3 perlvar - Perl predefined variables
7 =head2 The Syntax of Variable Names
9 Variable names in Perl can have several formats. Usually, they
10 must begin with a letter or underscore, in which case they can be
11 arbitrarily long (up to an internal limit of 251 characters) and
12 may contain letters, digits, underscores, or the special sequence
13 C<::> or C<'>. In this case, the part before the last C<::> or
14 C<'> is taken to be a I<package qualifier>; see L<perlmod>.
15 A Unicode letter that is not ASCII is not considered to be a letter
16 unless S<C<"use utf8">> is in effect, and somewhat more complicated
17 rules apply; see L<perldata/Identifier parsing> for details.
19 Perl variable names may also be a sequence of digits, a single
20 punctuation character, or the two-character sequence: C<^> (caret or
21 CIRCUMFLEX ACCENT) followed by any one of the characters C<[][A-Z^_?\]>.
22 These names are all reserved for
23 special uses by Perl; for example, the all-digits names are used
24 to hold data captured by backreferences after a regular expression
27 Since Perl v5.6.0, Perl variable names may also be alphanumeric strings
28 preceded by a caret. These must all be written in the form C<${^Foo}>;
29 the braces are not optional. C<${^Foo}> denotes the scalar variable
30 whose name is considered to be a control-C<F> followed by two C<o>'s.
32 reserved for future special uses by Perl, except for the ones that
33 begin with C<^_> (caret-underscore). No
34 name that begins with C<^_> will acquire a special
35 meaning in any future version of Perl; such names may therefore be
36 used safely in programs. C<$^_> itself, however, I<is> reserved.
38 Perl identifiers that begin with digits or
39 punctuation characters are exempt from the effects of the C<package>
40 declaration and are always forced to be in package C<main>; they are
41 also exempt from C<strict 'vars'> errors. A few other names are also
50 In particular, the special C<${^_XYZ}> variables are always taken
51 to be in package C<main>, regardless of any C<package> declarations
54 =head1 SPECIAL VARIABLES
56 The following names have special meaning to Perl. Most punctuation
57 names have reasonable mnemonics, or analogs in the shells.
58 Nevertheless, if you wish to use long variable names, you need only say:
62 at the top of your program. This aliases all the short names to the long
63 names in the current package. Some even have medium names, generally
64 borrowed from B<awk>. For more info, please see L<English>.
66 Before you continue, note the sort order for variables. In general, we
67 first list the variables in case-insensitive, almost-lexigraphical
68 order (ignoring the C<{> or C<^> preceding words, as in C<${^UNICODE}>
69 or C<$^T>), although C<$_> and C<@_> move up to the top of the pile.
70 For variables with the same identifier, we list it in order of scalar,
71 array, hash, and bareword.
73 =head2 General Variables
82 The default input and pattern-searching space. The following pairs are
85 while (<>) {...} # equivalent only in while!
86 while (defined($_ = <>)) {...}
97 Here are the places where Perl will assume C<$_> even if you don't use it:
103 The following functions use C<$_> as a default argument:
105 abs, alarm, chomp, chop, chr, chroot,
106 cos, defined, eval, evalbytes, exp, fc, glob, hex, int, lc,
107 lcfirst, length, log, lstat, mkdir, oct, ord, pos, print, printf,
108 quotemeta, readlink, readpipe, ref, require, reverse (in scalar context only),
109 rmdir, say, sin, split (for its second
110 argument), sqrt, stat, study, uc, ucfirst,
115 All file tests (C<-f>, C<-d>) except for C<-t>, which defaults to STDIN.
120 The pattern matching operations C<m//>, C<s///> and C<tr///> (aka C<y///>)
121 when used without an C<=~> operator.
125 The default iterator variable in a C<foreach> loop if no other
126 variable is supplied.
130 The implicit iterator variable in the C<grep()> and C<map()> functions.
134 The implicit variable of C<given()>.
138 The default place to put the next value or input record
139 when a C<< <FH> >>, C<readline>, C<readdir> or C<each>
140 operation's result is tested by itself as the sole criterion of a C<while>
141 test. Outside a C<while> test, this will not happen.
145 C<$_> is a global variable.
147 However, between perl v5.10.0 and v5.24.0, it could be used lexically by
148 writing C<my $_>. Making C<$_> refer to the global C<$_> in the same scope
149 was then possible with C<our $_>. This experimental feature was removed and is
150 now a fatal error, but you may encounter it in older code.
152 Mnemonic: underline is understood in certain operations.
159 Within a subroutine the array C<@_> contains the parameters passed to
160 that subroutine. Inside a subroutine, C<@_> is the default array for
161 the array operators C<pop> and C<shift>.
165 =item $LIST_SEPARATOR
168 X<$"> X<$LIST_SEPARATOR>
170 When an array or an array slice is interpolated into a double-quoted
171 string or a similar context such as C</.../>, its elements are
172 separated by this value. Default is a space. For example, this:
174 print "The array is: @array\n";
176 is equivalent to this:
178 print "The array is: " . join($", @array) . "\n";
180 Mnemonic: works in double-quoted context.
187 X<$$> X<$PID> X<$PROCESS_ID>
189 The process number of the Perl running this script. Though you I<can> set
190 this variable, doing so is generally discouraged, although it can be
191 invaluable for some testing purposes. It will be reset automatically
192 across C<fork()> calls.
194 Note for Linux and Debian GNU/kFreeBSD users: Before Perl v5.16.0 perl
195 would emulate POSIX semantics on Linux systems using LinuxThreads, a
196 partial implementation of POSIX Threads that has since been superseded
197 by the Native POSIX Thread Library (NPTL).
199 LinuxThreads is now obsolete on Linux, and caching C<getpid()>
200 like this made embedding perl unnecessarily complex (since you'd have
201 to manually update the value of $$), so now C<$$> and C<getppid()>
202 will always return the same values as the underlying C library.
204 Debian GNU/kFreeBSD systems also used LinuxThreads up until and
205 including the 6.0 release, but after that moved to FreeBSD thread
206 semantics, which are POSIX-like.
208 To see if your system is affected by this discrepancy check if
209 C<getconf GNU_LIBPTHREAD_VERSION | grep -q NPTL> returns a false
210 value. NTPL threads preserve the POSIX semantics.
212 Mnemonic: same as shells.
217 X<$0> X<$PROGRAM_NAME>
219 Contains the name of the program being executed.
221 On some (but not all) operating systems assigning to C<$0> modifies
222 the argument area that the C<ps> program sees. On some platforms you
223 may have to use special C<ps> options or a different C<ps> to see the
224 changes. Modifying the C<$0> is more useful as a way of indicating the
225 current program state than it is for hiding the program you're
228 Note that there are platform-specific limitations on the maximum
229 length of C<$0>. In the most extreme case it may be limited to the
230 space occupied by the original C<$0>.
232 In some platforms there may be arbitrary amount of padding, for
233 example space characters, after the modified name as shown by C<ps>.
234 In some platforms this padding may extend all the way to the original
235 length of the argument area, no matter what you do (this is the case
236 for example with Linux 2.2).
238 Note for BSD users: setting C<$0> does not completely remove "perl"
239 from the ps(1) output. For example, setting C<$0> to C<"foobar"> may
240 result in C<"perl: foobar (perl)"> (whether both the C<"perl: "> prefix
241 and the " (perl)" suffix are shown depends on your exact BSD variant
242 and version). This is an operating system feature, Perl cannot help it.
244 In multithreaded scripts Perl coordinates the threads so that any
245 thread may modify its copy of the C<$0> and the change becomes visible
246 to ps(1) (assuming the operating system plays along). Note that
247 the view of C<$0> the other threads have will not change since they
248 have their own copies of it.
250 If the program has been given to perl via the switches C<-e> or C<-E>,
251 C<$0> will contain the string C<"-e">.
253 On Linux as of perl v5.14.0 the legacy process name will be set with
254 C<prctl(2)>, in addition to altering the POSIX name via C<argv[0]> as
255 perl has done since version 4.000. Now system utilities that read the
256 legacy process name such as ps, top and killall will recognize the
257 name you set when assigning to C<$0>. The string you supply will be
258 cut off at 16 bytes, this is a limitation imposed by Linux.
260 Mnemonic: same as B<sh> and B<ksh>.
267 X<$(> X<$GID> X<$REAL_GROUP_ID>
269 The real gid of this process. If you are on a machine that supports
270 membership in multiple groups simultaneously, gives a space separated
271 list of groups you are in. The first number is the one returned by
272 C<getgid()>, and the subsequent ones by C<getgroups()>, one of which may be
273 the same as the first number.
275 However, a value assigned to C<$(> must be a single number used to
276 set the real gid. So the value given by C<$(> should I<not> be assigned
277 back to C<$(> without being forced numeric, such as by adding zero. Note
278 that this is different to the effective gid (C<$)>) which does take a
281 You can change both the real gid and the effective gid at the same
282 time by using C<POSIX::setgid()>. Changes
283 to C<$(> require a check to C<$!>
284 to detect any possible errors after an attempted change.
286 Mnemonic: parentheses are used to I<group> things. The real gid is the
287 group you I<left>, if you're running setgid.
289 =item $EFFECTIVE_GROUP_ID
294 X<$)> X<$EGID> X<$EFFECTIVE_GROUP_ID>
296 The effective gid of this process. If you are on a machine that
297 supports membership in multiple groups simultaneously, gives a space
298 separated list of groups you are in. The first number is the one
299 returned by C<getegid()>, and the subsequent ones by C<getgroups()>,
300 one of which may be the same as the first number.
302 Similarly, a value assigned to C<$)> must also be a space-separated
303 list of numbers. The first number sets the effective gid, and
304 the rest (if any) are passed to C<setgroups()>. To get the effect of an
305 empty list for C<setgroups()>, just repeat the new effective gid; that is,
306 to force an effective gid of 5 and an effectively empty C<setgroups()>
307 list, say C< $) = "5 5" >.
309 You can change both the effective gid and the real gid at the same
310 time by using C<POSIX::setgid()> (use only a single numeric argument).
311 Changes to C<$)> require a check to C<$!> to detect any possible errors
312 after an attempted change.
314 C<< $< >>, C<< $> >>, C<$(> and C<$)> can be set only on
315 machines that support the corresponding I<set[re][ug]id()> routine. C<$(>
316 and C<$)> can be swapped only on machines supporting C<setregid()>.
318 Mnemonic: parentheses are used to I<group> things. The effective gid
319 is the group that's I<right> for you, if you're running setgid.
326 X<< $< >> X<$UID> X<$REAL_USER_ID>
328 The real uid of this process. You can change both the real uid and the
329 effective uid at the same time by using C<POSIX::setuid()>. Since
330 changes to C<< $< >> require a system call, check C<$!> after a change
331 attempt to detect any possible errors.
333 Mnemonic: it's the uid you came I<from>, if you're running setuid.
335 =item $EFFECTIVE_USER_ID
340 X<< $> >> X<$EUID> X<$EFFECTIVE_USER_ID>
342 The effective uid of this process. For example:
344 $< = $>; # set real to effective uid
345 ($<,$>) = ($>,$<); # swap real and effective uids
347 You can change both the effective uid and the real uid at the same
348 time by using C<POSIX::setuid()>. Changes to C<< $> >> require a check
349 to C<$!> to detect any possible errors after an attempted change.
351 C<< $< >> and C<< $> >> can be swapped only on machines
352 supporting C<setreuid()>.
354 Mnemonic: it's the uid you went I<to>, if you're running setuid.
356 =item $SUBSCRIPT_SEPARATOR
361 X<$;> X<$SUBSEP> X<SUBSCRIPT_SEPARATOR>
363 The subscript separator for multidimensional array emulation. If you
364 refer to a hash element as
370 $foo{join($;, $x, $y, $z)}
374 @foo{$x,$y,$z} # a slice--note the @
378 ($foo{$x},$foo{$y},$foo{$z})
380 Default is "\034", the same as SUBSEP in B<awk>. If your keys contain
381 binary data there might not be any safe value for C<$;>.
383 Consider using "real" multidimensional arrays as described
386 Mnemonic: comma (the syntactic subscript separator) is a semi-semicolon.
393 Special package variables when using C<sort()>, see L<perlfunc/sort>.
394 Because of this specialness C<$a> and C<$b> don't need to be declared
395 (using C<use vars>, or C<our()>) even when using the C<strict 'vars'>
396 pragma. Don't lexicalize them with C<my $a> or C<my $b> if you want to
397 be able to use them in the C<sort()> comparison block or function.
402 The hash C<%ENV> contains your current environment. Setting a
403 value in C<ENV> changes the environment for any child processes
404 you subsequently C<fork()> off.
406 As of v5.18.0, both keys and values stored in C<%ENV> are stringified.
410 if( ref $ENV{'bar'} ) {
411 say "Pre 5.18.0 Behaviour";
413 say "Post 5.18.0 Behaviour";
416 Previously, only child processes received stringified values:
421 # Always printed 'non ref'
423 q/print ( ref $ENV{'bar'} ? 'ref' : 'non ref' ) /);
425 This happens because you can't really share arbitrary data structures with
428 =item $OLD_PERL_VERSION
431 X<$]> X<$OLD_PERL_VERSION>
433 The revision, version, and subversion of the Perl interpreter, represented
434 as a decimal of the form 5.XXXYYY, where XXX is the version / 1e3 and YYY
435 is the subversion / 1e6. For example, Perl v5.10.1 would be "5.010001".
437 This variable can be used to determine whether the Perl interpreter
438 executing a script is in the right range of versions:
440 warn "No PerlIO!\n" if $] lt '5.008';
442 When comparing C<$]>, string comparison operators are B<highly
443 recommended>. The inherent limitations of binary floating point
444 representation can sometimes lead to incorrect comparisons for some
445 numbers on some architectures.
447 See also the documentation of C<use VERSION> and C<require VERSION>
448 for a convenient way to fail if the running Perl interpreter is too old.
450 See L</$^V> for a representation of the Perl version as a L<version>
451 object, which allows more flexible string comparisons.
453 The main advantage of C<$]> over C<$^V> is that it works the same on any
454 version of Perl. The disadvantages are that it can't easily be compared
455 to versions in other formats (e.g. literal v-strings, "v1.2.3" or
456 version objects) and numeric comparisons can occasionally fail; it's good
457 for string literal version checks and bad for comparing to a variable
458 that hasn't been sanity-checked.
460 The C<$OLD_PERL_VERSION> form was added in Perl v5.20.0 for historical
461 reasons but its use is discouraged. (If your reason to use C<$]> is to
462 run code on old perls then referring to it as C<$OLD_PERL_VERSION> would
465 Mnemonic: Is this version of perl in the right bracket?
470 X<$^F> X<$SYSTEM_FD_MAX>
472 The maximum system file descriptor, ordinarily 2. System file
473 descriptors are passed to C<exec()>ed processes, while higher file
474 descriptors are not. Also, during an
475 C<open()>, system file descriptors are
476 preserved even if the C<open()> fails (ordinary file descriptors are
477 closed before the C<open()> is attempted). The close-on-exec
478 status of a file descriptor will be decided according to the value of
479 C<$^F> when the corresponding file, pipe, or socket was opened, not the
480 time of the C<exec()>.
485 The array C<@F> contains the fields of each line read in when autosplit
486 mode is turned on. See L<perlrun> for the B<-a> switch. This array
487 is package-specific, and must be declared or given a full package name
488 if not in package main when running under C<strict 'vars'>.
493 The array C<@INC> contains the list of places that the C<do EXPR>,
494 C<require>, or C<use> constructs look for their library files. It
495 initially consists of the arguments to any B<-I> command-line
496 switches, followed by the default Perl library, probably
497 F</usr/local/lib/perl>.
498 Prior to Perl 5.26, C<.> -which represents the current directory, was included
499 in C<@INC>; it has been removed. This change in behavior is documented
500 in L<C<PERL_USE_UNSAFE_INC>|perlrun/PERL_USE_UNSAFE_INC> and it is
501 not recommended that C<.> be re-added to C<@INC>.
502 If you need to modify C<@INC> at runtime, you should use the C<use lib> pragma
503 to get the machine-dependent library properly loaded as well:
505 use lib '/mypath/libdir/';
508 You can also insert hooks into the file inclusion system by putting Perl
509 code directly into C<@INC>. Those hooks may be subroutine references,
510 array references or blessed objects. See L<perlfunc/require> for details.
515 The hash C<%INC> contains entries for each filename included via the
516 C<do>, C<require>, or C<use> operators. The key is the filename
517 you specified (with module names converted to pathnames), and the
518 value is the location of the file found. The C<require>
519 operator uses this hash to determine whether a particular file has
520 already been included.
522 If the file was loaded via a hook (e.g. a subroutine reference, see
523 L<perlfunc/require> for a description of these hooks), this hook is
524 by default inserted into C<%INC> in place of a filename. Note, however,
525 that the hook may have set the C<%INC> entry by itself to provide some more
531 X<$^I> X<$INPLACE_EDIT>
533 The current value of the inplace-edit extension. Use C<undef> to disable
536 Mnemonic: value of B<-i> switch.
541 Each package contains a special array called C<@ISA> which contains a list
542 of that class's parent classes, if any. This array is simply a list of
543 scalars, each of which is a string that corresponds to a package name. The
544 array is examined when Perl does method resolution, which is covered in
547 To load packages while adding them to C<@ISA>, see the L<parent> pragma. The
548 discouraged L<base> pragma does this as well, but should not be used except
549 when compatibility with the discouraged L<fields> pragma is required.
554 By default, running out of memory is an untrappable, fatal error.
555 However, if suitably built, Perl can use the contents of C<$^M>
556 as an emergency memory pool after C<die()>ing. Suppose that your Perl
557 were compiled with C<-DPERL_EMERGENCY_SBRK> and used Perl's malloc.
560 $^M = 'a' x (1 << 16);
562 would allocate a 64K buffer for use in an emergency. See the
563 F<INSTALL> file in the Perl distribution for information on how to
564 add custom C compilation flags when compiling perl. To discourage casual
565 use of this advanced feature, there is no L<English|English> long name for
568 This variable was added in Perl 5.004.
575 The name of the operating system under which this copy of Perl was
576 built, as determined during the configuration process. For examples
577 see L<perlport/PLATFORMS>.
579 The value is identical to C<$Config{'osname'}>. See also L<Config>
580 and the B<-V> command-line switch documented in L<perlrun>.
582 In Windows platforms, C<$^O> is not very helpful: since it is always
583 C<MSWin32>, it doesn't tell the difference between
584 95/98/ME/NT/2000/XP/CE/.NET. Use C<Win32::GetOSName()> or
585 Win32::GetOSVersion() (see L<Win32> and L<perlport>) to distinguish
586 between the variants.
588 This variable was added in Perl 5.003.
593 The hash C<%SIG> contains signal handlers for signals. For example:
595 sub handler { # 1st argument is signal name
597 print "Caught a SIG$sig--shutting down\n";
602 $SIG{'INT'} = \&handler;
603 $SIG{'QUIT'} = \&handler;
605 $SIG{'INT'} = 'DEFAULT'; # restore default action
606 $SIG{'QUIT'} = 'IGNORE'; # ignore SIGQUIT
608 Using a value of C<'IGNORE'> usually has the effect of ignoring the
609 signal, except for the C<CHLD> signal. See L<perlipc> for more about
612 Here are some other examples:
614 $SIG{"PIPE"} = "Plumber"; # assumes main::Plumber (not
616 $SIG{"PIPE"} = \&Plumber; # just fine; assume current
618 $SIG{"PIPE"} = *Plumber; # somewhat esoteric
619 $SIG{"PIPE"} = Plumber(); # oops, what did Plumber()
622 Be sure not to use a bareword as the name of a signal handler,
623 lest you inadvertently call it.
625 If your system has the C<sigaction()> function then signal handlers
626 are installed using it. This means you get reliable signal handling.
628 The default delivery policy of signals changed in Perl v5.8.0 from
629 immediate (also known as "unsafe") to deferred, also known as "safe
630 signals". See L<perlipc> for more information.
632 Certain internal hooks can be also set using the C<%SIG> hash. The
633 routine indicated by C<$SIG{__WARN__}> is called when a warning
634 message is about to be printed. The warning message is passed as the
635 first argument. The presence of a C<__WARN__> hook causes the
636 ordinary printing of warnings to C<STDERR> to be suppressed. You can
637 use this to save warnings in a variable, or turn warnings into fatal
640 local $SIG{__WARN__} = sub { die $_[0] };
643 As the C<'IGNORE'> hook is not supported by C<__WARN__>, you can
644 disable warnings using the empty subroutine:
646 local $SIG{__WARN__} = sub {};
648 The routine indicated by C<$SIG{__DIE__}> is called when a fatal
649 exception is about to be thrown. The error message is passed as the
650 first argument. When a C<__DIE__> hook routine returns, the exception
651 processing continues as it would have in the absence of the hook,
652 unless the hook routine itself exits via a C<goto &sub>, a loop exit,
653 or a C<die()>. The C<__DIE__> handler is explicitly disabled during
654 the call, so that you can die from a C<__DIE__> handler. Similarly
657 The C<$SIG{__DIE__}> hook is called even inside an C<eval()>. It was
658 never intended to happen this way, but an implementation glitch made
659 this possible. This used to be deprecated, as it allowed strange action
660 at a distance like rewriting a pending exception in C<$@>. Plans to
661 rectify this have been scrapped, as users found that rewriting a
662 pending exception is actually a useful feature, and not a bug.
664 C<__DIE__>/C<__WARN__> handlers are very special in one respect: they
665 may be called to report (probable) errors found by the parser. In such
666 a case the parser may be in inconsistent state, so any attempt to
667 evaluate Perl code from such a handler will probably result in a
668 segfault. This means that warnings or errors that result from parsing
669 Perl should be used with extreme caution, like this:
671 require Carp if defined $^S;
672 Carp::confess("Something wrong") if defined &Carp::confess;
673 die "Something wrong, but could not load Carp to give "
675 . "To see backtrace try starting Perl with -MCarp switch";
677 Here the first line will load C<Carp> I<unless> it is the parser who
678 called the handler. The second line will print backtrace and die if
679 C<Carp> was available. The third line will be executed only if C<Carp> was
682 Having to even think about the C<$^S> variable in your exception
683 handlers is simply wrong. C<$SIG{__DIE__}> as currently implemented
684 invites grievous and difficult to track down errors. Avoid it
685 and use an C<END{}> or CORE::GLOBAL::die override instead.
687 See L<perlfunc/die>, L<perlfunc/warn>, L<perlfunc/eval>, and
688 L<warnings> for additional information.
695 The time at which the program began running, in seconds since the
696 epoch (beginning of 1970). The values returned by the B<-M>, B<-A>,
697 and B<-C> filetests are based on this value.
702 X<$^V> X<$PERL_VERSION>
704 The revision, version, and subversion of the Perl interpreter,
705 represented as a L<version> object.
707 This variable first appeared in perl v5.6.0; earlier versions of perl
708 will see an undefined value. Before perl v5.10.0 C<$^V> was represented
709 as a v-string rather than a L<version> object.
711 C<$^V> can be used to determine whether the Perl interpreter executing
712 a script is in the right range of versions. For example:
714 warn "Hashes not randomized!\n" if !$^V or $^V lt v5.8.1
716 While version objects overload stringification, to portably convert
717 C<$^V> into its string representation, use C<sprintf()>'s C<"%vd">
718 conversion, which works for both v-strings or version objects:
720 printf "version is v%vd\n", $^V; # Perl's version
722 See the documentation of C<use VERSION> and C<require VERSION>
723 for a convenient way to fail if the running Perl interpreter is too old.
725 See also C<L</$]>> for a decimal representation of the Perl version.
727 The main advantage of C<$^V> over C<$]> is that, for Perl v5.10.0 or
728 later, it overloads operators, allowing easy comparison against other
729 version representations (e.g. decimal, literal v-string, "v1.2.3", or
730 objects). The disadvantage is that prior to v5.10.0, it was only a
731 literal v-string, which can't be easily printed or compared, whereas
732 the behavior of C<$]> is unchanged on all versions of Perl.
734 Mnemonic: use ^V for a version object.
736 =item ${^WIN32_SLOPPY_STAT}
737 X<${^WIN32_SLOPPY_STAT}> X<sitecustomize> X<sitecustomize.pl>
739 If this variable is set to a true value, then C<stat()> on Windows will
740 not try to open the file. This means that the link count cannot be
741 determined and file attributes may be out of date if additional
742 hardlinks to the file exist. On the other hand, not opening the file
743 is considerably faster, especially for files on network drives.
745 This variable could be set in the F<sitecustomize.pl> file to
746 configure the local Perl installation to use "sloppy" C<stat()> by
747 default. See the documentation for B<-f> in
748 L<perlrun|perlrun/"Command Switches"> for more information about site
751 This variable was added in Perl v5.10.0.
753 =item $EXECUTABLE_NAME
756 X<$^X> X<$EXECUTABLE_NAME>
758 The name used to execute the current copy of Perl, from C's
759 C<argv[0]> or (where supported) F</proc/self/exe>.
761 Depending on the host operating system, the value of C<$^X> may be
762 a relative or absolute pathname of the perl program file, or may
763 be the string used to invoke perl but not the pathname of the
764 perl program file. Also, most operating systems permit invoking
765 programs that are not in the PATH environment variable, so there
766 is no guarantee that the value of C<$^X> is in PATH. For VMS, the
767 value may or may not include a version number.
769 You usually can use the value of C<$^X> to re-invoke an independent
770 copy of the same perl that is currently running, e.g.,
772 @first_run = `$^X -le "print int rand 100 for 1..100"`;
774 But recall that not all operating systems support forking or
775 capturing of the output of commands, so this complex statement
778 It is not safe to use the value of C<$^X> as a path name of a file,
779 as some operating systems that have a mandatory suffix on
780 executable files do not require use of the suffix when invoking
781 a command. To convert the value of C<$^X> to a path name, use the
782 following statements:
784 # Build up a set of file names (not command names).
788 $this_perl .= $Config{_exe}
789 unless $this_perl =~ m/$Config{_exe}$/i;
792 Because many operating systems permit anyone with read access to
793 the Perl program file to make a copy of it, patch the copy, and
794 then execute the copy, the security-conscious Perl programmer
795 should take care to invoke the installed copy of perl, not the
796 copy referenced by C<$^X>. The following statements accomplish
797 this goal, and produce a pathname that can be invoked as a
798 command or referenced as a file.
801 my $secure_perl_path = $Config{perlpath};
803 $secure_perl_path .= $Config{_exe}
804 unless $secure_perl_path =~ m/$Config{_exe}$/i;
809 =head2 Variables related to regular expressions
811 Most of the special variables related to regular expressions are side
812 effects. Perl sets these variables when it has a successful match, so
813 you should check the match result before using them. For instance:
815 if( /P(A)TT(ER)N/ ) {
816 print "I found $1 and $2\n";
819 These variables are read-only and dynamically-scoped, unless we note
822 The dynamic nature of the regular expression variables means that
823 their value is limited to the block that they are in, as demonstrated
826 my $outer = 'Wallace and Grommit';
827 my $inner = 'Mutt and Jeff';
829 my $pattern = qr/(\S+) and (\S+)/;
831 sub show_n { print "\$1 is $1; \$2 is $2\n" }
835 show_n() if $outer =~ m/$pattern/;
838 show_n() if $inner =~ m/$pattern/;
844 The output shows that while in the C<OUTER> block, the values of C<$1>
845 and C<$2> are from the match against C<$outer>. Inside the C<INNER>
846 block, the values of C<$1> and C<$2> are from the match against
847 C<$inner>, but only until the end of the block (i.e. the dynamic
848 scope). After the C<INNER> block completes, the values of C<$1> and
849 C<$2> return to the values for the match against C<$outer> even though
850 we have not made another match:
852 $1 is Wallace; $2 is Grommit
853 $1 is Mutt; $2 is Jeff
854 $1 is Wallace; $2 is Grommit
856 =head3 Performance issues
858 Traditionally in Perl, any use of any of the three variables C<$`>, C<$&>
859 or C<$'> (or their C<use English> equivalents) anywhere in the code, caused
860 all subsequent successful pattern matches to make a copy of the matched
861 string, in case the code might subsequently access one of those variables.
862 This imposed a considerable performance penalty across the whole program,
863 so generally the use of these variables has been discouraged.
865 In Perl 5.6.0 the C<@-> and C<@+> dynamic arrays were introduced that
866 supply the indices of successful matches. So you could for example do
871 print $`, $&, $'; # bad: performance hit
873 print # good: no performance hit
874 substr($str, 0, $-[0]),
875 substr($str, $-[0], $+[0]-$-[0]),
878 In Perl 5.10.0 the C</p> match operator flag and the C<${^PREMATCH}>,
879 C<${^MATCH}>, and C<${^POSTMATCH}> variables were introduced, that allowed
880 you to suffer the penalties only on patterns marked with C</p>.
882 In Perl 5.18.0 onwards, perl started noting the presence of each of the
883 three variables separately, and only copied that part of the string
886 $`; $&; "abcdefgh" =~ /d/
888 perl would only copy the "abcd" part of the string. That could make a big
889 difference in something like
891 $str = 'x' x 1_000_000;
893 $str =~ /x/g # one char copied a million times, not a million chars
895 In Perl 5.20.0 a new copy-on-write system was enabled by default, which
896 finally fixes all performance issues with these three variables, and makes
897 them safe to use anywhere.
899 The C<Devel::NYTProf> and C<Devel::FindAmpersand> modules can help you
900 find uses of these problematic match variables in your code.
904 =item $<I<digits>> ($1, $2, ...)
905 X<$1> X<$2> X<$3> X<$I<digits>>
907 Contains the subpattern from the corresponding set of capturing
908 parentheses from the last successful pattern match, not counting patterns
909 matched in nested blocks that have been exited already.
911 Note there is a distinction between a capture buffer which matches
912 the empty string a capture buffer which is optional. Eg, C<(x?)> and
913 C<(x)?> The latter may be undef, the former not.
915 These variables are read-only and dynamically-scoped.
917 Mnemonic: like \digits.
920 X<@{^CAPTURE}> X<@^CAPTURE>
922 An array which exposes the contents of the capture buffers, if any, of
923 the last successful pattern match, not counting patterns matched
924 in nested blocks that have been exited already.
926 Note that the 0 index of @{^CAPTURE} is equivalent to $1, the 1 index
927 is equivalent to $2, etc.
929 if ("foal"=~/(.)(.)(.)(.)/) {
930 print join "-", @{^CAPTURE};
933 should output "f-o-a-l".
935 See also L<<< /$<I<digits>> ($1, $2, ...) >>>, L</%{^CAPTURE}> and
938 Note that unlike most other regex magic variables there is no single
939 letter equivalent to C<@{^CAPTURE}>.
941 This variable was added in 5.25.7
948 The string matched by the last successful pattern match (not counting
949 any matches hidden within a BLOCK or C<eval()> enclosed by the current
952 See L</Performance issues> above for the serious performance implications
953 of using this variable (even once) in your code.
955 This variable is read-only and dynamically-scoped.
957 Mnemonic: like C<&> in some editors.
962 This is similar to C<$&> (C<$MATCH>) except that it does not incur the
963 performance penalty associated with that variable.
965 See L</Performance issues> above.
967 In Perl v5.18 and earlier, it is only guaranteed
968 to return a defined value when the pattern was compiled or executed with
969 the C</p> modifier. In Perl v5.20, the C</p> modifier does nothing, so
970 C<${^MATCH}> does the same thing as C<$MATCH>.
972 This variable was added in Perl v5.10.0.
974 This variable is read-only and dynamically-scoped.
979 X<$`> X<$PREMATCH> X<${^PREMATCH}>
981 The string preceding whatever was matched by the last successful
982 pattern match, not counting any matches hidden within a BLOCK or C<eval>
983 enclosed by the current BLOCK.
985 See L</Performance issues> above for the serious performance implications
986 of using this variable (even once) in your code.
988 This variable is read-only and dynamically-scoped.
990 Mnemonic: C<`> often precedes a quoted string.
993 X<$`> X<${^PREMATCH}>
995 This is similar to C<$`> ($PREMATCH) except that it does not incur the
996 performance penalty associated with that variable.
998 See L</Performance issues> above.
1000 In Perl v5.18 and earlier, it is only guaranteed
1001 to return a defined value when the pattern was compiled or executed with
1002 the C</p> modifier. In Perl v5.20, the C</p> modifier does nothing, so
1003 C<${^PREMATCH}> does the same thing as C<$PREMATCH>.
1005 This variable was added in Perl v5.10.0.
1007 This variable is read-only and dynamically-scoped.
1012 X<$'> X<$POSTMATCH> X<${^POSTMATCH}> X<@->
1014 The string following whatever was matched by the last successful
1015 pattern match (not counting any matches hidden within a BLOCK or C<eval()>
1016 enclosed by the current BLOCK). Example:
1018 local $_ = 'abcdefghi';
1020 print "$`:$&:$'\n"; # prints abc:def:ghi
1022 See L</Performance issues> above for the serious performance implications
1023 of using this variable (even once) in your code.
1025 This variable is read-only and dynamically-scoped.
1027 Mnemonic: C<'> often follows a quoted string.
1030 X<${^POSTMATCH}> X<$'> X<$POSTMATCH>
1032 This is similar to C<$'> (C<$POSTMATCH>) except that it does not incur the
1033 performance penalty associated with that variable.
1035 See L</Performance issues> above.
1037 In Perl v5.18 and earlier, it is only guaranteed
1038 to return a defined value when the pattern was compiled or executed with
1039 the C</p> modifier. In Perl v5.20, the C</p> modifier does nothing, so
1040 C<${^POSTMATCH}> does the same thing as C<$POSTMATCH>.
1042 This variable was added in Perl v5.10.0.
1044 This variable is read-only and dynamically-scoped.
1046 =item $LAST_PAREN_MATCH
1049 X<$+> X<$LAST_PAREN_MATCH>
1051 The text matched by the highest used capture group of the last
1052 successful search pattern. It is logically equivalent to the highest
1053 numbered capture variable (C<$1>, C<$2>, ...) which has a defined value.
1055 This is useful if you don't know which one of a set of alternative patterns
1056 matched. For example:
1058 /Version: (.*)|Revision: (.*)/ && ($rev = $+);
1060 This variable is read-only and dynamically-scoped.
1062 Mnemonic: be positive and forward looking.
1064 =item $LAST_SUBMATCH_RESULT
1067 X<$^N> X<$LAST_SUBMATCH_RESULT>
1069 The text matched by the used group most-recently closed (i.e. the group
1070 with the rightmost closing parenthesis) of the last successful search
1071 pattern. This is subtly different from C<$+>. For example in
1073 "ab" =~ /^((.)(.))$/
1077 $1,$^N have the value "ab"
1078 $2 has the value "a"
1079 $3,$+ have the value "b"
1081 This is primarily used inside C<(?{...})> blocks for examining text
1082 recently matched. For example, to effectively capture text to a variable
1083 (in addition to C<$1>, C<$2>, etc.), replace C<(...)> with
1085 (?:(...)(?{ $var = $^N }))
1087 By setting and then using C<$var> in this way relieves you from having to
1088 worry about exactly which numbered set of parentheses they are.
1090 This variable was added in Perl v5.8.0.
1092 Mnemonic: the (possibly) Nested parenthesis that most recently closed.
1094 =item @LAST_MATCH_END
1097 X<@+> X<@LAST_MATCH_END>
1099 This array holds the offsets of the ends of the last successful
1100 submatches in the currently active dynamic scope. C<$+[0]> is
1101 the offset into the string of the end of the entire match. This
1102 is the same value as what the C<pos> function returns when called
1103 on the variable that was matched against. The I<n>th element
1104 of this array holds the offset of the I<n>th submatch, so
1105 C<$+[1]> is the offset past where C<$1> ends, C<$+[2]> the offset
1106 past where C<$2> ends, and so on. You can use C<$#+> to determine
1107 how many subgroups were in the last successful match. See the
1108 examples given for the C<@-> variable.
1110 This variable was added in Perl v5.6.0.
1114 =item %LAST_PAREN_MATCH
1117 X<%+> X<%LAST_PAREN_MATCH> X<%{^CAPTURE}>
1119 Similar to C<@+>, the C<%+> hash allows access to the named capture
1120 buffers, should they exist, in the last successful match in the
1121 currently active dynamic scope.
1123 For example, C<$+{foo}> is equivalent to C<$1> after the following match:
1125 'foo' =~ /(?<foo>foo)/;
1127 The keys of the C<%+> hash list only the names of buffers that have
1128 captured (and that are thus associated to defined values).
1130 If multiple distinct capture groups have the same name, then
1131 C<$+{NAME}> will refer to the leftmost defined group in the match.
1133 The underlying behaviour of C<%+> is provided by the
1134 L<Tie::Hash::NamedCapture> module.
1136 B<Note:> C<%-> and C<%+> are tied views into a common internal hash
1137 associated with the last successful regular expression. Therefore mixing
1138 iterative access to them via C<each> may have unpredictable results.
1139 Likewise, if the last successful match changes, then the results may be
1142 This variable was added in Perl v5.10.0. The C<%{^CAPTURE}> alias was
1145 This variable is read-only and dynamically-scoped.
1147 =item @LAST_MATCH_START
1150 X<@-> X<@LAST_MATCH_START>
1152 C<$-[0]> is the offset of the start of the last successful match.
1153 C<$-[I<n>]> is the offset of the start of the substring matched by
1154 I<n>-th subpattern, or undef if the subpattern did not match.
1156 Thus, after a match against C<$_>, C<$&> coincides with C<substr $_, $-[0],
1157 $+[0] - $-[0]>. Similarly, $I<n> coincides with C<substr $_, $-[n],
1158 $+[n] - $-[n]> if C<$-[n]> is defined, and $+ coincides with
1159 C<substr $_, $-[$#-], $+[$#-] - $-[$#-]>. One can use C<$#-> to find the
1160 last matched subgroup in the last successful match. Contrast with
1161 C<$#+>, the number of subgroups in the regular expression. Compare
1164 This array holds the offsets of the beginnings of the last
1165 successful submatches in the currently active dynamic scope.
1166 C<$-[0]> is the offset into the string of the beginning of the
1167 entire match. The I<n>th element of this array holds the offset
1168 of the I<n>th submatch, so C<$-[1]> is the offset where C<$1>
1169 begins, C<$-[2]> the offset where C<$2> begins, and so on.
1171 After a match against some variable C<$var>:
1175 =item C<$`> is the same as C<substr($var, 0, $-[0])>
1177 =item C<$&> is the same as C<substr($var, $-[0], $+[0] - $-[0])>
1179 =item C<$'> is the same as C<substr($var, $+[0])>
1181 =item C<$1> is the same as C<substr($var, $-[1], $+[1] - $-[1])>
1183 =item C<$2> is the same as C<substr($var, $-[2], $+[2] - $-[2])>
1185 =item C<$3> is the same as C<substr($var, $-[3], $+[3] - $-[3])>
1189 This variable was added in Perl v5.6.0.
1191 =item %{^CAPTURE_ALL}
1197 Similar to C<%+>, this variable allows access to the named capture groups
1198 in the last successful match in the currently active dynamic scope. To
1199 each capture group name found in the regular expression, it associates a
1200 reference to an array containing the list of values captured by all
1201 buffers with that name (should there be several of them), in the order
1206 if ('1234' =~ /(?<A>1)(?<B>2)(?<A>3)(?<B>4)/) {
1207 foreach my $bufname (sort keys %-) {
1208 my $ary = $-{$bufname};
1209 foreach my $idx (0..$#$ary) {
1210 print "\$-{$bufname}[$idx] : ",
1211 (defined($ary->[$idx])
1226 The keys of the C<%-> hash correspond to all buffer names found in
1227 the regular expression.
1229 The behaviour of C<%-> is implemented via the
1230 L<Tie::Hash::NamedCapture> module.
1232 B<Note:> C<%-> and C<%+> are tied views into a common internal hash
1233 associated with the last successful regular expression. Therefore mixing
1234 iterative access to them via C<each> may have unpredictable results.
1235 Likewise, if the last successful match changes, then the results may be
1238 This variable was added in Perl v5.10.0. The C<%{^CAPTURE_ALL}> alias was
1241 This variable is read-only and dynamically-scoped.
1243 =item $LAST_REGEXP_CODE_RESULT
1246 X<$^R> X<$LAST_REGEXP_CODE_RESULT>
1248 The result of evaluation of the last successful C<(?{ code })>
1249 regular expression assertion (see L<perlre>). May be written to.
1251 This variable was added in Perl 5.005.
1253 =item ${^RE_COMPILE_RECURSION_LIMIT}
1254 X<${^RE_COMPILE_RECURSION_LIMIT}>
1256 The current value giving the maximum number of open but unclosed
1257 parenthetical groups there may be at any point during a regular
1258 expression compilation. The default is currently 1000 nested groups.
1259 You may adjust it depending on your needs and the amount of memory
1262 This variable was added in Perl v5.30.0.
1264 =item ${^RE_DEBUG_FLAGS}
1265 X<${^RE_DEBUG_FLAGS}>
1267 The current value of the regex debugging flags. Set to 0 for no debug output
1268 even when the C<re 'debug'> module is loaded. See L<re> for details.
1270 This variable was added in Perl v5.10.0.
1272 =item ${^RE_TRIE_MAXBUF}
1273 X<${^RE_TRIE_MAXBUF}>
1275 Controls how certain regex optimisations are applied and how much memory they
1276 utilize. This value by default is 65536 which corresponds to a 512kB
1277 temporary cache. Set this to a higher value to trade
1278 memory for speed when matching large alternations. Set
1279 it to a lower value if you want the optimisations to
1280 be as conservative of memory as possible but still occur, and set it to a
1281 negative value to prevent the optimisation and conserve the most memory.
1282 Under normal situations this variable should be of no interest to you.
1284 This variable was added in Perl v5.10.0.
1288 =head2 Variables related to filehandles
1290 Variables that depend on the currently selected filehandle may be set
1291 by calling an appropriate object method on the C<IO::Handle> object,
1292 although this is less efficient than using the regular built-in
1293 variables. (Summary lines below for this contain the word HANDLE.)
1298 after which you may use either
1304 HANDLE->method(EXPR)
1306 Each method returns the old value of the C<IO::Handle> attribute. The
1307 methods each take an optional EXPR, which, if supplied, specifies the
1308 new value for the C<IO::Handle> attribute in question. If not
1309 supplied, most methods do nothing to the current value--except for
1310 C<autoflush()>, which will assume a 1 for you, just to be different.
1312 Because loading in the C<IO::Handle> class is an expensive operation,
1313 you should learn how to use the regular built-in variables.
1315 A few of these variables are considered "read-only". This means that
1316 if you try to assign to this variable, either directly or indirectly
1317 through a reference, you'll raise a run-time exception.
1319 You should be very careful when modifying the default values of most
1320 special variables described in this document. In most cases you want
1321 to localize these variables before changing them, since if you don't,
1322 the change may affect other modules which rely on the default values
1323 of the special variables that you have changed. This is one of the
1324 correct ways to read the whole file at once:
1326 open my $fh, "<", "foo" or die $!;
1327 local $/; # enable localized slurp mode
1328 my $content = <$fh>;
1331 But the following code is quite bad:
1333 open my $fh, "<", "foo" or die $!;
1334 undef $/; # enable slurp mode
1335 my $content = <$fh>;
1338 since some other module, may want to read data from some file in the
1339 default "line mode", so if the code we have just presented has been
1340 executed, the global value of C<$/> is now changed for any other code
1341 running inside the same Perl interpreter.
1343 Usually when a variable is localized you want to make sure that this
1344 change affects the shortest scope possible. So unless you are already
1345 inside some short C<{}> block, you should create one yourself. For
1349 open my $fh, "<", "foo" or die $!;
1356 Here is an example of how your own code can go broken:
1366 # do something with $_
1369 You probably expect this code to print the equivalent of
1373 but instead you get:
1377 Why? Because C<nasty_break()> modifies C<$\> without localizing it
1378 first. The value you set in C<nasty_break()> is still there when you
1379 return. The fix is to add C<local()> so the value doesn't leak out of
1384 It's easy to notice the problem in such a short example, but in more
1385 complicated code you are looking for trouble if you don't localize
1386 changes to the special variables.
1393 Contains the name of the current file when reading from C<< <> >>.
1398 The array C<@ARGV> contains the command-line arguments intended for
1399 the script. C<$#ARGV> is generally the number of arguments minus
1400 one, because C<$ARGV[0]> is the first argument, I<not> the program's
1401 command name itself. See L</$0> for the command name.
1406 The special filehandle that iterates over command-line filenames in
1407 C<@ARGV>. Usually written as the null filehandle in the angle operator
1408 C<< <> >>. Note that currently C<ARGV> only has its magical effect
1409 within the C<< <> >> operator; elsewhere it is just a plain filehandle
1410 corresponding to the last file opened by C<< <> >>. In particular,
1411 passing C<\*ARGV> as a parameter to a function that expects a filehandle
1412 may not cause your function to automatically read the contents of all the
1418 The special filehandle that points to the currently open output file
1419 when doing edit-in-place processing with B<-i>. Useful when you have
1420 to do a lot of inserting and don't want to keep modifying C<$_>. See
1421 L<perlrun> for the B<-i> switch.
1423 =item IO::Handle->output_field_separator( EXPR )
1425 =item $OUTPUT_FIELD_SEPARATOR
1430 X<$,> X<$OFS> X<$OUTPUT_FIELD_SEPARATOR>
1432 The output field separator for the print operator. If defined, this
1433 value is printed between each of print's arguments. Default is C<undef>.
1435 You cannot call C<output_field_separator()> on a handle, only as a
1436 static method. See L<IO::Handle|IO::Handle>.
1438 Mnemonic: what is printed when there is a "," in your print statement.
1440 =item HANDLE->input_line_number( EXPR )
1442 =item $INPUT_LINE_NUMBER
1447 X<$.> X<$NR> X<$INPUT_LINE_NUMBER> X<line number>
1449 Current line number for the last filehandle accessed.
1451 Each filehandle in Perl counts the number of lines that have been read
1452 from it. (Depending on the value of C<$/>, Perl's idea of what
1453 constitutes a line may not match yours.) When a line is read from a
1454 filehandle (via C<readline()> or C<< <> >>), or when C<tell()> or
1455 C<seek()> is called on it, C<$.> becomes an alias to the line counter
1456 for that filehandle.
1458 You can adjust the counter by assigning to C<$.>, but this will not
1459 actually move the seek pointer. I<Localizing C<$.> will not localize
1460 the filehandle's line count>. Instead, it will localize perl's notion
1461 of which filehandle C<$.> is currently aliased to.
1463 C<$.> is reset when the filehandle is closed, but B<not> when an open
1464 filehandle is reopened without an intervening C<close()>. For more
1465 details, see L<perlop/"IE<sol>O Operators">. Because C<< <> >> never does
1466 an explicit close, line numbers increase across C<ARGV> files (but see
1467 examples in L<perlfunc/eof>).
1469 You can also use C<< HANDLE->input_line_number(EXPR) >> to access the
1470 line counter for a given filehandle without having to worry about
1471 which handle you last accessed.
1473 Mnemonic: many programs use "." to mean the current line number.
1475 =item IO::Handle->input_record_separator( EXPR )
1477 =item $INPUT_RECORD_SEPARATOR
1482 X<$/> X<$RS> X<$INPUT_RECORD_SEPARATOR>
1484 The input record separator, newline by default. This influences Perl's
1485 idea of what a "line" is. Works like B<awk>'s RS variable, including
1486 treating empty lines as a terminator if set to the null string (an
1487 empty line cannot contain any spaces or tabs). You may set it to a
1488 multi-character string to match a multi-character terminator, or to
1489 C<undef> to read through the end of file. Setting it to C<"\n\n">
1490 means something slightly different than setting to C<"">, if the file
1491 contains consecutive empty lines. Setting to C<""> will treat two or
1492 more consecutive empty lines as a single empty line. Setting to
1493 C<"\n\n"> will blindly assume that the next input character belongs to
1494 the next paragraph, even if it's a newline.
1496 local $/; # enable "slurp" mode
1497 local $_ = <FH>; # whole file now here
1500 Remember: the value of C<$/> is a string, not a regex. B<awk> has to
1501 be better for something. :-)
1503 Setting C<$/> to an empty string -- the so-called I<paragraph mode> -- merits
1504 special attention. When C<$/> is set to C<""> and the entire file is read in
1505 with that setting, any sequence of consecutive newlines C<"\n\n"> at the
1506 beginning of the file is discarded. With the exception of the final record in
1507 the file, each sequence of characters ending in two or more newlines is
1508 treated as one record and is read in to end in exactly two newlines. If the
1509 last record in the file ends in zero or one consecutive newlines, that record
1510 is read in with that number of newlines. If the last record ends in two or
1511 more consecutive newlines, it is read in with two newlines like all preceding
1514 Suppose we wrote the following string to a file:
1516 my $string = "\n\n\n";
1517 $string .= "alpha beta\ngamma delta\n\n\n";
1518 $string .= "epsilon zeta eta\n\n";
1519 $string .= "theta\n";
1521 my $file = 'simple_file.txt';
1522 open my $OUT, '>', $file or die;
1526 Now we read that file in paragraph mode:
1528 local $/ = ""; # paragraph mode
1529 open my $IN, '<', $file or die;
1530 my @records = <$IN>;
1533 C<@records> will consist of these 3 strings:
1536 "alpha beta\ngamma delta\n\n",
1537 "epsilon zeta eta\n\n",
1541 Setting C<$/> to a reference to an integer, scalar containing an
1542 integer, or scalar that's convertible to an integer will attempt to
1543 read records instead of lines, with the maximum record size being the
1544 referenced integer number of characters. So this:
1546 local $/ = \32768; # or \"32768", or \$var_containing_32768
1547 open my $fh, "<", $myfile or die $!;
1550 will read a record of no more than 32768 characters from $fh. If you're
1551 not reading from a record-oriented file (or your OS doesn't have
1552 record-oriented files), then you'll likely get a full chunk of data
1553 with every read. If a record is larger than the record size you've
1554 set, you'll get the record back in pieces. Trying to set the record
1555 size to zero or less is deprecated and will cause $/ to have the value
1556 of "undef", which will cause reading in the (rest of the) whole file.
1558 As of 5.19.9 setting C<$/> to any other form of reference will throw a
1559 fatal exception. This is in preparation for supporting new ways to set
1560 C<$/> in the future.
1562 On VMS only, record reads bypass PerlIO layers and any associated
1563 buffering, so you must not mix record and non-record reads on the
1564 same filehandle. Record mode mixes with line mode only when the
1565 same buffering layer is in use for both modes.
1567 You cannot call C<input_record_separator()> on a handle, only as a
1568 static method. See L<IO::Handle|IO::Handle>.
1570 See also L<perlport/"Newlines">. Also see L</$.>.
1572 Mnemonic: / delimits line boundaries when quoting poetry.
1574 =item IO::Handle->output_record_separator( EXPR )
1576 =item $OUTPUT_RECORD_SEPARATOR
1581 X<$\> X<$ORS> X<$OUTPUT_RECORD_SEPARATOR>
1583 The output record separator for the print operator. If defined, this
1584 value is printed after the last of print's arguments. Default is C<undef>.
1586 You cannot call C<output_record_separator()> on a handle, only as a
1587 static method. See L<IO::Handle|IO::Handle>.
1589 Mnemonic: you set C<$\> instead of adding "\n" at the end of the print.
1590 Also, it's just like C<$/>, but it's what you get "back" from Perl.
1592 =item HANDLE->autoflush( EXPR )
1594 =item $OUTPUT_AUTOFLUSH
1597 X<$|> X<autoflush> X<flush> X<$OUTPUT_AUTOFLUSH>
1599 If set to nonzero, forces a flush right away and after every write or
1600 print on the currently selected output channel. Default is 0
1601 (regardless of whether the channel is really buffered by the system or
1602 not; C<$|> tells you only whether you've asked Perl explicitly to
1603 flush after each write). STDOUT will typically be line buffered if
1604 output is to the terminal and block buffered otherwise. Setting this
1605 variable is useful primarily when you are outputting to a pipe or
1606 socket, such as when you are running a Perl program under B<rsh> and
1607 want to see the output as it's happening. This has no effect on input
1608 buffering. See L<perlfunc/getc> for that. See L<perlfunc/select> on
1609 how to select the output channel. See also L<IO::Handle>.
1611 Mnemonic: when you want your pipes to be piping hot.
1616 This read-only variable contains a reference to the last-read filehandle.
1617 This is set by C<< <HANDLE> >>, C<readline>, C<tell>, C<eof> and C<seek>.
1618 This is the same handle that C<$.> and C<tell> and C<eof> without arguments
1619 use. It is also the handle used when Perl appends ", <STDIN> line 1" to
1620 an error or warning message.
1622 This variable was added in Perl v5.18.0.
1626 =head3 Variables related to formats
1628 The special variables for formats are a subset of those for
1629 filehandles. See L<perlform> for more information about Perl's
1637 X<$^A> X<$ACCUMULATOR>
1639 The current value of the C<write()> accumulator for C<format()> lines.
1640 A format contains C<formline()> calls that put their result into
1641 C<$^A>. After calling its format, C<write()> prints out the contents
1642 of C<$^A> and empties. So you never really see the contents of C<$^A>
1643 unless you call C<formline()> yourself and then look at it. See
1644 L<perlform> and L<perlfunc/"formline PICTURE,LIST">.
1646 =item IO::Handle->format_formfeed(EXPR)
1648 =item $FORMAT_FORMFEED
1651 X<$^L> X<$FORMAT_FORMFEED>
1653 What formats output as a form feed. The default is C<\f>.
1655 You cannot call C<format_formfeed()> on a handle, only as a static
1656 method. See L<IO::Handle|IO::Handle>.
1658 =item HANDLE->format_page_number(EXPR)
1660 =item $FORMAT_PAGE_NUMBER
1663 X<$%> X<$FORMAT_PAGE_NUMBER>
1665 The current page number of the currently selected output channel.
1667 Mnemonic: C<%> is page number in B<nroff>.
1669 =item HANDLE->format_lines_left(EXPR)
1671 =item $FORMAT_LINES_LEFT
1674 X<$-> X<$FORMAT_LINES_LEFT>
1676 The number of lines left on the page of the currently selected output
1679 Mnemonic: lines_on_page - lines_printed.
1681 =item IO::Handle->format_line_break_characters EXPR
1683 =item $FORMAT_LINE_BREAK_CHARACTERS
1686 X<$:> X<FORMAT_LINE_BREAK_CHARACTERS>
1688 The current set of characters after which a string may be broken to
1689 fill continuation fields (starting with C<^>) in a format. The default is
1690 S<" \n-">, to break on a space, newline, or a hyphen.
1692 You cannot call C<format_line_break_characters()> on a handle, only as
1693 a static method. See L<IO::Handle|IO::Handle>.
1695 Mnemonic: a "colon" in poetry is a part of a line.
1697 =item HANDLE->format_lines_per_page(EXPR)
1699 =item $FORMAT_LINES_PER_PAGE
1702 X<$=> X<$FORMAT_LINES_PER_PAGE>
1704 The current page length (printable lines) of the currently selected
1705 output channel. The default is 60.
1707 Mnemonic: = has horizontal lines.
1709 =item HANDLE->format_top_name(EXPR)
1711 =item $FORMAT_TOP_NAME
1714 X<$^> X<$FORMAT_TOP_NAME>
1716 The name of the current top-of-page format for the currently selected
1717 output channel. The default is the name of the filehandle with C<_TOP>
1718 appended. For example, the default format top name for the C<STDOUT>
1719 filehandle is C<STDOUT_TOP>.
1721 Mnemonic: points to top of page.
1723 =item HANDLE->format_name(EXPR)
1728 X<$~> X<$FORMAT_NAME>
1730 The name of the current report format for the currently selected
1731 output channel. The default format name is the same as the filehandle
1732 name. For example, the default format name for the C<STDOUT>
1733 filehandle is just C<STDOUT>.
1735 Mnemonic: brother to C<$^>.
1739 =head2 Error Variables
1740 X<error> X<exception>
1742 The variables C<$@>, C<$!>, C<$^E>, and C<$?> contain information
1743 about different types of error conditions that may appear during
1744 execution of a Perl program. The variables are shown ordered by
1745 the "distance" between the subsystem which reported the error and
1746 the Perl process. They correspond to errors detected by the Perl
1747 interpreter, C library, operating system, or an external program,
1750 To illustrate the differences between these variables, consider the
1751 following Perl expression, which uses a single-quoted string. After
1752 execution of this statement, perl may have set all four special error
1756 open my $pipe, "/cdrom/install |" or die $!;
1758 close $pipe or die "bad pipe: $?, $!";
1761 When perl executes the C<eval()> expression, it translates the
1762 C<open()>, C<< <PIPE> >>, and C<close> calls in the C run-time library
1763 and thence to the operating system kernel. perl sets C<$!> to
1764 the C library's C<errno> if one of these calls fails.
1766 C<$@> is set if the string to be C<eval>-ed did not compile (this may
1767 happen if C<open> or C<close> were imported with bad prototypes), or
1768 if Perl code executed during evaluation C<die()>d. In these cases the
1769 value of C<$@> is the compile error, or the argument to C<die> (which
1770 will interpolate C<$!> and C<$?>). (See also L<Fatal>, though.)
1772 Under a few operating systems, C<$^E> may contain a more verbose error
1773 indicator, such as in this case, "CDROM tray not closed." Systems that
1774 do not support extended error messages leave C<$^E> the same as C<$!>.
1776 Finally, C<$?> may be set to a non-0 value if the external program
1777 F</cdrom/install> fails. The upper eight bits reflect specific error
1778 conditions encountered by the program (the program's C<exit()> value).
1779 The lower eight bits reflect mode of failure, like signal death and
1780 core dump information. See L<wait(2)> for details. In contrast to
1781 C<$!> and C<$^E>, which are set only if an error condition is detected,
1782 the variable C<$?> is set on each C<wait> or pipe C<close>,
1783 overwriting the old value. This is more like C<$@>, which on every
1784 C<eval()> is always set on failure and cleared on success.
1786 For more details, see the individual descriptions at C<$@>, C<$!>,
1791 =item ${^CHILD_ERROR_NATIVE}
1792 X<$^CHILD_ERROR_NATIVE>
1794 The native status returned by the last pipe close, backtick (C<``>)
1795 command, successful call to C<wait()> or C<waitpid()>, or from the
1796 C<system()> operator. On POSIX-like systems this value can be decoded
1797 with the WIFEXITED, WEXITSTATUS, WIFSIGNALED, WTERMSIG, WIFSTOPPED,
1798 WSTOPSIG and WIFCONTINUED functions provided by the L<POSIX> module.
1800 Under VMS this reflects the actual VMS exit status; i.e. it is the
1801 same as C<$?> when the pragma C<use vmsish 'status'> is in effect.
1803 This variable was added in Perl v5.10.0.
1805 =item $EXTENDED_OS_ERROR
1808 X<$^E> X<$EXTENDED_OS_ERROR>
1810 Error information specific to the current operating system. At the
1811 moment, this differs from C<L</$!>> under only VMS, OS/2, and Win32 (and
1812 for MacPerl). On all other platforms, C<$^E> is always just the same
1815 Under VMS, C<$^E> provides the VMS status value from the last system
1816 error. This is more specific information about the last system error
1817 than that provided by C<$!>. This is particularly important when C<$!>
1818 is set to B<EVMSERR>.
1820 Under OS/2, C<$^E> is set to the error code of the last call to OS/2
1821 API either via CRT, or directly from perl.
1823 Under Win32, C<$^E> always returns the last error information reported
1824 by the Win32 call C<GetLastError()> which describes the last error
1825 from within the Win32 API. Most Win32-specific code will report errors
1826 via C<$^E>. ANSI C and Unix-like calls set C<errno> and so most
1827 portable Perl code will report errors via C<$!>.
1829 Caveats mentioned in the description of C<L</$!>> generally apply to
1832 This variable was added in Perl 5.003.
1834 Mnemonic: Extra error explanation.
1836 =item $EXCEPTIONS_BEING_CAUGHT
1839 X<$^S> X<$EXCEPTIONS_BEING_CAUGHT>
1841 Current state of the interpreter.
1844 --------- -------------------------------------
1845 undef Parsing module, eval, or main program
1846 true (1) Executing an eval
1849 The first state may happen in C<$SIG{__DIE__}> and C<$SIG{__WARN__}>
1852 The English name $EXCEPTIONS_BEING_CAUGHT is slightly misleading, because
1853 the C<undef> value does not indicate whether exceptions are being caught,
1854 since compilation of the main program does not catch exceptions.
1856 This variable was added in Perl 5.004.
1863 The current value of the warning switch, initially true if B<-w> was
1864 used, false otherwise, but directly modifiable.
1866 See also L<warnings>.
1868 Mnemonic: related to the B<-w> switch.
1870 =item ${^WARNING_BITS}
1873 The current set of warning checks enabled by the C<use warnings> pragma.
1874 It has the same scoping as the C<$^H> and C<%^H> variables. The exact
1875 values are considered internal to the L<warnings> pragma and may change
1876 between versions of Perl.
1878 This variable was added in Perl v5.6.0.
1885 X<$!> X<$ERRNO> X<$OS_ERROR>
1887 When referenced, C<$!> retrieves the current value
1888 of the C C<errno> integer variable.
1889 If C<$!> is assigned a numerical value, that value is stored in C<errno>.
1890 When referenced as a string, C<$!> yields the system error string
1891 corresponding to C<errno>.
1893 Many system or library calls set C<errno> if they fail,
1894 to indicate the cause of failure. They usually do B<not>
1895 set C<errno> to zero if they succeed. This means C<errno>,
1896 hence C<$!>, is meaningful only I<immediately> after a B<failure>:
1898 if (open my $fh, "<", $filename) {
1899 # Here $! is meaningless.
1903 # ONLY here is $! meaningful.
1905 # Already here $! might be meaningless.
1907 # Since here we might have either success or failure,
1908 # $! is meaningless.
1910 Here, I<meaningless> means that C<$!> may be unrelated to the outcome
1911 of the C<open()> operator. Assignment to C<$!> is similarly ephemeral.
1912 It can be used immediately before invoking the C<die()> operator,
1913 to set the exit value, or to inspect the system error string
1914 corresponding to error I<n>, or to restore C<$!> to a meaningful state.
1916 Mnemonic: What just went bang?
1923 X<%!> X<%OS_ERROR> X<%ERRNO>
1925 Each element of C<%!> has a true value only if C<$!> is set to that
1926 value. For example, C<$!{ENOENT}> is true if and only if the current
1927 value of C<$!> is C<ENOENT>; that is, if the most recent error was "No
1928 such file or directory" (or its moral equivalent: not all operating
1929 systems give that exact error, and certainly not all languages). The
1930 specific true value is not guaranteed, but in the past has generally
1931 been the numeric value of C<$!>. To check if a particular key is
1932 meaningful on your system, use C<exists $!{the_key}>; for a list of legal
1933 keys, use C<keys %!>. See L<Errno> for more information, and also see
1936 This variable was added in Perl 5.005.
1941 X<$?> X<$CHILD_ERROR>
1943 The status returned by the last pipe close, backtick (C<``>) command,
1944 successful call to C<wait()> or C<waitpid()>, or from the C<system()>
1945 operator. This is just the 16-bit status word returned by the
1946 traditional Unix C<wait()> system call (or else is made up to look
1947 like it). Thus, the exit value of the subprocess is really (C<<< $? >>
1948 8 >>>), and C<$? & 127> gives which signal, if any, the process died
1949 from, and C<$? & 128> reports whether there was a core dump.
1951 Additionally, if the C<h_errno> variable is supported in C, its value
1952 is returned via C<$?> if any C<gethost*()> function fails.
1954 If you have installed a signal handler for C<SIGCHLD>, the
1955 value of C<$?> will usually be wrong outside that handler.
1957 Inside an C<END> subroutine C<$?> contains the value that is going to be
1958 given to C<exit()>. You can modify C<$?> in an C<END> subroutine to
1959 change the exit status of your program. For example:
1962 $? = 1 if $? == 255; # die would make it 255
1965 Under VMS, the pragma C<use vmsish 'status'> makes C<$?> reflect the
1966 actual VMS exit status, instead of the default emulation of POSIX
1967 status; see L<perlvms/$?> for details.
1969 Mnemonic: similar to B<sh> and B<ksh>.
1974 X<$@> X<$EVAL_ERROR>
1976 The Perl error from the last C<eval> operator, i.e. the last exception that
1977 was caught. For C<eval BLOCK>, this is either a runtime error message or the
1978 string or reference C<die> was called with. The C<eval STRING> form also
1979 catches syntax errors and other compile time exceptions.
1981 If no error occurs, C<eval> sets C<$@> to the empty string.
1983 Warning messages are not collected in this variable. You can, however,
1984 set up a routine to process warnings by setting C<$SIG{__WARN__}> as
1985 described in L</%SIG>.
1987 Mnemonic: Where was the error "at"?
1991 =head2 Variables related to the interpreter state
1993 These variables provide information about the current interpreter state.
2000 X<$^C> X<$COMPILING>
2002 The current value of the flag associated with the B<-c> switch.
2003 Mainly of use with B<-MO=...> to allow code to alter its behavior
2004 when being compiled, such as for example to C<AUTOLOAD> at compile
2005 time rather than normal, deferred loading. Setting
2006 C<$^C = 1> is similar to calling C<B::minus_c>.
2008 This variable was added in Perl v5.6.0.
2013 X<$^D> X<$DEBUGGING>
2015 The current value of the debugging flags. May be read or set. Like its
2016 L<command-line equivalent|perlrun/B<-D>I<letters>>, you can use numeric
2017 or symbolic values, e.g. C<$^D = 10> or C<$^D = "st">. See
2018 L<perlrun/B<-D>I<number>>. The contents of this variable also affects the
2019 debugger operation. See L<perldebguts/Debugger Internals>.
2021 Mnemonic: value of B<-D> switch.
2026 This variable is no longer supported.
2028 It used to hold the I<object reference> to the C<Encode> object that was
2029 used to convert the source code to Unicode.
2031 Its purpose was to allow your non-ASCII Perl
2032 scripts not to have to be written in UTF-8; this was
2033 useful before editors that worked on UTF-8 encoded text were common, but
2034 that was long ago. It caused problems, such as affecting the operation
2035 of other modules that weren't expecting it, causing general mayhem.
2037 If you need something like this functionality, it is recommended that use
2038 you a simple source filter, such as L<Filter::Encoding>.
2040 If you are coming here because code of yours is being adversely affected
2041 by someone's use of this variable, you can usually work around it by
2046 near the beginning of the functions that are getting broken. This
2047 undefines the variable during the scope of execution of the including
2050 This variable was added in Perl 5.8.2 and removed in 5.26.0.
2051 Setting it to anything other than C<undef> was made fatal in Perl 5.28.0.
2053 =item ${^GLOBAL_PHASE}
2056 The current phase of the perl interpreter.
2058 Possible values are:
2064 The C<PerlInterpreter*> is being constructed via C<perl_construct>. This
2065 value is mostly there for completeness and for use via the
2066 underlying C variable C<PL_phase>. It's not really possible for Perl
2067 code to be executed unless construction of the interpreter is
2072 This is the global compile-time. That includes, basically, every
2073 C<BEGIN> block executed directly or indirectly from during the
2074 compile-time of the top-level program.
2076 This phase is not called "BEGIN" to avoid confusion with
2077 C<BEGIN>-blocks, as those are executed during compile-time of any
2078 compilation unit, not just the top-level program. A new, localised
2079 compile-time entered at run-time, for example by constructs as
2080 C<eval "use SomeModule"> are not global interpreter phases, and
2081 therefore aren't reflected by C<${^GLOBAL_PHASE}>.
2085 Execution of any C<CHECK> blocks.
2089 Similar to "CHECK", but for C<INIT>-blocks, not C<CHECK> blocks.
2093 The main run-time, i.e. the execution of C<PL_main_root>.
2097 Execution of any C<END> blocks.
2105 Also note that there's no value for UNITCHECK-blocks. That's because
2106 those are run for each compilation unit individually, and therefore is
2107 not a global interpreter phase.
2109 Not every program has to go through each of the possible phases, but
2110 transition from one phase to another can only happen in the order
2111 described in the above list.
2113 An example of all of the phases Perl code can see:
2115 BEGIN { print "compile-time: ${^GLOBAL_PHASE}\n" }
2117 INIT { print "init-time: ${^GLOBAL_PHASE}\n" }
2119 CHECK { print "check-time: ${^GLOBAL_PHASE}\n" }
2122 package Print::Phase;
2125 my ($class, $time) = @_;
2126 return bless \$time, $class;
2131 print "$$self: ${^GLOBAL_PHASE}\n";
2135 print "run-time: ${^GLOBAL_PHASE}\n";
2137 my $runtime = Print::Phase->new(
2138 "lexical variables are garbage collected before END"
2141 END { print "end-time: ${^GLOBAL_PHASE}\n" }
2143 our $destruct = Print::Phase->new(
2144 "package variables are garbage collected after END"
2153 lexical variables are garbage collected before END: RUN
2155 package variables are garbage collected after END: DESTRUCT
2157 This variable was added in Perl 5.14.0.
2162 WARNING: This variable is strictly for
2163 internal use only. Its availability,
2164 behavior, and contents are subject to change without notice.
2166 This variable contains compile-time hints for the Perl interpreter. At the
2167 end of compilation of a BLOCK the value of this variable is restored to the
2168 value when the interpreter started to compile the BLOCK.
2170 When perl begins to parse any block construct that provides a lexical scope
2171 (e.g., eval body, required file, subroutine body, loop body, or conditional
2172 block), the existing value of C<$^H> is saved, but its value is left unchanged.
2173 When the compilation of the block is completed, it regains the saved value.
2174 Between the points where its value is saved and restored, code that
2175 executes within BEGIN blocks is free to change the value of C<$^H>.
2177 This behavior provides the semantic of lexical scoping, and is used in,
2178 for instance, the C<use strict> pragma.
2180 The contents should be an integer; different bits of it are used for
2181 different pragmatic flags. Here's an example:
2183 sub add_100 { $^H |= 0x100 }
2190 Consider what happens during execution of the BEGIN block. At this point
2191 the BEGIN block has already been compiled, but the body of C<foo()> is still
2192 being compiled. The new value of C<$^H>
2193 will therefore be visible only while
2194 the body of C<foo()> is being compiled.
2196 Substitution of C<BEGIN { add_100() }> block with:
2198 BEGIN { require strict; strict->import('vars') }
2200 demonstrates how C<use strict 'vars'> is implemented. Here's a conditional
2201 version of the same lexical pragma:
2204 require strict; strict->import('vars') if $condition
2207 This variable was added in Perl 5.003.
2212 The C<%^H> hash provides the same scoping semantic as C<$^H>. This makes
2213 it useful for implementation of lexically scoped pragmas. See
2214 L<perlpragma>. All the entries are stringified when accessed at
2215 runtime, so only simple values can be accommodated. This means no
2216 pointers to objects, for example.
2218 When putting items into C<%^H>, in order to avoid conflicting with other
2219 users of the hash there is a convention regarding which keys to use.
2220 A module should use only keys that begin with the module's name (the
2221 name of its main package) and a "/" character. For example, a module
2222 C<Foo::Bar> should use keys such as C<Foo::Bar/baz>.
2224 This variable was added in Perl v5.6.0.
2229 An internal variable used by PerlIO. A string in two parts, separated
2230 by a C<\0> byte, the first part describes the input layers, the second
2231 part describes the output layers.
2233 This variable was added in Perl v5.8.0.
2240 The internal variable for debugging support. The meanings of the
2241 various bits are subject to change, but currently indicate:
2247 Debug subroutine enter/exit.
2251 Line-by-line debugging. Causes C<DB::DB()> subroutine to be called for
2252 each statement executed. Also causes saving source code lines (like
2257 Switch off optimizations.
2261 Preserve more data for future interactive inspections.
2265 Keep info about source lines on which a subroutine is defined.
2269 Start with single-step on.
2273 Use subroutine address instead of name when reporting.
2277 Report C<goto &subroutine> as well.
2281 Provide informative "file" names for evals based on the place they were compiled.
2285 Provide informative names to anonymous subroutines based on the place they
2290 Save source code lines into C<@{"_<$filename"}>.
2294 When saving source, include evals that generate no subroutines.
2298 When saving source, include source that did not compile.
2302 Some bits may be relevant at compile-time only, some at
2303 run-time only. This is a new mechanism and the details may change.
2304 See also L<perldebguts>.
2309 Reflects if taint mode is on or off. 1 for on (the program was run with
2310 B<-T>), 0 for off, -1 when only taint warnings are enabled (i.e. with
2313 This variable is read-only.
2315 This variable was added in Perl v5.8.0.
2317 =item ${^SAFE_LOCALES}
2320 Reflects if safe locale operations are available to this perl (when the
2321 value is 1) or not (the value is 0). This variable is always 1 if the
2322 perl has been compiled without threads. It is also 1 if this perl is
2323 using thread-safe locale operations. Note that an individual thread may
2324 choose to use the global locale (generally unsafe) by calling
2325 L<perlapi/switch_to_global_locale>. This variable currently is still
2326 set to 1 in such threads.
2328 This variable is read-only.
2330 This variable was added in Perl v5.28.0.
2335 Reflects certain Unicode settings of Perl. See L<perlrun>
2336 documentation for the C<-C> switch for more information about
2337 the possible values.
2339 This variable is set during Perl startup and is thereafter read-only.
2341 This variable was added in Perl v5.8.2.
2346 This variable controls the state of the internal UTF-8 offset caching code.
2347 1 for on (the default), 0 for off, -1 to debug the caching code by checking
2348 all its results against linear scans, and panicking on any discrepancy.
2350 This variable was added in Perl v5.8.9. It is subject to change or
2351 removal without notice, but is currently used to avoid recalculating the
2352 boundaries of multi-byte UTF-8-encoded characters.
2354 =item ${^UTF8LOCALE}
2357 This variable indicates whether a UTF-8 locale was detected by perl at
2358 startup. This information is used by perl when it's in
2359 adjust-utf8ness-to-locale mode (as when run with the C<-CL> command-line
2360 switch); see L<perlrun> for more info on this.
2362 This variable was added in Perl v5.8.8.
2366 =head2 Deprecated and removed variables
2368 Deprecating a variable announces the intent of the perl maintainers to
2369 eventually remove the variable from the language. It may still be
2370 available despite its status. Using a deprecated variable triggers
2373 Once a variable is removed, its use triggers an error telling you
2374 the variable is unsupported.
2376 See L<perldiag> for details about error messages.
2383 C<$#> was a variable that could be used to format printed numbers.
2384 After a deprecation cycle, its magic was removed in Perl v5.10.0 and
2385 using it now triggers a warning: C<$# is no longer supported>.
2387 This is not the sigil you use in front of an array name to get the
2388 last index, like C<$#array>. That's still how you get the last index
2389 of an array in Perl. The two have nothing to do with each other.
2391 Deprecated in Perl 5.
2393 Removed in Perl v5.10.0.
2398 C<$*> was a variable that you could use to enable multiline matching.
2399 After a deprecation cycle, its magic was removed in Perl v5.10.0.
2400 Using it now triggers a warning: C<$* is no longer supported>.
2401 You should use the C</s> and C</m> regexp modifiers instead.
2403 Deprecated in Perl 5.
2405 Removed in Perl v5.10.0.
2410 This variable stores the index of the first element in an array, and
2411 of the first character in a substring. The default is 0, but you could
2412 theoretically set it to 1 to make Perl behave more like B<awk> (or Fortran)
2413 when subscripting and when evaluating the index() and substr() functions.
2415 As of release 5 of Perl, assignment to C<$[> is treated as a compiler
2416 directive, and cannot influence the behavior of any other file.
2417 (That's why you can only assign compile-time constants to it.)
2418 Its use is highly discouraged.
2420 Prior to Perl v5.10.0, assignment to C<$[> could be seen from outer lexical
2421 scopes in the same file, unlike other compile-time directives (such as
2422 L<strict>). Using local() on it would bind its value strictly to a lexical
2423 block. Now it is always lexically scoped.
2425 As of Perl v5.16.0, it is implemented by the L<arybase> module.
2427 As of Perl v5.30.0, or under C<use v5.16>, or C<no feature "array_base">,
2428 C<$[> no longer has any effect, and always contains 0.
2429 Assigning 0 to it is permitted, but any other value will produce an error.
2431 Mnemonic: [ begins subscripts.
2433 Deprecated in Perl v5.12.0.