c_n_t_l() for that.  If you like you can force Perl to ignore your
             system's _f_l_o_c_k(2) function, and so provide its own _f_c_n_t_l(2)-based
             emulation, by passing the switch -Ud_flock to the _C_o_n_f_i_g_u_r_e
             program when you configure perl.

             Here's a mailbox appender for BSD systems.

                 use Fcntl ':flock'; # import LOCK_* constants

                 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'}")
                         or die "Can't open mailbox: $!";




                                                                       PPPPaaaaggggeeee 22223333






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



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

             See also the _D_B__F_i_l_e manpage for other _f_l_o_c_k() examples.

     fork    Does a _f_o_r_k(2) system call.  Returns the child pid to the parent
             process and 0 to the child process, or undef if the fork is
             unsuccessful.  Note: unflushed buffers remain unflushed in both
             processes, which means you may need to set $| ($AUTOFLUSH in
             English) or call the _a_u_t_o_f_l_u_s_h() method of IO::Handle to avoid
             duplicate output.

             If you _f_o_r_k() without ever waiting on your children, you will
             accumulate zombies:

                 $SIG{CHLD} = sub { wait };

             There's also the double-fork trick (error checking on _f_o_r_k()
             returns omitted);

                 unless ($pid = fork) {
                     unless (fork) {
                         exec "what you really wanna do";
                         die "no exec";
                         # ... or ...
                         ## (some_perl_code_here)
                         exit 0;
                     }
                     exit 0;
                 }
                 waitpid($pid,0);

             See also the _p_e_r_l_i_p_c manpage for more examples of forking and
             reaping moribund children.

             Note that if your forked child inherits system file descriptors
             like STDIN and STDOUT that are actually connected by a pipe or
             socket, even if you exit, the remote server (such as, say, httpd
             or rsh) won't think you're done.  You should reopen those to
             /dev/null if it's any issue.

     format  Declare a picture format with use by the _w_r_i_t_e() function.  For
             example:

                 format Something =
                     Test: @<<<<<<<< @||||| @>>>>>
                           $str,     $%,    '$' . int($num)
                 .






                                                                       PPPPaaaaggggeeee 22224444






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



                 $str = "widget";
                 $num = $cost/$quantity;
                 $~ = 'Something';
                 write;

             See the _p_e_r_l_f_o_r_m manpage for many details and examples.

     formline PICTURE,LIST
             This is an internal function used by formats, though you may call
             it too.  It formats (see the _p_e_r_l_f_o_r_m manpage) a list of values
             according to the contents of PICTURE, placing the output into the
             format output accumulator, $^A (or $ACCUMULATOR in English).
             Eventually, when a _w_r_i_t_e() is done, the contents of $^A are
             written to some filehandle, but you could also read $^A yourself
             and then set $^A back to "".  Note that a format typically does
             one _f_o_r_m_l_i_n_e() per line of form, but the _f_o_r_m_l_i_n_e() function
             itself doesn't care how many newlines are embedded in the
             PICTURE.  This means that the ~ and ~~ tokens will treat the
             entire PICTURE as a single line.  You may therefore need to use
             multiple formlines to implement a single record format, just like
             the format compiler.

             Be careful if you put double quotes around the picture, because
             an "@" character may be taken to mean the beginning of an array
             name.  _f_o_r_m_l_i_n_e() always returns TRUE.  See the _p_e_r_l_f_o_r_m manpage
             for other examples.

     getc FILEHANDLE

     getc    Returns the next character from the input file attached to
             FILEHANDLE, or a null string at end of file.  If FILEHANDLE is
             omitted, reads from STDIN.  This is not particularly efficient.
             It cannot be used to get unbuffered single-characters, however.
             For that, try something more like:

                 if ($BSD_STYLE) {
                     system "stty cbreak </dev/tty >/dev/tty 2>&1";
                 }
                 else {
                     system "stty", '-icanon', 'eol', "\001";
                 }

                 $key = getc(STDIN);

                 if ($BSD_STYLE) {
                     system "stty -cbreak </dev/tty >/dev/tty 2>&1";
                 }
                 else {
                     system "stty", 'icanon', 'eol', '^@'; # ASCII null
                 }
                 print "\n";




                                                                       PPPPaaaaggggeeee 22225555






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



             Determination of whether $BSD_STYLE should be set is left as an
             exercise to the reader.

             The _P_O_S_I_X::_g_e_t_a_t_t_r() function can do this more portably on
             systems alleging POSIX compliance.  See also the Term::ReadKey
             module from your nearest CPAN site; details on CPAN can be found
             on the CPAN entry in the _p_e_r_l_m_o_d manpage.

     getlogin
             Returns the current login from /_e_t_c/_u_t_m_p, if any.  If null, use
             _g_e_t_p_w_u_i_d().

                 $login = getlogin || getpwuid($<) || "Kilroy";

             Do not consider _g_e_t_l_o_g_i_n() for authentication: it is not as
             secure as _g_e_t_p_w_u_i_d().

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

                 use Socket;
                 $hersockaddr    = getpeername(SOCK);
                 ($port, $iaddr) = unpack_sockaddr_in($hersockaddr);
                 $herhostname    = gethostbyaddr($iaddr, AF_INET);
                 $herstraddr     = inet_ntoa($iaddr);


     getpgrp PID
             Returns the current process group for the specified PID.  Use a
             PID of 0 to get the current process group for the current
             process.  Will raise an exception if used on a machine that
             doesn't implement _g_e_t_p_g_r_p(2).  If PID is omitted, returns process
             group of current process.  Note that the POSIX version of
             _g_e_t_p_g_r_p() does not accept a PID argument, so only PID==0 is truly
             portable.

     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 the _g_e_t_p_r_i_o_r_i_t_y(_2) manpage.)  Will raise a fatal
             exception if used on a machine that doesn't implement
             _g_e_t_p_r_i_o_r_i_t_y(2).

     getpwnam NAME

     getgrnam NAME

     gethostbyname NAME





                                                                       PPPPaaaaggggeeee 22226666






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



     getnetbyname NAME

     getprotobyname NAME

     getpwuid UID

     getgrgid GID

     getservbyname NAME,PROTO

     gethostbyaddr ADDR,ADDRTYPE

     getnetbyaddr ADDR,ADDRTYPE

     getprotobynumber NUMBER

     getservbyport PORT,PROTO

     getpwent

     getgrent

     gethostent

     getnetent

     getprotoent

     getservent

     setpwent

     setgrent

     sethostent STAYOPEN

     setnetent STAYOPEN

     setprotoent STAYOPEN

     setservent STAYOPEN

     endpwent

     endgrent

     endhostent

     endnetent






                                                                       PPPPaaaaggggeeee 22227777






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



     endprotoent

     endservent
             These routines perform the same functions as their counterparts
             in the system library.  Within a list 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:

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

             The $members value returned by _g_e_t_g_r*() is a space separated list
             of the login names of the members of the group.

             For the _g_e_t_h_o_s_t*() 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.

                 use Socket;
                 $mysockaddr = getsockname(SOCK);
                 ($port, $myaddr) = unpack_sockaddr_in($mysockaddr);





                                                                       PPPPaaaaggggeeee 22228888






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



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

     glob EXPR

     glob    Returns the value of EXPR with filename expansions such as a
             shell would do.  This is the internal function implementing the
             <*.c> operator, but you can use it directly.  If EXPR is omitted,
             $_ is used.  The <*.c> operator is discussed in more detail in
             the section on _I/_O _O_p_e_r_a_t_o_r_s in the _p_e_r_l_o_p manpage.

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

                 #  0    1    2     3     4    5     6     7     8
                 ($sec,$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 0..6 with sunday as day 0.  Also, $year is
             the number of years since 1900, _n_o_t simply the last two digits of
             the year.

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

             In a scalar context, returns the _c_t_i_m_e(3) value:

                 $now_string = gmtime;  # e.g., "Thu Oct 13 04:54:34 1994"

             Also see the _t_i_m_e_g_m() function provided by the Time::Local
             module, and the _s_t_r_f_t_i_m_e(3) function available via the POSIX
             module.

     goto LABEL

     goto EXPR

     goto &NAME
             The goto-LABEL form finds the statement labeled with LABEL and
             resumes execution there.  It may not be used to go into any
             construct that requires initialization, such as a subroutine or a
             foreach loop.  It also can't be used to go into a construct that
             is optimized away, or to get out of a block or subroutine given
             to _s_o_r_t().  It can be used to go almost anywhere else within the
             dynamic scope, including out of subroutines, but it's usually
             better to use some other construct such as last or die.  The
             author of Perl has never felt the need to use this form of goto
             (in Perl, that is--C is another matter).



                                                                       PPPPaaaaggggeeee 22229999






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



             The goto-EXPR form expects a label name, whose scope will be
             resolved dynamically.  This allows for computed gotos per
             FORTRAN, but isn't necessarily recommended if you're optimizing
             for maintainability:

                 goto ("FOO", "BAR", "GLARCH")[$i];

             The goto-&NAME form is highly magical, and substitutes a call to
             the named subroutine for the currently running subroutine.  This
             is used by AUTOLOAD subroutines that wish to load another
             subroutine and then pretend that the other subroutine had been
             called in the first place (except that any modifications to @_ in
             the current subroutine are propagated to the other subroutine.)
             After the goto, not even _c_a_l_l_e_r() will be able to tell that this
             routine was called first.

     grep BLOCK LIST

     grep EXPR,LIST
             This is similar in spirit to, but not the same as, _g_r_e_p(1) and
             its relatives.  In particular, it is not limited to using regular
             expressions.

             Evaluates the BLOCK or EXPR for each element of LIST (locally
             setting $_ to each element) and returns the list 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

             or equivalently,

                 @foo = grep {!/^#/} @bar;    # weed out comments

             Note that, because $_ is a reference into the list 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.  Similarly, grep returns aliases into the
             original list, much like the way that the section on _F_o_r_e_a_c_h
             _L_o_o_p_s's index variable aliases the list elements.  That is,
             modifying an element of a list returned by grep (for example, in
             a foreach, map or another grep) actually modifies the element in
             the original list.

             See also the map entry elsewhere in this document for an array
             composed of the results of the BLOCK or EXPR.

     hex EXPR






                                                                       PPPPaaaaggggeeee 33330000






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



     hex     Interprets EXPR as a hex string and returns the corresponding
             value.  (To convert strings that might start with either 0 or 0x
             see the oct entry elsewhere in this document .)  If EXPR is
             omitted, uses $_.

                 print hex '0xAf'; # prints '175'
                 print hex 'aF';   # same


     import  There is no builtin _i_m_p_o_r_t() function.  It is merely an ordinary
             method (subroutine) defined (or inherited) by modules that wish
             to export names to another module.  The _u_s_e() function calls the
             _i_m_p_o_r_t() method for the package used.  See also the use() entry
             elsewhere in this document the _p_e_r_l_m_o_d manpage, and the _E_x_p_o_r_t_e_r
             manpage.

     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--but don't do that).  If
             the substring is not found, returns one less than the base,
             ordinarily -1.

     int EXPR

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

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

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

             first to get the correct function definitions.  If _i_o_c_t_l._p_h
             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
             <_s_y_s/_i_o_c_t_l._h>.  (There is a Perl script called hhhh2222pppphhhh that comes
             with the Perl kit which may help you in this, but it's
             nontrivial.)  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
             _p_a_c_k() and _u_n_p_a_c_k() functions are useful for manipulating the
             values of structures used by _i_o_c_t_l().  The following example sets
             the erase character to DEL.





                                                                       PPPPaaaaggggeeee 33331111






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



                 require 'ioctl.ph';
                 $getp = &TIOCGETP;
                 die "NO TIOCGETP" if $@ || !$getp;
                 $sgttyb_t = "ccccs";                # 4 chars and a short
                 if (ioctl(STDIN,$getp,$sgttyb)) {
                     @ary = unpack($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:          then 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;


     join EXPR,LIST
             Joins the separate strings of LIST 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 the split entry in the _p_e_r_l_f_u_n_c manpage.

     keys HASH
             Returns a normal array consisting of all the keys of the named
             hash.  (In a scalar context, returns the number of keys.)  The
             keys are returned in an apparently random order, but it is the
             same order as either the _v_a_l_u_e_s() or _e_a_c_h() function produces
             (given that the hash has not been modified).  As a side effect,
             it resets HASH's iterator.

             Here is yet another way to print your environment:

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




                                                                       PPPPaaaaggggeeee 33332222






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



             or how about sorted by key:

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

             To sort an array by value, you'll need to use a sort function.
             Here's a descending numeric sort of a hash by its values:

                 foreach $key (sort { $hash{$b} <=> $hash{$a} } keys %hash)) {
                     printf "%4d %s\n", $hash{$key}, $key;
                 }

             As an lvalue keys allows you to increase the number of hash
             buckets allocated for the given hash.  This can gain you a
             measure of efficiency if you know the hash is going to get big.
             (This is similar to pre-extending an array by assigning a larger
             number to $#array.)  If you say

                 keys %hash = 200;

             then %hash will have at least 200 buckets allocated for it.
             These buckets will be retained even if you do %hash = (), use
             undef %hash if you want to free the storage while %hash is still
             in scope.  You can't shrink the number of buckets allocated for
             the hash using keys in this way (but you needn't worry about
             doing this by accident, as trying has no effect).

     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;

             Unlike in the shell, in Perl if the _S_I_G_N_A_L is negative, it kills
             process groups instead of processes.  (On System V, a negative
             _P_R_O_C_E_S_S number will also kill process groups, but that's not
             portable.)  That means you usually want to use positive not
             negative signals.  You may also use a signal name in quotes.  See
             the section on _S_i_g_n_a_l_s in the _p_e_r_l_i_p_c manpage for details.

     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:






                                                                       PPPPaaaaggggeeee 33333333






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



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


     lc EXPR

     lc      Returns an lowercased version of EXPR.  This is the internal
             function implementing the \L escape in double-quoted strings.
             Respects current LC_CTYPE locale if use locale in force.  See the
             _p_e_r_l_l_o_c_a_l_e manpage.

             If EXPR is omitted, uses $_.

     lcfirst EXPR

     lcfirst Returns the value of EXPR with the first character lowercased.
             This is the internal function implementing the \l escape in
             double-quoted strings.  Respects current LC_CTYPE locale if use
             locale in force.  See the _p_e_r_l_l_o_c_a_l_e manpage.

             If EXPR is omitted, uses $_.

     length EXPR

     length  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 the
             section on _S_o_c_k_e_t_s: _C_l_i_e_n_t/_S_e_r_v_e_r _C_o_m_m_u_n_i_c_a_t_i_o_n in the _p_e_r_l_i_p_c
             manpage.

     local EXPR
             A local modifies the listed variables to be local to the
             enclosing block, subroutine, eval{}, or do.  If more than one
             value is listed, the list must be placed in parentheses.  See the
             section on _T_e_m_p_o_r_a_r_y _V_a_l_u_e_s _v_i_a _l_o_c_a_l() in the _p_e_r_l_s_u_b manpage
             for details, including issues with tied arrays and hashes.

             But you really probably want to be using _m_y() instead, because
             _l_o_c_a_l() isn't what most people think of as "local").  See the
             section on _P_r_i_v_a_t_e _V_a_r_i_a_b_l_e_s _v_i_a _m_y() in the _p_e_r_l_s_u_b manpage for
             details.





                                                                       PPPPaaaaggggeeee 33334444






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



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

                 #  0    1    2     3     4    5     6     7     8
                 ($sec,$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 with sunday as day 0.  Also, $year is
             the number of years since 1900, that is, $year is 123 in year
             2023.

             If EXPR is omitted, uses the current time (localtime(time)).

             In a scalar context, returns the _c_t_i_m_e(3) value:

                 $now_string = localtime;  # e.g., "Thu Oct 13 04:54:34 1994"

             This scalar value is nnnnooootttt locale dependent, see the _p_e_r_l_l_o_c_a_l_e
             manpage, but instead a Perl builtin.  Also see the Time::Local
             module, and the _s_t_r_f_t_i_m_e(3) and _m_k_t_i_m_e(3) function available via
             the POSIX module.

     log EXPR

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

     lstat FILEHANDLE

     lstat EXPR

     lstat   Does the same thing as the _s_t_a_t() 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 _s_t_a_t()
             is done.

             If EXPR is omitted, stats $_.

     m//     The match operator.  See the _p_e_r_l_o_p manpage.

     map BLOCK LIST

     map EXPR,LIST
             Evaluates the BLOCK or EXPR for each element of LIST (locally
             setting $_ to each element) and returns the list value composed
             of the results of each such evaluation.  Evaluates BLOCK or EXPR
             in a list context, so each element of LIST may produce zero, one,
             or more elements in the returned value.



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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



                 @chars = map(chr, @nums);

             translates a list of numbers to the corresponding characters.
             And

                 %hash = map { getkey($_) => $_ } @array;

             is just a funny way to write

                 %hash = ();
                 foreach $_ (@array) {
                     $hash{getkey($_)} = $_;
                 }

             Note that, because $_ is a reference into the list 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.  See also the grep entry elsewhere in this
             document for an array composed of those items of the original
             list for which the BLOCK or EXPR evaluates to true.

     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 _m_s_g_c_t_l(2).  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 _m_s_g_g_e_t(2).  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.






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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



     my EXPR A "my" declares the listed variables to be local (lexically) to
             the enclosing block, subroutine, eval, or do/require/use'd file.
             If more than one value is listed, the list must be placed in
             parentheses.  See the section on _P_r_i_v_a_t_e _V_a_r_i_a_b_l_e_s _v_i_a _m_y() in
             the _p_e_r_l_s_u_b manpage for details.

     next LABEL

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

                 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.

     no Module LIST
             See the "use" function, which "no" is the opposite of.

     oct EXPR

     oct     Interprets EXPR as an octal string and returns the corresponding
             value.  (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 Perl or C notation:

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

             If EXPR is omitted, uses $_.  This function is commonly used when
             a string such as "644" needs to be converted into a file mode,
             for example. (Although perl will automatically convert strings
             into numbers as needed, this automatic conversion assumes base
             10.)

     open FILEHANDLE,EXPR

     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.  (Note that lexical variables--those
             declared with my--will not work for this purpose; so if you're
             using my, specify EXPR in your call to open.)

             If the filename begins with '<' or nothing, the file is opened
             for input.  If the filename begins with '>', the file is
             truncated and opened for output.  If the filename begins with



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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



             '>>', 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; thus '+<' is almost always preferred
             for read/write updates--the '+>' mode would clobber the file
             first.  The prefix and the filename may be separated with spaces.
             These various prefixes correspond to the _f_o_p_e_n(3) modes of 'r',
             'r+', 'w', 'w+', 'a', and 'a+'.

             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 See the section on _U_s_i_n_g
             _o_p_e_n() _f_o_r _I_P_C in the _p_e_r_l_i_p_c manpage for more examples of this.
             as command which pipes input to us.  (You may not have a raw
             _o_p_e_n() to a command that pipes both in _a_n_d out, but see the
             _I_P_C::_O_p_e_n_2 manpage, the _I_P_C::_O_p_e_n_3 manpage, and the section on
             _B_i_d_i_r_e_c_t_i_o_n_a_l _C_o_m_m_u_n_i_c_a_t_i_o_n in the _p_e_r_l_i_p_c manpage for
             alternatives.)

             Opening '-' opens STDIN and opening '>-' opens STDOUT.  Open
             returns nonzero upon success, the undefined value otherwise.  If
             the open involved a pipe, the return value happens to be the pid
             of the subprocess.

             If you're unfortunate enough to be running Perl on a system that
             distinguishes between text files and binary files (modern
             operating systems don't care), then you should check out the
             binmode entry elsewhere in this document for tips for dealing
             with this.  The key distinction between systems that need binmode
             and those that don't is their text file formats.  Systems like
             Unix and Plan9 that delimit lines with a single character, and
             that encode that character in C as '\n', do not need binmode.
             The rest need it.

             When opening a file, it's usually a bad idea to continue normal
             execution if the request failed, so open is frequently used in
             connection with die. Even if die won't do what you want (say, in
             a CGI script, where you want to make a nicely formatted error
             message (but there are modules which can help with that problem))
             you should always check the return value from opening a file. The
             infrequent exception is when working with an unopened filehandle
             is actually what you want to do.

             Examples:

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

                 open(LOG, '>>/usr/spool/news/twitlog'); # (log is reserved)
                 # if the open fails, output is discarded





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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



                 open(DBASE, '+<dbase.mine')             # open for update
                     or die "Can't open 'dbase.mine' for update: $!";

                 open(ARTICLE, "caesar <$article |")     # decrypt article
                     or die "Can't start caesar: $!";

                 open(EXTRACT, "|sort >/tmp/Tmp$$")      # $$ is our process id
                     or die "Can't start sort: $!";

                 # process argument list of files along with any includes

                 foreach $file (@ARGV) {
                     process($file, 'fh00');
                 }

                 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 "(.*)"/) {
                             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.  (Duping a filehandle does not
             take into account any existing contents of stdio buffers.)  Here
             is a script that saves, redirects, and restores STDOUT and
             STDERR:

                 #!/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




                                                                       PPPPaaaaggggeeee 33339999






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



                 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 specify "<&=N", where N is a number, then Perl will do an
             equivalent of C's _f_d_o_p_e_n() of that file descriptor; this is more
             parsimonious of file descriptors.  For example:

                 open(FILEHANDLE, "<&=$fd")

             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 whether 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;

             See the section on _S_a_f_e _P_i_p_e _O_p_e_n_s in the _p_e_r_l_i_p_c manpage for
             more examples of this.

             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.

             Closing any piped filehandle causes the parent process to wait
             for the child to finish, and returns the status value in $?.

             Using the constructor from the IO::Handle package (or one of its
             subclasses, such as IO::File or IO::Socket), you can generate
             anonymous filehandles which have the scope of whatever variables
             hold references to them, and automatically close whenever and



                                                                       PPPPaaaaggggeeee 44440000






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



             however you leave that scope:

                 use IO::File;
                 ...
                 sub read_myfile_munged {
                     my $ALL = shift;
                     my $handle = new IO::File;
                     open($handle, "myfile") or die "myfile: $!";
                     $first = <$handle>
                         or return ();     # Automatically closed here.
                     mung $first or die "mung failed";       # Or here.
                     return $first, <$handle> if $ALL;       # Or here.
                     $first;                                 # Or here.
                 }

             The filename that is passed to open will have leading and
             trailing whitespace deleted.  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");

             If you want a "real" C _o_p_e_n() (see the _o_p_e_n(_2) manpage on your
             system), then you should use the _s_y_s_o_p_e_n() function.  This is
             another way to protect your filenames from interpretation.  For
             example:

                 use IO::Handle;
                 sysopen(HANDLE, $path, O_RDWR|O_CREAT|O_EXCL, 0700)
                     or die "sysopen $path: $!";
                 HANDLE->autoflush(1);
                 HANDLE->print("stuff $$\n");
                 seek(HANDLE, 0, 0);
                 print "File contains: ", <HANDLE>;

             See the seek() entry elsewhere in this document for some details
             about mixing reading and writing.

     opendir DIRHANDLE,EXPR
             Opens a directory named EXPR for processing by _r_e_a_d_d_i_r(),
             _t_e_l_l_d_i_r(), _s_e_e_k_d_i_r(), _r_e_w_i_n_d_d_i_r(), and _c_l_o_s_e_d_i_r().  Returns TRUE
             if successful.  DIRHANDLEs have their own namespace separate from
             FILEHANDLEs.

     ord EXPR

     ord     Returns the numeric ascii value of the first character of EXPR.
             If EXPR is omitted, uses $_.  For the reverse, see the chr entry
             elsewhere in this document .





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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



     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.
                 b   A bit string (ascending bit order, like vec()).
                 B   A bit string (descending bit order).
                 h   A hex string (low nybble first).
                 H   A hex string (high nybble first).

                 c   A signed char value.
                 C   An unsigned char value.

                 s   A signed short value.
                 S   An unsigned short value.
                       (This 'short' is _exactly_ 16 bits, which may differ from
                        what a local C compiler calls 'short'.)

                 i   A signed integer value.
                 I   An unsigned integer value.
                       (This 'integer' is _at_least_ 32 bits wide.  Its exact size
                        depends on what a local C compiler calls 'int', and may
                        even be larger than the 'long' described in the next item.)

                 l   A signed long value.
                 L   An unsigned long value.
                       (This 'long' is _exactly_ 32 bits, which may differ from
                        what a local C compiler calls 'long'.)

                 n   A short in "network" (big-endian) order.
                 N   A long in "network" (big-endian) order.
                 v   A short in "VAX" (little-endian) order.
                 V   A long in "VAX" (little-endian) order.
                       (These 'shorts' and 'longs' are _exactly_ 16 bits and
                        _exactly_ 32 bits, respectively.)

                 f   A single-precision float in the native format.
                 d   A double-precision float in the native format.

                 p   A pointer to a null-terminated string.
                 P   A pointer to a structure (fixed-length string).

                 u   A uuencoded string.

                 w   A BER compressed integer.  Its bytes represent an unsigned
                     integer in base 128, most significant digit first, with as few
                     digits as possible.  Bit eight (the high bit) is set on each
                     byte except the last.




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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



                 x   A null byte.
                 X   Back up a byte.
                 @   Null fill to absolute position.

             Each letter may optionally be followed by a number which gives a
             repeat count.  With all types except "a", "A", "b", "B", "h",
             "H", and "P" 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.  The "p" type
             packs a pointer to a null- terminated string.  You are
             responsible for ensuring the string is not a temporary value
             (which can potentially get deallocated before you get around to
             using the packed result).  The "P" packs a pointer to a structure
             of the size indicated by the length. A NULL pointer is created if
             the corresponding value for "p" or "P" is undef.  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 into float and thence back to double
             again 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"




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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



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

                 $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.

     package NAMESPACE
             Declares the compilation unit as being in the given namespace.
             The scope of the package declaration is from the declaration
             itself through the end of the enclosing block (the same scope as
             the _l_o_c_a_l() operator).  All further unqualified dynamic
             identifiers will be in this namespace.  A package statement
             affects only dynamic variables--including those you've used
             _l_o_c_a_l() on--but _n_o_t lexical variables created with _m_y().
             Typically it would be the first declaration in a file to be
             included by the require or use operator.  You can switch into a
             package in more than one place; it influences merely 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 double
             colon:  $Package::Variable.  If the package name is null, the
             main package as assumed.  That is, $::sail is equivalent to
             $main::sail.

             See the section on _P_a_c_k_a_g_e_s in the _p_e_r_l_m_o_d manpage for more
             information about packages, modules, and classes.  See the
             _p_e_r_l_s_u_b manpage for other scoping issues.

     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.

             See the _I_P_C::_O_p_e_n_2 manpage, the _I_P_C::_O_p_e_n_3 manpage, and the
             section on _B_i_d_i_r_e_c_t_i_o_n_a_l _C_o_m_m_u_n_i_c_a_t_i_o_n in the _p_e_r_l_i_p_c manpage for
             examples of such things.

     pop ARRAY

     pop     Pops and returns the last value of the array, shortening the
             array by 1.  Has a similar effect to




                                                                       PPPPaaaaggggeeee 44444444






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



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

             If there are no elements in the array, returns the undefined
             value.  If ARRAY is omitted, pops the @ARGV array in the main
             program, and the @_ array in subroutines, just like _s_h_i_f_t().

     pos SCALAR

     pos     Returns the offset of where the last m//g search left off for the
             variable is in question ($_ is used when the variable is not
             specified).  May be modified to change that offset.  Such
             modification will also influence the \G zero-width assertion in
             regular expressions.  See the _p_e_r_l_r_e manpage and the _p_e_r_l_o_p
             manpage.

     print FILEHANDLE LIST

     print LIST

     print   Prints a string or a comma-separated list of strings.  Returns
             TRUE if successful.  FILEHANDLE may be a scalar variable name, in
             which case the variable contains the name of or a reference to
             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 parentheses around the arguments.)  If FILEHANDLE is
             omitted, prints by default to standard output (or to the last
             selected output channel--see the select entry elsewhere in this
             document ).  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 print takes a LIST,
             anything in the LIST is evaluated in a list context, and any
             subroutine that you call will have one or more of its expressions
             evaluated in a list 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 parentheses around all the arguments.

             Note that if you're storing FILEHANDLES in an array or other
             expression, you will have to use a block returning its value
             instead:

                 print { $files[$i] } "stuff\n";
                 print { $OK ? STDOUT : STDERR } "stuff\n";


     printf FILEHANDLE FORMAT, LIST

     printf FORMAT, LIST
             Equivalent to print FILEHANDLE sprintf(FORMAT, LIST).  The first
             argument of the list will be interpreted as the printf format.
             If use locale is in effect, the character used for the decimal



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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



             point in formatted real numbers is affected by the LC_NUMERIC
             locale.  See the _p_e_r_l_l_o_c_a_l_e manpage.

             Don't fall into the trap of using a _p_r_i_n_t_f() when a simple
             _p_r_i_n_t() would do.  The _p_r_i_n_t() is more efficient, and less error
             prone.

     prototype FUNCTION
             Returns the prototype of a function as a string (or undef if the
             function has no prototype).  FUNCTION is a reference to, or the
             name of, the function whose prototype you want to retrieve.

     push ARRAY,LIST
             Treats ARRAY 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.  Returns the new number of elements in the
             array.

     q/STRING/

     qq/STRING/

     qx/STRING/

     qw/STRING/
             Generalized quotes.  See the _p_e_r_l_o_p manpage.

     quotemeta EXPR

     quotemeta
             Returns the value of EXPR with all non-alphanumeric characters
             backslashed.  (That is, all characters not matching /[A-Za-z_0-
             9]/ will be preceded by a backslash in the returned string,
             regardless of any locale settings.)  This is the internal
             function implementing the \Q escape in double-quoted strings.

             If EXPR is omitted, uses $_.

     rand EXPR

     rand    Returns a random fractional number greater than or equal to 0 and
             less than the value of EXPR.  (EXPR should be positive.)  If EXPR
             is omitted, the value 1 is used.  Automatically calls _s_r_a_n_d()
             unless _s_r_a_n_d() has already been called.  See also _s_r_a_n_d().

             (Note: If your rand function consistently returns numbers that



                                                                       PPPPaaaaggggeeee 44446666






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



             are too large or too small, then your version of Perl was
             probably compiled with the wrong number of RANDBITS.)

     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
             _s_y_s_r_e_a_d().

     readdir DIRHANDLE
             Returns the next directory entry for a directory opened by
             _o_p_e_n_d_i_r().  If used in a list 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
             a list context.

             If you're planning to filetest the return values out of a
             _r_e_a_d_d_i_r(), you'd better prepend the directory in question.
             Otherwise, because we didn't _c_h_d_i_r() there, it would have been
             testing the wrong file.

                 opendir(DIR, $some_dir) || die "can't opendir $some_dir: $!";
                 @dots = grep { /^\./ && -f "$some_dir/$_" } readdir(DIR);
                 closedir DIR;


     readline EXPR
             Reads from the file handle EXPR.  In scalar context, a single
             line is read and returned.  In list context, reads until end-of-
             file is reached and returns a list of lines (however you've
             defined lines with $/ or $INPUT_RECORD_SEPARATOR).  This is the
             internal function implementing the <EXPR> operator, but you can
             use it directly.  The <EXPR> operator is discussed in more detail
             in the section on _I/_O _O_p_e_r_a_t_o_r_s in the _p_e_r_l_o_p manpage.

     readlink EXPR

     readlink
             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 $_.

     readpipe EXPR
             EXPR is interpolated and then executed as a system command.  The
             collected standard output of the command is returned.  In scalar



                                                                       PPPPaaaaggggeeee 44447777






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



             context, it comes back as a single (potentially multi-line)
             string.  In list context, returns a list of lines (however you've
             defined lines with $/ or $INPUT_RECORD_SEPARATOR).  This is the
             internal function implementing the qx/EXPR/ operator, but you can
             use it directly.  The qx/EXPR/ operator is discussed in more
             detail in the section on _I/_O _O_p_e_r_a_t_o_r_s in the _p_e_r_l_o_p manpage.

     recv SOCKET,SCALAR,LEN,FLAGS
             Receives a message on a socket.  Attempts to receive LENGTH bytes
             of data into variable SCALAR from the specified SOCKET
             filehandle.  Actually does a C _r_e_c_v_f_r_o_m(), so that it can returns
             the address of the sender.  Returns 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.  See the section on _U_D_P: _M_e_s_s_a_g_e _P_a_s_s_i_n_g in the
             _p_e_r_l_i_p_c manpage for examples.

     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;
                 }


     ref EXPR

     ref     Returns a TRUE value if EXPR is a reference, FALSE otherwise.  If
             EXPR is not specified, $_ will be used.  The value returned
             depends on the type of thing the reference is a reference to.
             Builtin types include:






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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



                 REF
                 SCALAR
                 ARRAY
                 HASH
                 CODE
                 GLOB

             If the referenced object has been blessed into a package, then
             that package name is returned instead.  You can think of _r_e_f() as
             a _t_y_p_e_o_f() operator.

                 if (ref($r) eq "HASH") {
                     print "r is a reference to a hash.\n";
                 }
                 if (!ref ($r) {
                     print "r is not a reference at all.\n";
                 }

             See also the _p_e_r_l_r_e_f manpage.

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

     require EXPR

     require Demands some semantics specified by EXPR, or by $_ if EXPR is not
             supplied.  If EXPR is numeric, demands that the current version
             of Perl ($] or $PERL_VERSION) be equal or greater than EXPR.

             Otherwise, demands that a library file be included if it hasn't
             already been included.  The file is included via the do-FILE
             mechanism, which is essentially just a variety of _e_v_a_l().  Has
             semantics similar to the following subroutine:





















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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



                 sub require {
                     local($filename) = @_;
                     return 1 if $INC{$filename};
                     local($realfilename,$result);
                     ITER: {
                         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.  But it's better just to put the
             "1;", in case you add more statements.

             If EXPR is a bareword, the require assumes a "._p_m" extension and
             replaces "::" with "/" in the filename for you, to make it easy
             to load standard modules.  This form of loading of modules does
             not risk altering your namespace.

             For a yet-more-powerful import facility, see the use entry
             elsewhere in this document and the _p_e_r_l_m_o_d manpage.

     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.  Resets only 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

             Resetting "A-Z" is not recommended because you'll wipe out your
             ARGV and ENV arrays.  Resets only package variables--lexical



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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



             variables are unaffected, but they clean themselves up on scope
             exit anyway, so you'll probably want to use them instead.  See
             the my entry elsewhere in this document .

     return EXPR

     return  Returns from a subroutine, _e_v_a_l(), or do FILE with the value of
             the given EXPR.  Evaluation of EXPR may be in a list, scalar, or
             void context, depending on how the return value will be used, and
             the context may vary from one execution to the next (see
             _w_a_n_t_a_r_r_a_y()).  If no EXPR is given, returns an empty list in a
             list context, an undefined value in a scalar context, or nothing
             in a void context.

             (Note that in the absence of a return, a subroutine, eval, or do
             FILE will automatically return the value of the last expression
             evaluated.)

     reverse LIST
             In a list context, returns a list value consisting of the
             elements of LIST in the opposite order.  In a scalar context,
             concatenates the elements of LIST, and returns a string value
             consisting of those bytes, but in the opposite order.

                 print reverse <>;           # line tac, last line first

                 undef $/;                   # for efficiency of <>
                 print scalar reverse <>;    # byte tac, last line tsrif

             This operator is also handy for inverting a hash, although there
             are some caveats.  If a value is duplicated in the original hash,
             only one of those can be represented as a key in the inverted
             hash.  Also, this has to unwind one hash and build a whole new
             one, which may take some time on a large hash.

                 %by_name = reverse %by_address;     # Invert the hash


     rewinddir DIRHANDLE
             Sets the current position to the beginning of the directory for
             the _r_e_a_d_d_i_r() 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





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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



     rmdir   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///    The substitution operator.  See the _p_e_r_l_o_p manpage.

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

                 @counts = ( scalar @a, scalar @b, scalar @c );

             There is no equivalent operator to force an expression to be
             interpolated in a list context because it's in practice never
             needed.  If you really wanted to do so, however, you could use
             the construction @{[ (some expression) ]}, but usually a simple
             (some expression) suffices.

     seek FILEHANDLE,POSITION,WHENCE
             Sets FILEHANDLE's position, just like the _f_s_e_e_k() call of stdio.
             FILEHANDLE may be an expression whose value gives the name of the
             filehandle.  The values for WHENCE are 0 to set the new position
             to POSITION, 1 to set it to the current position plus POSITION,
             and 2 to set it to EOF plus POSITION (typically negative).  For
             WHENCE you may use the constants SEEK_SET, SEEK_CUR, and SEEK_END
             from either the IO::Seekable or the POSIX module.  Returns 1 upon
             success, 0 otherwise.

             If you want to position file for _s_y_s_r_e_a_d() or _s_y_s_w_r_i_t_e(), don't
             use _s_e_e_k() -- buffering makes its effect on the file's system
             position unpredictable and non-portable.  Use _s_y_s_s_e_e_k() instead.

             On some systems you have to do a seek whenever you switch between
             reading and writing.  Amongst other things, this may have the
             effect of calling stdio's _c_l_e_a_r_e_r_r(3).  A WHENCE of 1 (SEEK_CUR)
             is useful for not moving the file position:

                 seek(TEST,0,1);

             This is also useful for applications emulating tail -f.  Once you
             hit EOF on your read, and then sleep for a while, you might have
             to stick in a _s_e_e_k() to reset things.  The _s_e_e_k() doesn't change
             the current position, but it _d_o_e_s clear the end-of-file condition
             on the handle, so that the next <FILE> makes Perl try again to
             read something.  We hope.

             If that doesn't work (some stdios are particularly cantankerous),
             then you may need something more like this:







                                                                       PPPPaaaaggggeeee 55552222






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



                 for (;;) {
                     for ($curpos = tell(FILE); $_ = <FILE>; $curpos = tell(FILE)) {
                         # search for some stuff and put it into files
                     }
                     sleep($for_a_while);
                     seek(FILE, $curpos, 0);
                 }


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

             Some programmers may prefer to think of filehandles as objects
             with methods, preferring to write the last example as:

                 use IO::Handle;
                 STDERR->autoflush(1);


     select RBITS,WBITS,EBITS,TIMEOUT
             This calls the _s_e_l_e_c_t(2) system call with the bit masks
             specified, which can be constructed using _f_i_l_e_n_o() and _v_e_c(),
             along these lines:

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




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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



             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);

             or to block until something becomes ready just do this

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

             Most systems do not bother to return anything useful in
             $timeleft, so calling _s_e_l_e_c_t() in a scalar context just returns
             $nfound.

             Any of the bit masks 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.

             You can effect a sleep of 250 milliseconds this way:

                 select(undef, undef, undef, 0.25);

             WWWWAAAARRRRNNNNIIIINNNNGGGG: Do not attempt to mix buffered I/O (like _r_e_a_d() or <FH>)
             with _s_e_l_e_c_t().  You have to use _s_y_s_r_e_a_d() instead.

     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,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



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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



             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, in which case it does a C _s_e_n_d_t_o().
             Returns the number of characters sent, or the undefined value if
             there is an error.  See the section on _U_D_P: _M_e_s_s_a_g_e _P_a_s_s_i_n_g in
             the _p_e_r_l_i_p_c manpage for examples.

     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 _s_e_t_p_g_r_p(2).  If the arguments are omitted,
             it defaults to 0,0.  Note that the POSIX version of _s_e_t_p_g_r_p()
             does not accept any arguments, so only setpgrp 0,0 is portable.

     setpriority WHICH,WHO,PRIORITY
             Sets the current priority for a process, a process group, or a
             user.  (See _s_e_t_p_r_i_o_r_i_t_y(2).)  Will produce a fatal error if used
             on a machine that doesn't implement _s_e_t_p_r_i_o_r_i_t_y(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   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 _u_n_s_h_i_f_t(), _p_u_s_h(), and _p_o_p().  _S_h_i_f_t() and _u_n_s_h_i_f_t() do
             the same thing to the left end of an array that _p_o_p() and _p_u_s_h()
             do to the right end.






                                                                       PPPPaaaaggggeeee 55555555






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



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

             For the inverse sine operation, you may use the _P_O_S_I_X::_a_s_i_n()
             function, or use this relation:

                 sub asin { atan2($_[0], sqrt(1 - $_[0] * $_[0])) }


     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 _a_l_a_r_m() and _s_l_e_e_p() calls, because _s_l_e_e_p() is often
             implemented using _a_l_a_r_m().

             On some older systems, it may sleep up to a full second less than
             what you requested, depending on how it counts seconds.  Most
             modern systems always sleep the full amount.

             For delays of finer granularity than one second, you may use
             Perl's _s_y_s_c_a_l_l() interface to access _s_e_t_i_t_i_m_e_r(2) if your system
             supports it, or else see the select() entry elsewhere in this



                                                                       PPPPaaaaggggeeee 55556666






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



             document below.

             See also the POSIX module's _s_i_g_p_a_u_s_e() function.

     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 should "use
             Socket;" first to get the proper definitions imported.  See the
             example in the section on _S_o_c_k_e_t_s: _C_l_i_e_n_t/_S_e_r_v_e_r _C_o_m_m_u_n_i_c_a_t_i_o_n in
             the _p_e_r_l_i_p_c manpage.

     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.  Returns TRUE if successful.

     sort SUBNAME LIST

     sort BLOCK LIST

     sort LIST
             Sorts the LIST and returns the sorted list value.  If SUBNAME or
             BLOCK is omitted, sorts in standard string comparison order.  If
             SUBNAME is specified, it 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.)  SUBNAME may be a scalar variable name, in which case
             the value provides the name of the subroutine to use.  In place
             of a SUBNAME, 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 the package global variables $a and $b (see example
             below).  They are passed by reference, so don't modify $a and $b.
             And don't try to declare them as lexicals either.

             You also cannot exit out of the sort block or subroutine using
             any of the loop control operators described in the _p_e_r_l_s_y_n
             manpage or with _g_o_t_o().

             When use locale is in effect, sort LIST sorts LIST according to
             the current collation locale.  See the _p_e_r_l_l_o_c_a_l_e manpage.

             Examples:





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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



                 # sort lexically
                 @articles = sort @files;

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

                 # now case-insensitively
                 @articles = sort {uc($a) cmp uc($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 numeric
                 }
                 @sortedclass = sort byage @class;

                 # this sorts the %age hash by value instead of key
                 # using an in-line function
                 @eldest = sort { $age{$b} <=> $age{$a} } keys %age;

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

                 # inefficiently sort by descending numeric compare using
                 # the first integer after the first = sign, or the
                 # whole record case-insensitively otherwise

                 @new = sort {
                     ($b =~ /=(\d+)/)[0] <=> ($a =~ /=(\d+)/)[0]
                                         ||
                                 uc($a)  cmp  uc($b)
                 } @old;








                                                                       PPPPaaaaggggeeee 55558888






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



                 # same thing, but much more efficiently;
                 # we'll build auxiliary indices instead
                 # for speed
                 @nums = @caps = ();
                 for (@old) {
                     push @nums, /=(\d+)/;
                     push @caps, uc($_);
                 }

                 @new = @old[ sort {
                                     $nums[$b] <=> $nums[$a]
                                              ||
                                     $caps[$a] cmp $caps[$b]
                                    } 0..$#old
                            ];

                 # same thing using a Schwartzian Transform (no temps)
                 @new = map { $_->[0] }
                     sort { $b->[1] <=> $a->[1]
                                     ||
                            $a->[2] cmp $b->[2]
                     } map { [$_, /=(\d+)/, uc($_)] } @old;

             If you're using strict, you _M_U_S_T _N_O_T declare $a and $b as
             lexicals.  They are package globals.  That means if you're in the
             main package, it's

                 @articles = sort {$main::b <=> $main::a} @files;

             or just

                 @articles = sort {$::b <=> $::a} @files;

             but if you're in the FooPack package, it's

                 @articles = sort {$FooPack::b <=> $FooPack::a} @files;

             The comparison function is required to behave.  If it returns
             inconsistent results (sometimes saying $x[1] is less than $x[2]
             and sometimes saying the opposite, for example) the Perl
             interpreter will probably crash and dump core.  This is entirely
             due to and dependent upon your system's _q_s_o_r_t(3) library routine;
             this routine often avoids sanity checks in the interest of speed.

     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



                                                                       PPPPaaaaggggeeee 55559999






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



             shrinks as necessary.  If LENGTH is omitted, removes everything
             from OFFSET onward.  The following equivalences 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 list 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

     split /PATTERN/,EXPR

     split /PATTERN/

     split   Splits a string into an array of strings, and returns it.

             If not in a list context, returns the number of fields found and
             splits into the @_ array.  (In a list context, you can force the
             split into @_ by using ?? as the pattern delimiters, but it still
             returns the array value.)  The use of implicit split to @_ is
             deprecated, however.

             If EXPR is omitted, splits the $_ string.  If PATTERN is also
             omitted, splits on whitespace (after skipping any leading
             whitespace).  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 and is not negative, 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 _p_o_p() would do well to remember).  If LIMIT is
             negative, it is treated as if an arbitrarily large LIMIT had been
             specified.

             A pattern matching the null string (not to be confused with a



                                                                       PPPPaaaaggggeeee 66660000






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



             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 split a line partially

                 ($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", 3);

             produces the list value

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

             If you had the entire header of a normal Unix email message in
             $header, you could split it up into fields and their values this
             way:

                 $header =~ s/\n\s+/ /g;  # fix continuation lines
                 %hdrs   =  (UNIX_FROM => split /^(\S*?):\s*/m, $header);

             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 PATTERN of space (' ') will split
             on white space just as split with no arguments does.  Thus,
             _s_p_l_i_t(' ') can be used to emulate aaaawwwwkkkk's default behavior, whereas
             split(/ /) will give you as many null initial fields as there are
             leading spaces.  A split on /\s+/ is like a _s_p_l_i_t(' ') except
             that any leading whitespace produces a null first field.  A split
             with no arguments really does a split(' ', $_) internally.

             Example:







                                                                       PPPPaaaaggggeeee 66661111






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



                 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 the
             chop, chomp,  and join entries elsewhere in this document .)

     sprintf FORMAT, LIST
             Returns a string formatted by the usual printf conventions of the
             C library function _s_p_r_i_n_t_f().  See the _s_p_r_i_n_t_f(_3) manpage or the
             _p_r_i_n_t_f(_3) manpage on your system for an explanation of the
             general principles.

             Perl does all of its own _s_p_r_i_n_t_f() formatting -- it emulates the
             C function _s_p_r_i_n_t_f(), but it doesn't use it (except for
             floating-point numbers, and even then only the standard modifiers
             are allowed).  As a result, any non-standard extensions in your
             local _s_p_r_i_n_t_f() are not available from Perl.

             Perl's _s_p_r_i_n_t_f() permits the following universally-known
             conversions:

                %%   a percent sign
                %c   a character with the given number
                %s   a string
                %d   a signed integer, in decimal
                %u   an unsigned integer, in decimal
                %o   an unsigned integer, in octal
                %x   an unsigned integer, in hexadecimal
                %e   a floating-point number, in scientific notation
                %f   a floating-point number, in fixed decimal notation
                %g   a floating-point number, in %e or %f notation

             In addition, Perl permits the following widely-supported
             conversions:

                %X   like %x, but using upper-case letters
                %E   like %e, but using an upper-case "E"
                %G   like %g, but with an upper-case "E" (if applicable)
                %p   a pointer (outputs the Perl value's address in hexadecimal)
                %n   special: *stores* the number of characters output so far
                     into the next variable in the parameter list

             Finally, for backward (and we do mean "backward") compatibility,
             Perl permits these unnecessary but widely-supported conversions:







                                                                       PPPPaaaaggggeeee 66662222






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



                %i   a synonym for %d
                %D   a synonym for %ld
                %U   a synonym for %lu
                %O   a synonym for %lo
                %F   a synonym for %f

             Perl permits the following universally-known flags between the %
             and the conversion letter:

                space   prefix positive number with a space
                +       prefix positive number with a plus sign
                -       left-justify within the field
                0       use zeros, not spaces, to right-justify
                #       prefix octal with "0", hex with "0x"
                number  minimum field width
                .number "precision": digits after decimal point for floating-point,
                        max length for string, minimum length for integer
                l       interpret integer as C type "long" or "unsigned long"
                h       interpret integer as C type "short" or "unsigned short"

             There is also one Perl-specific flag:

                V       interpret integer as Perl's standard integer type

             Where a number would appear in the flags, an asterisk ("*") may
             be used instead, in which case Perl uses the next item in the
             parameter list as the given number (that is, as the field width
             or precision).  If a field width obtained through "*" is
             negative, it has the same effect as the '-' flag: left-
             justification.

             If use locale is in effect, the character used for the decimal
             point in formatted real numbers is affected by the LC_NUMERIC
             locale.  See the _p_e_r_l_l_o_c_a_l_e manpage.

     sqrt EXPR

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

     srand EXPR

     srand   Sets the random number seed for the rand operator.  If EXPR is
             omitted, uses a semi-random value based on the current time and
             process ID, among other things.  In versions of Perl prior to
             5.004 the default seed was just the current _t_i_m_e().  This isn't a
             particularly good seed, so many old programs supply their own
             seed value (often time ^ $$ or C<time ^ ($$ + ($$ << 15))>), but
             that isn't necessary any more.

             In fact, it's usually not necessary to call _s_r_a_n_d() at all,
             because if it is not called explicitly, it is called implicitly



                                                                       PPPPaaaaggggeeee 66663333






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



             at the first use of the rand operator.  However, this was not the
             case in version of Perl before 5.004, so if your script will run
             under older Perl versions, it should call _s_r_a_n_d().

             Note that you need something much more random than the default
             seed for cryptographic purposes.  Checksumming the compressed
             output of one or more rapidly changing operating system status
             programs is the usual method.  For example:

                 srand (time ^ $$ ^ unpack "%L*", `ps axww | gzip`);

             If you're particularly concerned with this, see the
             Math::TrulyRandom module in CPAN.

             Do _n_o_t call _s_r_a_n_d() multiple times in your program unless you
             know exactly what you're doing and why you're doing it.  The
             point of the function is to "seed" the _r_a_n_d() function so that
             _r_a_n_d() can produce a different sequence each time you run your
             program.  Just do it once at the top of your program, or you
             _w_o_n'_t get random numbers out of _r_a_n_d()!

             Frequently called programs (like CGI scripts) that simply use

                 time ^ $$

             for a seed can fall prey to the mathematical property that

                 a^b == (a+1)^(b+1)

             one-third of the time.  So don't do that.

     stat FILEHANDLE

     stat EXPR

     stat    Returns a 13-element array giving the status info for a file,
             either the file opened via FILEHANDLE, or named by EXPR.  If EXPR
             is omitted, it stats $_.  Returns a null list if the stat fails.
             Typically used as follows:

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

             Not all fields are supported on all filesystem types.  Here are
             the meaning of the fields:









                                                                       PPPPaaaaggggeeee 66664444






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



               0 dev      device number of filesystem
               1 ino      inode number
               2 mode     file mode  (type and permissions)
               3 nlink    number of (hard) links to the file
               4 uid      numeric user ID of file's owner
               5 gid      numeric group ID of file's owner
               6 rdev     the device identifier (special files only)
               7 size     total size of file, in bytes
               8 atime    last access time since the epoch
               9 mtime    last modify time since the epoch
              10 ctime    inode change time (NOT creation time!) since the epoch
              11 blksize  preferred block size for file system I/O
              12 blocks   actual number of blocks allocated

             (The epoch was at 00:00 January 1, 1970 GMT.)

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

     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 run times 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:






                                                                       PPPPaaaaggggeeee 66665555






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



                 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 _f_g_r_e_p(1).  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 delimiter
                 foreach $file (sort keys(%seen)) {
                     print $file, "\n";
                 }


     sub BLOCK

     sub NAME

     sub NAME BLOCK
             This is subroutine definition, not a real function _p_e_r _s_e.  With
             just a NAME (and possibly prototypes), it's just a forward
             declaration.  Without a NAME, it's an anonymous function
             declaration, and does actually return a value: the CODE ref of
             the closure you just created.  See the _p_e_r_l_s_u_b manpage and the
             _p_e_r_l_r_e_f manpage for details.






                                                                       PPPPaaaaggggeeee 66666666






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



     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 (but don't do that).
             If OFFSET is negative (or more precisely, less than $[), starts
             that far from the end of the string.  If LEN is omitted, returns
             everything to the end of the string.  If LEN is negative, leaves
             that many characters off the end of the string.

             If you specify a substring which is partly outside the string,
             the part within the string is returned.    If the substring is
             totally outside the string a warning is produced.

             You can use the _s_u_b_s_t_r() function as an lvalue, in which case
             EXPR must be an lvalue.  If you assign something shorter than
             LEN, the string will shrink, 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 _s_p_r_i_n_t_f().

     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
             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);

             Note that Perl supports passing of up to only 14 arguments to
             your system call, which in practice should usually suffice.

             Syscall returns whatever value returned by the system call it
             calls.  If the system call fails, syscall returns -1 and sets $!
             (errno).  Note that some system calls can legitimately return -1.
             The proper way to handle such calls is to assign $!=0; before the



                                                                       PPPPaaaaggggeeee 66667777






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



             call and check the value of <$!> if syscall returns -1.

             There's a problem with syscall(&SYS_pipe): it returns the file
             number of the read end of the pipe it creates.  There is no way
             to retrieve the file number of the other end.  You can avoid this
             problem by using pipe instead.

     sysopen FILEHANDLE,FILENAME,MODE

     sysopen FILEHANDLE,FILENAME,MODE,PERMS
             Opens the file whose filename is given by FILENAME, and
             associates it with FILEHANDLE.  If FILEHANDLE is an expression,
             its value is used as the name of the real filehandle wanted.
             This function calls the underlying operating system's open
             function with the parameters FILENAME, MODE, PERMS.

             The possible values and flag bits of the MODE parameter are
             system-dependent; they are available via the standard module
             Fcntl.  However, for historical reasons, some values are
             universal: zero means read-only, one means write-only, and two
             means read/write.

             If the file named by FILENAME does not exist and the open call
             creates it (typically because MODE includes the O_CREAT flag),
             then the value of PERMS specifies the permissions of the newly
             created file.  If PERMS is omitted, the default value is 0666,
             which allows read and write for all.  This default is reasonable:
             see umask.

             The IO::File module provides a more object-oriented approach, if
             you're into that kind of thing.

     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 _r_e_a_d(2).  It
             bypasses stdio, so mixing this with other kinds of reads,
             _p_r_i_n_t(), _w_r_i_t_e(), _s_e_e_k(), or _t_e_l_l() can cause confusion because
             stdio usually buffers data.  Returns the number of bytes actually
             read, or undef if there was an error.  SCALAR will be grown or
             shrunk so that the last byte actually read is the last byte of
             the scalar after the read.

             An OFFSET may be specified to place the read data at some place
             in the string other than the beginning.  A negative OFFSET
             specifies placement at that many bytes counting backwards from
             the end of the string.  A positive OFFSET greater than the length
             of SCALAR results in the string being padded to the required size
             with "\0" bytes before the result of the read is appended.





                                                                       PPPPaaaaggggeeee 66668888






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



     sysseek FILEHANDLE,POSITION,WHENCE
             Sets FILEHANDLE's system position using the system call _l_s_e_e_k(2).
             It bypasses stdio, so mixing this with reads (other than
             _s_y_s_r_e_a_d()), _p_r_i_n_t(), _w_r_i_t_e(), _s_e_e_k(), or _t_e_l_l() may cause
             confusion.  FILEHANDLE may be an expression whose value gives the
             name of the filehandle.  The values for WHENCE are 0 to set the
             new position to POSITION, 1 to set the it to the current position
             plus POSITION, and 2 to set it to EOF plus POSITION (typically
             negative).  For WHENCE, you may use the constants SEEK_SET,
             SEEK_CUR, and SEEK_END from either the IO::Seekable or the POSIX
             module.

             Returns the new position, or the undefined value on failure.  A
             position of zero is returned as the string "0 but true"; thus
             _s_y_s_s_e_e_k() returns TRUE on success and FALSE on failure, yet you
             can still easily determine the new position.

     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 _w_a_i_t() call.  To get the actual exit
             value divide by 256.  See also the exec entry elsewhere in this
             document .  This is _N_O_T what you want to use to capture the
             output from a command, for that you should use merely backticks
             or qx//, as described in the section on `_S_T_R_I_N_G` in the _p_e_r_l_o_p
             manpage.

             Because _s_y_s_t_e_m() and backticks block SIGINT and SIGQUIT, killing
             the program they're running doesn't actually interrupt your
             program.

                 @args = ("command", "arg1", "arg2");
                 system(@args) == 0
                      or die "system @args failed: $?"

             Here's a more elaborate example of analysing the return value
             from _s_y_s_t_e_m() on a Unix system to check for all possibilities,
             including for signals and core dumps.















                                                                       PPPPaaaaggggeeee 66669999






PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



                 $rc = 0xffff & system @args;
                 printf "system(%s) returned %#04x: ", "@args", $rc;
                 if ($rc == 0) {
                     print "ran with normal exit\n";
                 }
                 elsif ($rc == 0xff00) {
                     print "command failed: $!\n";
                 }
                 elsif ($rc > 0x80) {
                     $rc >>= 8;
                     print "ran with non-zero exit status $rc\n";
                 }
                 else {
                     print "ran with ";
                     if ($rc &   0x80) {
                         $rc &= ~0x80;
                         print "core dump from ";
                     }
                     print "signal $rc\n"
                 }
                 $ok = ($rc != 0);

             When the arguments get executed via the system shell, results
             will be subject to its quirks and capabilities.  See the section
             on `_S_T_R_I_N_G` in the _p_e_r_l_o_p manpage for details.

     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 _w_r_i_t_e(2).  It
             bypasses stdio, so mixing this with reads (other than _s_y_s_r_e_a_d()),
             _p_r_i_n_t(), _w_r_i_t_e(), _s_e_e_k(), or _t_e_l_l() may cause confusion because
             stdio usually buffers data.  Returns the number of bytes actually
             written, or undef if there was an error.  If the LENGTH is
             greater than the available data in the SCALAR after the OFFSET,
             only as much data as is available will be written.

             An OFFSET may be specified to write the data from some part of
             the string other than the beginning.  A negative OFFSET specifies
             writing that many bytes counting backwards from the end of the
             string.  In the case the SCALAR is empty you can use OFFSET but
             only zero offset.

     tell FILEHANDLE

     tell    Returns the current 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.





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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



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

     tie VARIABLE,CLASSNAME,LIST
             This function binds a variable to a package class that will
             provide the implementation for the variable.  VARIABLE is the
             name of the variable to be enchanted.  CLASSNAME is the name of a
             class implementing objects of correct type.  Any additional
             arguments are passed to the "new" method of the class (meaning
             TIESCALAR, TIEARRAY, or TIEHASH).  Typically these are arguments
             such as might be passed to the _d_b_m__o_p_e_n() function of C.  The
             object returned by the "new" method is also returned by the _t_i_e()
             function, which would be useful if you want to access other
             methods in CLASSNAME.

             Note that functions such as _k_e_y_s() and _v_a_l_u_e_s() may return huge
             array values when used on large objects, like DBM files.  You may
             prefer to use the _e_a_c_h() function to iterate over such.  Example:

                 # print out history file offsets
                 use NDBM_File;
                 tie(%HIST, 'NDBM_File', '/usr/lib/news/history', 1, 0);
                 while (($key,$val) = each %HIST) {
                     print $key, ' = ', unpack('L',$val), "\n";
                 }
                 untie(%HIST);

             A class implementing a hash should have the following methods:

                 TIEHASH classname, LIST
                 DESTROY this
                 FETCH this, key
                 STORE this, key, value
                 DELETE this, key
                 EXISTS this, key
                 FIRSTKEY this
                 NEXTKEY this, lastkey

             A class implementing an ordinary array should have the following
             methods:

                 TIEARRAY classname, LIST
                 DESTROY this
                 FETCH this, key
                 STORE this, key, value
                 [others TBD]

             A class implementing a scalar should have the following methods:



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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



                 TIESCALAR classname, LIST
                 DESTROY this
                 FETCH this,
                 STORE this, value

             Unlike _d_b_m_o_p_e_n(), the _t_i_e() function will not use or require a
             module for you--you need to do that explicitly yourself.  See the
             _D_B__F_i_l_e manpage or the _C_o_n_f_i_g module for interesting _t_i_e()
             implementations.

     tied VARIABLE
             Returns a reference to the object underlying VARIABLE (the same
             value that was originally returned by the _t_i_e() call which bound
             the variable to a package.)  Returns the undefined value if
             VARIABLE isn't tied to a package.

     time    Returns the number of non-leap seconds since whatever time the
             system considers to be the epoch (that's 00:00:00, January 1,
             1904 for MacOS, and 00:00:00 UTC, January 1, 1970 for most other
             systems).  Suitable for feeding to _g_m_t_i_m_e() and _l_o_c_a_l_t_i_m_e().

     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;


     tr///   The translation operator.  Same as y///. See the _p_e_r_l_o_p manpage.

     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.

     uc EXPR

     uc      Returns an uppercased version of EXPR.  This is the internal
             function implementing the \U escape in double-quoted strings.
             Respects current LC_CTYPE locale if use locale in force.  See the
             _p_e_r_l_l_o_c_a_l_e manpage.

             If EXPR is omitted, uses $_.

     ucfirst EXPR

     ucfirst Returns the value of EXPR with the first character uppercased.
             This is the internal function implementing the \u escape in
             double-quoted strings.  Respects current LC_CTYPE locale if use
             locale in force.  See the _p_e_r_l_l_o_c_a_l_e manpage.




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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



             If EXPR is omitted, uses $_.

     umask EXPR

     umask   Sets the umask for the process to EXPR and returns the previous
             value.  If EXPR is omitted, merely returns the current umask.
             Remember that a umask is a number, usually given in octal; it is
             _n_o_t a string of octal digits.  See also the oct entry elsewhere
             in this document if all you have is a string.

     undef EXPR

     undef   Undefines the value of EXPR, which must be an lvalue.  Use only
             on a scalar value, an entire array, an entire hash, or a
             subroutine name (using "&").  (Using _u_n_d_e_f() will probably not do
             what you expect on most predefined variables or DBM list values,
             so don't do that.)  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, assign to a variable or pass as a parameter.
             Examples:

                 undef $foo;
                 undef $bar{'blurfl'};             # Compare to: delete $bar{'blurfl'};
                 undef @ary;
                 undef %hash;
                 undef &mysub;
                 return (wantarray ? (undef, $errmsg) : undef) if $they_blew_it;
                 select undef, undef, undef, 0.25;
                 ($a, $b, undef, $c) = &foo;       # Ignore third value returned


     unlink LIST

     unlink  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.

             If LIST is omitted, uses $_.

     unpack TEMPLATE,EXPR
             Unpack does the reverse of pack: it takes a string representing a
             structure and expands it out into a list value, returning the
             array value.  (In a scalar context, it returns merely the first



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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



             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 ordinal { unpack("c",$_[0]); } # same as ord()

             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;

             The following efficiently counts the number of set bits in a bit
             vector:

                 $setbits = unpack("%32b*", $selectmask);


     untie VARIABLE
             Breaks the binding between a variable and a package.  (See
             _t_i_e().)

     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 new number of elements in the array.

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

             Note the LIST is prepended whole, not one element at a time, so
             the prepended elements stay in the same order.  Use reverse to do
             the reverse.

     use Module LIST

     use Module

     use Module VERSION LIST






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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



     use VERSION
             Imports some semantics into the current package from the named
             module, generally by aliasing certain subroutine or variable
             names into your package.  It is exactly equivalent to

                 BEGIN { require Module; import Module LIST; }

             except that Module _m_u_s_t be a bareword.

             If the first argument to use is a number, it is treated as a
             version number instead of a module name.  If the version of the
             Perl interpreter is less than VERSION, then an error message is
             printed and Perl exits immediately.  This is often useful if you
             need to check the current Perl version before useing library
             modules which have changed in incompatible ways from older
             versions of Perl.  (We try not to do this more than we have to.)

             The BEGIN forces the require and import to happen at compile
             time.  The require makes sure the module is loaded into memory if
             it hasn't been yet.  The import is not a builtin--it's just an
             ordinary static method call into the "Module" package to tell the
             module to import the list of features back into the current
             package.  The module can implement its import method any way it
             likes, though most modules just choose to derive their import
             method via inheritance from the Exporter class that is defined in
             the Exporter module.  See the _E_x_p_o_r_t_e_r manpage.  If no import
             method can be found then the error is currently silently ignored.
             This may change to a fatal error in a future version.

             If you don't want your namespace altered, explicitly supply an
             empty list:

                 use Module ();

             That is exactly equivalent to

                 BEGIN { require Module; }

             If the VERSION argument is present between Module and LIST, then
             the use will call the VERSION method in class Module with the
             given version as an argument.  The default VERSION method,
             inherited from the Universal class, croaks if the given version
             is larger than the value of the variable $Module::VERSION.  (Note
             that there is not a comma after VERSION!)

             Because this is a wide-open interface, pragmas (compiler
             directives) are also implemented this way.  Currently implemented
             pragmas are:







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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



                 use integer;
                 use diagnostics;
                 use sigtrap qw(SEGV BUS);
                 use strict  qw(subs vars refs);
                 use subs    qw(afunc blurfl);

             These pseudo-modules import semantics into the current block
             scope, unlike ordinary modules, which import symbols into the
             current package (which are effective through the end of the
             file).

             There's a corresponding "no" command that unimports meanings
             imported by use, i.e., it calls unimport Module LIST instead of
             import.

                 no integer;
                 no strict 'refs';

             If no unimport method can be found the call fails with a fatal
             error.

             See the _p_e_r_l_m_o_d manpage for a list of standard modules and
             pragmas.

     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:

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


     values HASH
             Returns a normal array consisting of all the values of the named
             hash.  (In a scalar context, returns the number of values.)  The
             values are returned in an apparently random order, but it is the
             same order as either the _k_e_y_s() or _e_a_c_h() function would produce
             on the same hash.  As a side effect, it resets HASH's iterator.
             See also _k_e_y_s(), _e_a_c_h(), and _s_o_r_t().

     vec EXPR,OFFSET,BITS
             Treats the string in EXPR as a vector of unsigned integers, and
             returns the value of the bit field specified by OFFSET.  BITS
             specifies the number of bits that are reserved for each entry in
             the bit vector.  This must be a power of two from 1 to 32. _v_e_c()
             may also be assigned to, in which case parentheses are needed to
             give the expression the correct precedence as in



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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



                 vec($image, $max_x * $x + $y, 8) = 3;

             Vectors created with _v_e_c() can also be manipulated with the
             logical operators |, &, and ^, which will assume a bit vector
             operation is desired when both operands are strings.

             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

                 use POSIX ":sys_wait_h";
                 ...
                 waitpid(-1,&WNOHANG);

             then you can do a non-blocking wait for any process.  Non-
             blocking wait is available on machines supporting either the
             _w_a_i_t_p_i_d(2) or _w_a_i_t_4(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 a list value.  Returns FALSE if the context is
             looking for a scalar.  Returns the undefined value if the context
             is looking for no value (void context).

                 return unless defined wantarray;    # don't bother doing more
                 my @a = complex_calculation();
                 return wantarray ? @a : "@a";


     warn LIST
             Produces a message on STDERR just like _d_i_e(), but doesn't exit or
             throw an exception.

             No message is printed if there is a $SIG{__WARN__} handler



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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



             installed.  It is the handler's responsibility to deal with the
             message as it sees fit (like, for instance, converting it into a
             _d_i_e()).  Most handlers must therefore make arrangements to
             actually display the warnings that they are not prepared to deal
             with, by calling _w_a_r_n() again in the handler.  Note that this is
             quite safe and will not produce an endless loop, since __WARN__
             hooks are not called from inside one.

             You will find this behavior is slightly different from that of
             $SIG{__DIE__} handlers (which don't suppress the error text, but
             can instead call _d_i_e() again to change it).

             Using a __WARN__ handler provides a powerful way to silence all
             warnings (even the so-called mandatory ones).  An example:

                 # wipe out *all* compile-time warnings
                 BEGIN { $SIG{'__WARN__'} = sub { warn $_[0] if $DOWARN } }
                 my $foo = 10;
                 my $foo = 20;          # no warning about duplicate my $foo,
                                        # but hey, you asked for it!
                 # no compile-time or run-time warnings before here
                 $DOWARN = 1;

                 # run-time warnings enabled after here
                 warn "\$foo is alive and $foo!";     # does show up

             See the _p_e_r_l_v_a_r manpage for details on setting %SIG entries, and
             for more examples.

     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 as the
             filehandle, but the format for the current output channel (see
             the _s_e_l_e_c_t() function) 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 dynamically
             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



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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))



             output channel, which starts out as STDOUT but may be changed by
             the select operator.  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 _p_e_r_l_f_o_r_m manpage.

             Note that write is _N_O_T the opposite of read.  Unfortunately.

     y///    The translation operator.  Same as tr///.  See the _p_e_r_l_o_p
             manpage.













































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PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))                                                        PPPPEEEERRRRLLLLFFFFUUUUNNNNCCCC((((1111))))























































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