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 "$]" < 5.008;
442 When comparing C<$]>, numeric comparison operators should be used, but the
443 variable should be stringified first to avoid issues where its original
444 numeric value is inaccurate.
446 See also the documentation of C<use VERSION> and C<require VERSION>
447 for a convenient way to fail if the running Perl interpreter is too old.
449 See L</$^V> for a representation of the Perl version as a L<version>
450 object, which allows more flexible string comparisons.
452 The main advantage of C<$]> over C<$^V> is that it works the same on any
453 version of Perl. The disadvantages are that it can't easily be compared
454 to versions in other formats (e.g. literal v-strings, "v1.2.3" or
455 version objects) and numeric comparisons are subject to the binary
456 floating point representation; it's good for numeric literal version
457 checks and bad for comparing to a variable that hasn't been
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
610 this special case. Using an empty string or C<undef> as the value has
611 the same effect as C<'DEFAULT'>.
613 Here are some other examples:
615 $SIG{"PIPE"} = "Plumber"; # assumes main::Plumber (not
617 $SIG{"PIPE"} = \&Plumber; # just fine; assume current
619 $SIG{"PIPE"} = *Plumber; # somewhat esoteric
620 $SIG{"PIPE"} = Plumber(); # oops, what did Plumber()
623 Be sure not to use a bareword as the name of a signal handler,
624 lest you inadvertently call it.
626 Using a string that doesn't correspond to any existing function or a
627 glob that doesn't contain a code slot is equivalent to C<'IGNORE'>,
628 but a warning is emitted when the handler is being called (the warning
629 is not emitted for the internal hooks described below).
631 If your system has the C<sigaction()> function then signal handlers
632 are installed using it. This means you get reliable signal handling.
634 The default delivery policy of signals changed in Perl v5.8.0 from
635 immediate (also known as "unsafe") to deferred, also known as "safe
636 signals". See L<perlipc> for more information.
638 Certain internal hooks can be also set using the C<%SIG> hash. The
639 routine indicated by C<$SIG{__WARN__}> is called when a warning
640 message is about to be printed. The warning message is passed as the
641 first argument. The presence of a C<__WARN__> hook causes the
642 ordinary printing of warnings to C<STDERR> to be suppressed. You can
643 use this to save warnings in a variable, or turn warnings into fatal
646 local $SIG{__WARN__} = sub { die $_[0] };
649 As the C<'IGNORE'> hook is not supported by C<__WARN__>, its effect is
650 the same as using C<'DEFAULT'>. You can disable warnings using the
653 local $SIG{__WARN__} = sub {};
655 The routine indicated by C<$SIG{__DIE__}> is called when a fatal
656 exception is about to be thrown. The error message is passed as the
657 first argument. When a C<__DIE__> hook routine returns, the exception
658 processing continues as it would have in the absence of the hook,
659 unless the hook routine itself exits via a C<goto &sub>, a loop exit,
660 or a C<die()>. The C<__DIE__> handler is explicitly disabled during
661 the call, so that you can die from a C<__DIE__> handler. Similarly
664 The C<$SIG{__DIE__}> hook is called even inside an C<eval()>. It was
665 never intended to happen this way, but an implementation glitch made
666 this possible. This used to be deprecated, as it allowed strange action
667 at a distance like rewriting a pending exception in C<$@>. Plans to
668 rectify this have been scrapped, as users found that rewriting a
669 pending exception is actually a useful feature, and not a bug.
671 The C<$SIG{__DIE__}> doesn't support C<'IGNORE'>; it has the same
672 effect as C<'DEFAULT'>.
674 C<__DIE__>/C<__WARN__> handlers are very special in one respect: they
675 may be called to report (probable) errors found by the parser. In such
676 a case the parser may be in inconsistent state, so any attempt to
677 evaluate Perl code from such a handler will probably result in a
678 segfault. This means that warnings or errors that result from parsing
679 Perl should be used with extreme caution, like this:
681 require Carp if defined $^S;
682 Carp::confess("Something wrong") if defined &Carp::confess;
683 die "Something wrong, but could not load Carp to give "
685 . "To see backtrace try starting Perl with -MCarp switch";
687 Here the first line will load C<Carp> I<unless> it is the parser who
688 called the handler. The second line will print backtrace and die if
689 C<Carp> was available. The third line will be executed only if C<Carp> was
692 Having to even think about the C<$^S> variable in your exception
693 handlers is simply wrong. C<$SIG{__DIE__}> as currently implemented
694 invites grievous and difficult to track down errors. Avoid it
695 and use an C<END{}> or CORE::GLOBAL::die override instead.
697 See L<perlfunc/die>, L<perlfunc/warn>, L<perlfunc/eval>, and
698 L<warnings> for additional information.
705 The time at which the program began running, in seconds since the
706 epoch (beginning of 1970). The values returned by the B<-M>, B<-A>,
707 and B<-C> filetests are based on this value.
712 X<$^V> X<$PERL_VERSION>
715 These are documented in the generated file lib/Config.pod. This looks
716 like as good a place as any to give notice that they are documented.
718 =for apidoc hAmn|int|PERL_VERSION
719 =for apidoc hAmn|int|PERL_REVISION
720 =for apidoc hAmn|int|PERL_SUBVERSION
722 The revision, version, and subversion of the Perl interpreter,
723 represented as a L<version> object.
725 This variable first appeared in perl v5.6.0; earlier versions of perl
726 will see an undefined value. Before perl v5.10.0 C<$^V> was represented
727 as a v-string rather than a L<version> object.
729 C<$^V> can be used to determine whether the Perl interpreter executing
730 a script is in the right range of versions. For example:
732 warn "Hashes not randomized!\n" if !$^V or $^V lt v5.8.1
734 While version objects overload stringification, to portably convert
735 C<$^V> into its string representation, use C<sprintf()>'s C<"%vd">
736 conversion, which works for both v-strings or version objects:
738 printf "version is v%vd\n", $^V; # Perl's version
740 See the documentation of C<use VERSION> and C<require VERSION>
741 for a convenient way to fail if the running Perl interpreter is too old.
743 See also C<L</$]>> for a decimal representation of the Perl version.
745 The main advantage of C<$^V> over C<$]> is that, for Perl v5.10.0 or
746 later, it overloads operators, allowing easy comparison against other
747 version representations (e.g. decimal, literal v-string, "v1.2.3", or
748 objects). The disadvantage is that prior to v5.10.0, it was only a
749 literal v-string, which can't be easily printed or compared, whereas
750 the behavior of C<$]> is unchanged on all versions of Perl.
752 Mnemonic: use ^V for a version object.
754 =item ${^WIN32_SLOPPY_STAT}
755 X<${^WIN32_SLOPPY_STAT}> X<sitecustomize> X<sitecustomize.pl>
757 If this variable is set to a true value, then C<stat()> on Windows will
758 not try to open the file. This means that the link count cannot be
759 determined and file attributes may be out of date if additional
760 hardlinks to the file exist. On the other hand, not opening the file
761 is considerably faster, especially for files on network drives.
763 This variable could be set in the F<sitecustomize.pl> file to
764 configure the local Perl installation to use "sloppy" C<stat()> by
765 default. See the documentation for B<-f> in
766 L<perlrun|perlrun/"Command Switches"> for more information about site
769 This variable was added in Perl v5.10.0.
771 =item $EXECUTABLE_NAME
774 X<$^X> X<$EXECUTABLE_NAME>
776 The name used to execute the current copy of Perl, from C's
777 C<argv[0]> or (where supported) F</proc/self/exe>.
779 Depending on the host operating system, the value of C<$^X> may be
780 a relative or absolute pathname of the perl program file, or may
781 be the string used to invoke perl but not the pathname of the
782 perl program file. Also, most operating systems permit invoking
783 programs that are not in the PATH environment variable, so there
784 is no guarantee that the value of C<$^X> is in PATH. For VMS, the
785 value may or may not include a version number.
787 You usually can use the value of C<$^X> to re-invoke an independent
788 copy of the same perl that is currently running, e.g.,
790 @first_run = `$^X -le "print int rand 100 for 1..100"`;
792 But recall that not all operating systems support forking or
793 capturing of the output of commands, so this complex statement
796 It is not safe to use the value of C<$^X> as a path name of a file,
797 as some operating systems that have a mandatory suffix on
798 executable files do not require use of the suffix when invoking
799 a command. To convert the value of C<$^X> to a path name, use the
800 following statements:
802 # Build up a set of file names (not command names).
806 $this_perl .= $Config{_exe}
807 unless $this_perl =~ m/$Config{_exe}$/i;
810 Because many operating systems permit anyone with read access to
811 the Perl program file to make a copy of it, patch the copy, and
812 then execute the copy, the security-conscious Perl programmer
813 should take care to invoke the installed copy of perl, not the
814 copy referenced by C<$^X>. The following statements accomplish
815 this goal, and produce a pathname that can be invoked as a
816 command or referenced as a file.
819 my $secure_perl_path = $Config{perlpath};
821 $secure_perl_path .= $Config{_exe}
822 unless $secure_perl_path =~ m/$Config{_exe}$/i;
827 =head2 Variables related to regular expressions
829 Most of the special variables related to regular expressions are side
830 effects. Perl sets these variables when it has a successful match, so
831 you should check the match result before using them. For instance:
833 if( /P(A)TT(ER)N/ ) {
834 print "I found $1 and $2\n";
837 These variables are read-only and dynamically-scoped, unless we note
840 The dynamic nature of the regular expression variables means that
841 their value is limited to the block that they are in, as demonstrated
844 my $outer = 'Wallace and Grommit';
845 my $inner = 'Mutt and Jeff';
847 my $pattern = qr/(\S+) and (\S+)/;
849 sub show_n { print "\$1 is $1; \$2 is $2\n" }
853 show_n() if $outer =~ m/$pattern/;
856 show_n() if $inner =~ m/$pattern/;
862 The output shows that while in the C<OUTER> block, the values of C<$1>
863 and C<$2> are from the match against C<$outer>. Inside the C<INNER>
864 block, the values of C<$1> and C<$2> are from the match against
865 C<$inner>, but only until the end of the block (i.e. the dynamic
866 scope). After the C<INNER> block completes, the values of C<$1> and
867 C<$2> return to the values for the match against C<$outer> even though
868 we have not made another match:
870 $1 is Wallace; $2 is Grommit
871 $1 is Mutt; $2 is Jeff
872 $1 is Wallace; $2 is Grommit
874 =head3 Performance issues
876 Traditionally in Perl, any use of any of the three variables C<$`>, C<$&>
877 or C<$'> (or their C<use English> equivalents) anywhere in the code, caused
878 all subsequent successful pattern matches to make a copy of the matched
879 string, in case the code might subsequently access one of those variables.
880 This imposed a considerable performance penalty across the whole program,
881 so generally the use of these variables has been discouraged.
883 In Perl 5.6.0 the C<@-> and C<@+> dynamic arrays were introduced that
884 supply the indices of successful matches. So you could for example do
889 print $`, $&, $'; # bad: performance hit
891 print # good: no performance hit
892 substr($str, 0, $-[0]),
893 substr($str, $-[0], $+[0]-$-[0]),
896 In Perl 5.10.0 the C</p> match operator flag and the C<${^PREMATCH}>,
897 C<${^MATCH}>, and C<${^POSTMATCH}> variables were introduced, that allowed
898 you to suffer the penalties only on patterns marked with C</p>.
900 In Perl 5.18.0 onwards, perl started noting the presence of each of the
901 three variables separately, and only copied that part of the string
904 $`; $&; "abcdefgh" =~ /d/
906 perl would only copy the "abcd" part of the string. That could make a big
907 difference in something like
909 $str = 'x' x 1_000_000;
911 $str =~ /x/g # one char copied a million times, not a million chars
913 In Perl 5.20.0 a new copy-on-write system was enabled by default, which
914 finally fixes all performance issues with these three variables, and makes
915 them safe to use anywhere.
917 The C<Devel::NYTProf> and C<Devel::FindAmpersand> modules can help you
918 find uses of these problematic match variables in your code.
922 =item $<I<digits>> ($1, $2, ...)
923 X<$1> X<$2> X<$3> X<$I<digits>>
925 Contains the subpattern from the corresponding set of capturing
926 parentheses from the last successful pattern match, not counting patterns
927 matched in nested blocks that have been exited already.
929 Note there is a distinction between a capture buffer which matches
930 the empty string a capture buffer which is optional. Eg, C<(x?)> and
931 C<(x)?> The latter may be undef, the former not.
933 These variables are read-only and dynamically-scoped.
935 Mnemonic: like \digits.
938 X<@{^CAPTURE}> X<@^CAPTURE>
940 An array which exposes the contents of the capture buffers, if any, of
941 the last successful pattern match, not counting patterns matched
942 in nested blocks that have been exited already.
944 Note that the 0 index of @{^CAPTURE} is equivalent to $1, the 1 index
945 is equivalent to $2, etc.
947 if ("foal"=~/(.)(.)(.)(.)/) {
948 print join "-", @{^CAPTURE};
951 should output "f-o-a-l".
953 See also L<<< /$<I<digits>> ($1, $2, ...) >>>, L</%{^CAPTURE}> and
956 Note that unlike most other regex magic variables there is no single
957 letter equivalent to C<@{^CAPTURE}>.
959 This variable was added in 5.25.7
966 The string matched by the last successful pattern match (not counting
967 any matches hidden within a BLOCK or C<eval()> enclosed by the current
970 See L</Performance issues> above for the serious performance implications
971 of using this variable (even once) in your code.
973 This variable is read-only and dynamically-scoped.
975 Mnemonic: like C<&> in some editors.
980 This is similar to C<$&> (C<$MATCH>) except that it does not incur the
981 performance penalty associated with that variable.
983 See L</Performance issues> above.
985 In Perl v5.18 and earlier, it is only guaranteed
986 to return a defined value when the pattern was compiled or executed with
987 the C</p> modifier. In Perl v5.20, the C</p> modifier does nothing, so
988 C<${^MATCH}> does the same thing as C<$MATCH>.
990 This variable was added in Perl v5.10.0.
992 This variable is read-only and dynamically-scoped.
997 X<$`> X<$PREMATCH> X<${^PREMATCH}>
999 The string preceding whatever was matched by the last successful
1000 pattern match, not counting any matches hidden within a BLOCK or C<eval>
1001 enclosed by the current BLOCK.
1003 See L</Performance issues> above for the serious performance implications
1004 of using this variable (even once) in your code.
1006 This variable is read-only and dynamically-scoped.
1008 Mnemonic: C<`> often precedes a quoted string.
1011 X<$`> X<${^PREMATCH}>
1013 This is similar to C<$`> ($PREMATCH) except that it does not incur the
1014 performance penalty associated with that variable.
1016 See L</Performance issues> above.
1018 In Perl v5.18 and earlier, it is only guaranteed
1019 to return a defined value when the pattern was compiled or executed with
1020 the C</p> modifier. In Perl v5.20, the C</p> modifier does nothing, so
1021 C<${^PREMATCH}> does the same thing as C<$PREMATCH>.
1023 This variable was added in Perl v5.10.0.
1025 This variable is read-only and dynamically-scoped.
1030 X<$'> X<$POSTMATCH> X<${^POSTMATCH}> X<@->
1032 The string following whatever was matched by the last successful
1033 pattern match (not counting any matches hidden within a BLOCK or C<eval()>
1034 enclosed by the current BLOCK). Example:
1036 local $_ = 'abcdefghi';
1038 print "$`:$&:$'\n"; # prints abc:def:ghi
1040 See L</Performance issues> above for the serious performance implications
1041 of using this variable (even once) in your code.
1043 This variable is read-only and dynamically-scoped.
1045 Mnemonic: C<'> often follows a quoted string.
1048 X<${^POSTMATCH}> X<$'> X<$POSTMATCH>
1050 This is similar to C<$'> (C<$POSTMATCH>) except that it does not incur the
1051 performance penalty associated with that variable.
1053 See L</Performance issues> above.
1055 In Perl v5.18 and earlier, it is only guaranteed
1056 to return a defined value when the pattern was compiled or executed with
1057 the C</p> modifier. In Perl v5.20, the C</p> modifier does nothing, so
1058 C<${^POSTMATCH}> does the same thing as C<$POSTMATCH>.
1060 This variable was added in Perl v5.10.0.
1062 This variable is read-only and dynamically-scoped.
1064 =item $LAST_PAREN_MATCH
1067 X<$+> X<$LAST_PAREN_MATCH>
1069 The text matched by the highest used capture group of the last
1070 successful search pattern. It is logically equivalent to the highest
1071 numbered capture variable (C<$1>, C<$2>, ...) which has a defined value.
1073 This is useful if you don't know which one of a set of alternative patterns
1074 matched. For example:
1076 /Version: (.*)|Revision: (.*)/ && ($rev = $+);
1078 This variable is read-only and dynamically-scoped.
1080 Mnemonic: be positive and forward looking.
1082 =item $LAST_SUBMATCH_RESULT
1085 X<$^N> X<$LAST_SUBMATCH_RESULT>
1087 The text matched by the used group most-recently closed (i.e. the group
1088 with the rightmost closing parenthesis) of the last successful search
1089 pattern. This is subtly different from C<$+>. For example in
1091 "ab" =~ /^((.)(.))$/
1095 $1,$^N have the value "ab"
1096 $2 has the value "a"
1097 $3,$+ have the value "b"
1099 This is primarily used inside C<(?{...})> blocks for examining text
1100 recently matched. For example, to effectively capture text to a variable
1101 (in addition to C<$1>, C<$2>, etc.), replace C<(...)> with
1103 (?:(...)(?{ $var = $^N }))
1105 By setting and then using C<$var> in this way relieves you from having to
1106 worry about exactly which numbered set of parentheses they are.
1108 This variable was added in Perl v5.8.0.
1110 Mnemonic: the (possibly) Nested parenthesis that most recently closed.
1112 =item @LAST_MATCH_END
1115 X<@+> X<@LAST_MATCH_END>
1117 This array holds the offsets of the ends of the last successful
1118 submatches in the currently active dynamic scope. C<$+[0]> is
1119 the offset into the string of the end of the entire match. This
1120 is the same value as what the C<pos> function returns when called
1121 on the variable that was matched against. The I<n>th element
1122 of this array holds the offset of the I<n>th submatch, so
1123 C<$+[1]> is the offset past where C<$1> ends, C<$+[2]> the offset
1124 past where C<$2> ends, and so on. You can use C<$#+> to determine
1125 how many subgroups were in the last successful match. See the
1126 examples given for the C<@-> variable.
1128 This variable was added in Perl v5.6.0.
1132 =item %LAST_PAREN_MATCH
1135 X<%+> X<%LAST_PAREN_MATCH> X<%{^CAPTURE}>
1137 Similar to C<@+>, the C<%+> hash allows access to the named capture
1138 buffers, should they exist, in the last successful match in the
1139 currently active dynamic scope.
1141 For example, C<$+{foo}> is equivalent to C<$1> after the following match:
1143 'foo' =~ /(?<foo>foo)/;
1145 The keys of the C<%+> hash list only the names of buffers that have
1146 captured (and that are thus associated to defined values).
1148 If multiple distinct capture groups have the same name, then
1149 C<$+{NAME}> will refer to the leftmost defined group in the match.
1151 The underlying behaviour of C<%+> is provided by the
1152 L<Tie::Hash::NamedCapture> module.
1154 B<Note:> C<%-> and C<%+> are tied views into a common internal hash
1155 associated with the last successful regular expression. Therefore mixing
1156 iterative access to them via C<each> may have unpredictable results.
1157 Likewise, if the last successful match changes, then the results may be
1160 This variable was added in Perl v5.10.0. The C<%{^CAPTURE}> alias was
1163 This variable is read-only and dynamically-scoped.
1165 =item @LAST_MATCH_START
1168 X<@-> X<@LAST_MATCH_START>
1170 C<$-[0]> is the offset of the start of the last successful match.
1171 C<$-[I<n>]> is the offset of the start of the substring matched by
1172 I<n>-th subpattern, or undef if the subpattern did not match.
1174 Thus, after a match against C<$_>, C<$&> coincides with C<substr $_, $-[0],
1175 $+[0] - $-[0]>. Similarly, $I<n> coincides with C<substr $_, $-[n],
1176 $+[n] - $-[n]> if C<$-[n]> is defined, and $+ coincides with
1177 C<substr $_, $-[$#-], $+[$#-] - $-[$#-]>. One can use C<$#-> to find the
1178 last matched subgroup in the last successful match. Contrast with
1179 C<$#+>, the number of subgroups in the regular expression. Compare
1182 This array holds the offsets of the beginnings of the last
1183 successful submatches in the currently active dynamic scope.
1184 C<$-[0]> is the offset into the string of the beginning of the
1185 entire match. The I<n>th element of this array holds the offset
1186 of the I<n>th submatch, so C<$-[1]> is the offset where C<$1>
1187 begins, C<$-[2]> the offset where C<$2> begins, and so on.
1189 After a match against some variable C<$var>:
1193 =item C<$`> is the same as C<substr($var, 0, $-[0])>
1195 =item C<$&> is the same as C<substr($var, $-[0], $+[0] - $-[0])>
1197 =item C<$'> is the same as C<substr($var, $+[0])>
1199 =item C<$1> is the same as C<substr($var, $-[1], $+[1] - $-[1])>
1201 =item C<$2> is the same as C<substr($var, $-[2], $+[2] - $-[2])>
1203 =item C<$3> is the same as C<substr($var, $-[3], $+[3] - $-[3])>
1207 This variable was added in Perl v5.6.0.
1209 =item %{^CAPTURE_ALL}
1215 Similar to C<%+>, this variable allows access to the named capture groups
1216 in the last successful match in the currently active dynamic scope. To
1217 each capture group name found in the regular expression, it associates a
1218 reference to an array containing the list of values captured by all
1219 buffers with that name (should there be several of them), in the order
1224 if ('1234' =~ /(?<A>1)(?<B>2)(?<A>3)(?<B>4)/) {
1225 foreach my $bufname (sort keys %-) {
1226 my $ary = $-{$bufname};
1227 foreach my $idx (0..$#$ary) {
1228 print "\$-{$bufname}[$idx] : ",
1229 (defined($ary->[$idx])
1244 The keys of the C<%-> hash correspond to all buffer names found in
1245 the regular expression.
1247 The behaviour of C<%-> is implemented via the
1248 L<Tie::Hash::NamedCapture> module.
1250 B<Note:> C<%-> and C<%+> are tied views into a common internal hash
1251 associated with the last successful regular expression. Therefore mixing
1252 iterative access to them via C<each> may have unpredictable results.
1253 Likewise, if the last successful match changes, then the results may be
1256 This variable was added in Perl v5.10.0. The C<%{^CAPTURE_ALL}> alias was
1259 This variable is read-only and dynamically-scoped.
1261 =item $LAST_REGEXP_CODE_RESULT
1264 X<$^R> X<$LAST_REGEXP_CODE_RESULT>
1266 The result of evaluation of the last successful C<(?{ code })>
1267 regular expression assertion (see L<perlre>). May be written to.
1269 This variable was added in Perl 5.005.
1271 =item ${^RE_COMPILE_RECURSION_LIMIT}
1272 X<${^RE_COMPILE_RECURSION_LIMIT}>
1274 The current value giving the maximum number of open but unclosed
1275 parenthetical groups there may be at any point during a regular
1276 expression compilation. The default is currently 1000 nested groups.
1277 You may adjust it depending on your needs and the amount of memory
1280 This variable was added in Perl v5.30.0.
1282 =item ${^RE_DEBUG_FLAGS}
1283 X<${^RE_DEBUG_FLAGS}>
1285 The current value of the regex debugging flags. Set to 0 for no debug output
1286 even when the C<re 'debug'> module is loaded. See L<re> for details.
1288 This variable was added in Perl v5.10.0.
1290 =item ${^RE_TRIE_MAXBUF}
1291 X<${^RE_TRIE_MAXBUF}>
1293 Controls how certain regex optimisations are applied and how much memory they
1294 utilize. This value by default is 65536 which corresponds to a 512kB
1295 temporary cache. Set this to a higher value to trade
1296 memory for speed when matching large alternations. Set
1297 it to a lower value if you want the optimisations to
1298 be as conservative of memory as possible but still occur, and set it to a
1299 negative value to prevent the optimisation and conserve the most memory.
1300 Under normal situations this variable should be of no interest to you.
1302 This variable was added in Perl v5.10.0.
1306 =head2 Variables related to filehandles
1308 Variables that depend on the currently selected filehandle may be set
1309 by calling an appropriate object method on the C<IO::Handle> object,
1310 although this is less efficient than using the regular built-in
1311 variables. (Summary lines below for this contain the word HANDLE.)
1316 after which you may use either
1322 HANDLE->method(EXPR)
1324 Each method returns the old value of the C<IO::Handle> attribute. The
1325 methods each take an optional EXPR, which, if supplied, specifies the
1326 new value for the C<IO::Handle> attribute in question. If not
1327 supplied, most methods do nothing to the current value--except for
1328 C<autoflush()>, which will assume a 1 for you, just to be different.
1330 Because loading in the C<IO::Handle> class is an expensive operation,
1331 you should learn how to use the regular built-in variables.
1333 A few of these variables are considered "read-only". This means that
1334 if you try to assign to this variable, either directly or indirectly
1335 through a reference, you'll raise a run-time exception.
1337 You should be very careful when modifying the default values of most
1338 special variables described in this document. In most cases you want
1339 to localize these variables before changing them, since if you don't,
1340 the change may affect other modules which rely on the default values
1341 of the special variables that you have changed. This is one of the
1342 correct ways to read the whole file at once:
1344 open my $fh, "<", "foo" or die $!;
1345 local $/; # enable localized slurp mode
1346 my $content = <$fh>;
1349 But the following code is quite bad:
1351 open my $fh, "<", "foo" or die $!;
1352 undef $/; # enable slurp mode
1353 my $content = <$fh>;
1356 since some other module, may want to read data from some file in the
1357 default "line mode", so if the code we have just presented has been
1358 executed, the global value of C<$/> is now changed for any other code
1359 running inside the same Perl interpreter.
1361 Usually when a variable is localized you want to make sure that this
1362 change affects the shortest scope possible. So unless you are already
1363 inside some short C<{}> block, you should create one yourself. For
1367 open my $fh, "<", "foo" or die $!;
1374 Here is an example of how your own code can go broken:
1384 # do something with $_
1387 You probably expect this code to print the equivalent of
1391 but instead you get:
1395 Why? Because C<nasty_break()> modifies C<$\> without localizing it
1396 first. The value you set in C<nasty_break()> is still there when you
1397 return. The fix is to add C<local()> so the value doesn't leak out of
1402 It's easy to notice the problem in such a short example, but in more
1403 complicated code you are looking for trouble if you don't localize
1404 changes to the special variables.
1411 Contains the name of the current file when reading from C<< <> >>.
1416 The array C<@ARGV> contains the command-line arguments intended for
1417 the script. C<$#ARGV> is generally the number of arguments minus
1418 one, because C<$ARGV[0]> is the first argument, I<not> the program's
1419 command name itself. See L</$0> for the command name.
1424 The special filehandle that iterates over command-line filenames in
1425 C<@ARGV>. Usually written as the null filehandle in the angle operator
1426 C<< <> >>. Note that currently C<ARGV> only has its magical effect
1427 within the C<< <> >> operator; elsewhere it is just a plain filehandle
1428 corresponding to the last file opened by C<< <> >>. In particular,
1429 passing C<\*ARGV> as a parameter to a function that expects a filehandle
1430 may not cause your function to automatically read the contents of all the
1436 The special filehandle that points to the currently open output file
1437 when doing edit-in-place processing with B<-i>. Useful when you have
1438 to do a lot of inserting and don't want to keep modifying C<$_>. See
1439 L<perlrun> for the B<-i> switch.
1441 =item IO::Handle->output_field_separator( EXPR )
1443 =item $OUTPUT_FIELD_SEPARATOR
1448 X<$,> X<$OFS> X<$OUTPUT_FIELD_SEPARATOR>
1450 The output field separator for the print operator. If defined, this
1451 value is printed between each of print's arguments. Default is C<undef>.
1453 You cannot call C<output_field_separator()> on a handle, only as a
1454 static method. See L<IO::Handle|IO::Handle>.
1456 Mnemonic: what is printed when there is a "," in your print statement.
1458 =item HANDLE->input_line_number( EXPR )
1460 =item $INPUT_LINE_NUMBER
1465 X<$.> X<$NR> X<$INPUT_LINE_NUMBER> X<line number>
1467 Current line number for the last filehandle accessed.
1469 Each filehandle in Perl counts the number of lines that have been read
1470 from it. (Depending on the value of C<$/>, Perl's idea of what
1471 constitutes a line may not match yours.) When a line is read from a
1472 filehandle (via C<readline()> or C<< <> >>), or when C<tell()> or
1473 C<seek()> is called on it, C<$.> becomes an alias to the line counter
1474 for that filehandle.
1476 You can adjust the counter by assigning to C<$.>, but this will not
1477 actually move the seek pointer. I<Localizing C<$.> will not localize
1478 the filehandle's line count>. Instead, it will localize perl's notion
1479 of which filehandle C<$.> is currently aliased to.
1481 C<$.> is reset when the filehandle is closed, but B<not> when an open
1482 filehandle is reopened without an intervening C<close()>. For more
1483 details, see L<perlop/"IE<sol>O Operators">. Because C<< <> >> never does
1484 an explicit close, line numbers increase across C<ARGV> files (but see
1485 examples in L<perlfunc/eof>).
1487 You can also use C<< HANDLE->input_line_number(EXPR) >> to access the
1488 line counter for a given filehandle without having to worry about
1489 which handle you last accessed.
1491 Mnemonic: many programs use "." to mean the current line number.
1493 =item IO::Handle->input_record_separator( EXPR )
1495 =item $INPUT_RECORD_SEPARATOR
1500 X<$/> X<$RS> X<$INPUT_RECORD_SEPARATOR>
1502 The input record separator, newline by default. This influences Perl's
1503 idea of what a "line" is. Works like B<awk>'s RS variable, including
1504 treating empty lines as a terminator if set to the null string (an
1505 empty line cannot contain any spaces or tabs). You may set it to a
1506 multi-character string to match a multi-character terminator, or to
1507 C<undef> to read through the end of file. Setting it to C<"\n\n">
1508 means something slightly different than setting to C<"">, if the file
1509 contains consecutive empty lines. Setting to C<""> will treat two or
1510 more consecutive empty lines as a single empty line. Setting to
1511 C<"\n\n"> will blindly assume that the next input character belongs to
1512 the next paragraph, even if it's a newline.
1514 local $/; # enable "slurp" mode
1515 local $_ = <FH>; # whole file now here
1518 Remember: the value of C<$/> is a string, not a regex. B<awk> has to
1519 be better for something. :-)
1521 Setting C<$/> to an empty string -- the so-called I<paragraph mode> -- merits
1522 special attention. When C<$/> is set to C<""> and the entire file is read in
1523 with that setting, any sequence of consecutive newlines C<"\n\n"> at the
1524 beginning of the file is discarded. With the exception of the final record in
1525 the file, each sequence of characters ending in two or more newlines is
1526 treated as one record and is read in to end in exactly two newlines. If the
1527 last record in the file ends in zero or one consecutive newlines, that record
1528 is read in with that number of newlines. If the last record ends in two or
1529 more consecutive newlines, it is read in with two newlines like all preceding
1532 Suppose we wrote the following string to a file:
1534 my $string = "\n\n\n";
1535 $string .= "alpha beta\ngamma delta\n\n\n";
1536 $string .= "epsilon zeta eta\n\n";
1537 $string .= "theta\n";
1539 my $file = 'simple_file.txt';
1540 open my $OUT, '>', $file or die;
1544 Now we read that file in paragraph mode:
1546 local $/ = ""; # paragraph mode
1547 open my $IN, '<', $file or die;
1548 my @records = <$IN>;
1551 C<@records> will consist of these 3 strings:
1554 "alpha beta\ngamma delta\n\n",
1555 "epsilon zeta eta\n\n",
1559 Setting C<$/> to a reference to an integer, scalar containing an
1560 integer, or scalar that's convertible to an integer will attempt to
1561 read records instead of lines, with the maximum record size being the
1562 referenced integer number of characters. So this:
1564 local $/ = \32768; # or \"32768", or \$var_containing_32768
1565 open my $fh, "<", $myfile or die $!;
1568 will read a record of no more than 32768 characters from $fh. If you're
1569 not reading from a record-oriented file (or your OS doesn't have
1570 record-oriented files), then you'll likely get a full chunk of data
1571 with every read. If a record is larger than the record size you've
1572 set, you'll get the record back in pieces. Trying to set the record
1573 size to zero or less is deprecated and will cause $/ to have the value
1574 of "undef", which will cause reading in the (rest of the) whole file.
1576 As of 5.19.9 setting C<$/> to any other form of reference will throw a
1577 fatal exception. This is in preparation for supporting new ways to set
1578 C<$/> in the future.
1580 On VMS only, record reads bypass PerlIO layers and any associated
1581 buffering, so you must not mix record and non-record reads on the
1582 same filehandle. Record mode mixes with line mode only when the
1583 same buffering layer is in use for both modes.
1585 You cannot call C<input_record_separator()> on a handle, only as a
1586 static method. See L<IO::Handle|IO::Handle>.
1588 See also L<perlport/"Newlines">. Also see L</$.>.
1590 Mnemonic: / delimits line boundaries when quoting poetry.
1592 =item IO::Handle->output_record_separator( EXPR )
1594 =item $OUTPUT_RECORD_SEPARATOR
1599 X<$\> X<$ORS> X<$OUTPUT_RECORD_SEPARATOR>
1601 The output record separator for the print operator. If defined, this
1602 value is printed after the last of print's arguments. Default is C<undef>.
1604 You cannot call C<output_record_separator()> on a handle, only as a
1605 static method. See L<IO::Handle|IO::Handle>.
1607 Mnemonic: you set C<$\> instead of adding "\n" at the end of the print.
1608 Also, it's just like C<$/>, but it's what you get "back" from Perl.
1610 =item HANDLE->autoflush( EXPR )
1612 =item $OUTPUT_AUTOFLUSH
1615 X<$|> X<autoflush> X<flush> X<$OUTPUT_AUTOFLUSH>
1617 If set to nonzero, forces a flush right away and after every write or
1618 print on the currently selected output channel. Default is 0
1619 (regardless of whether the channel is really buffered by the system or
1620 not; C<$|> tells you only whether you've asked Perl explicitly to
1621 flush after each write). STDOUT will typically be line buffered if
1622 output is to the terminal and block buffered otherwise. Setting this
1623 variable is useful primarily when you are outputting to a pipe or
1624 socket, such as when you are running a Perl program under B<rsh> and
1625 want to see the output as it's happening. This has no effect on input
1626 buffering. See L<perlfunc/getc> for that. See L<perlfunc/select> on
1627 how to select the output channel. See also L<IO::Handle>.
1629 Mnemonic: when you want your pipes to be piping hot.
1634 This read-only variable contains a reference to the last-read filehandle.
1635 This is set by C<< <HANDLE> >>, C<readline>, C<tell>, C<eof> and C<seek>.
1636 This is the same handle that C<$.> and C<tell> and C<eof> without arguments
1637 use. It is also the handle used when Perl appends ", <STDIN> line 1" to
1638 an error or warning message.
1640 This variable was added in Perl v5.18.0.
1644 =head3 Variables related to formats
1646 The special variables for formats are a subset of those for
1647 filehandles. See L<perlform> for more information about Perl's
1655 X<$^A> X<$ACCUMULATOR>
1657 The current value of the C<write()> accumulator for C<format()> lines.
1658 A format contains C<formline()> calls that put their result into
1659 C<$^A>. After calling its format, C<write()> prints out the contents
1660 of C<$^A> and empties. So you never really see the contents of C<$^A>
1661 unless you call C<formline()> yourself and then look at it. See
1662 L<perlform> and L<perlfunc/"formline PICTURE,LIST">.
1664 =item IO::Handle->format_formfeed(EXPR)
1666 =item $FORMAT_FORMFEED
1669 X<$^L> X<$FORMAT_FORMFEED>
1671 What formats output as a form feed. The default is C<\f>.
1673 You cannot call C<format_formfeed()> on a handle, only as a static
1674 method. See L<IO::Handle|IO::Handle>.
1676 =item HANDLE->format_page_number(EXPR)
1678 =item $FORMAT_PAGE_NUMBER
1681 X<$%> X<$FORMAT_PAGE_NUMBER>
1683 The current page number of the currently selected output channel.
1685 Mnemonic: C<%> is page number in B<nroff>.
1687 =item HANDLE->format_lines_left(EXPR)
1689 =item $FORMAT_LINES_LEFT
1692 X<$-> X<$FORMAT_LINES_LEFT>
1694 The number of lines left on the page of the currently selected output
1697 Mnemonic: lines_on_page - lines_printed.
1699 =item IO::Handle->format_line_break_characters EXPR
1701 =item $FORMAT_LINE_BREAK_CHARACTERS
1704 X<$:> X<FORMAT_LINE_BREAK_CHARACTERS>
1706 The current set of characters after which a string may be broken to
1707 fill continuation fields (starting with C<^>) in a format. The default is
1708 S<" \n-">, to break on a space, newline, or a hyphen.
1710 You cannot call C<format_line_break_characters()> on a handle, only as
1711 a static method. See L<IO::Handle|IO::Handle>.
1713 Mnemonic: a "colon" in poetry is a part of a line.
1715 =item HANDLE->format_lines_per_page(EXPR)
1717 =item $FORMAT_LINES_PER_PAGE
1720 X<$=> X<$FORMAT_LINES_PER_PAGE>
1722 The current page length (printable lines) of the currently selected
1723 output channel. The default is 60.
1725 Mnemonic: = has horizontal lines.
1727 =item HANDLE->format_top_name(EXPR)
1729 =item $FORMAT_TOP_NAME
1732 X<$^> X<$FORMAT_TOP_NAME>
1734 The name of the current top-of-page format for the currently selected
1735 output channel. The default is the name of the filehandle with C<_TOP>
1736 appended. For example, the default format top name for the C<STDOUT>
1737 filehandle is C<STDOUT_TOP>.
1739 Mnemonic: points to top of page.
1741 =item HANDLE->format_name(EXPR)
1746 X<$~> X<$FORMAT_NAME>
1748 The name of the current report format for the currently selected
1749 output channel. The default format name is the same as the filehandle
1750 name. For example, the default format name for the C<STDOUT>
1751 filehandle is just C<STDOUT>.
1753 Mnemonic: brother to C<$^>.
1757 =head2 Error Variables
1758 X<error> X<exception>
1760 The variables C<$@>, C<$!>, C<$^E>, and C<$?> contain information
1761 about different types of error conditions that may appear during
1762 execution of a Perl program. The variables are shown ordered by
1763 the "distance" between the subsystem which reported the error and
1764 the Perl process. They correspond to errors detected by the Perl
1765 interpreter, C library, operating system, or an external program,
1768 To illustrate the differences between these variables, consider the
1769 following Perl expression, which uses a single-quoted string. After
1770 execution of this statement, perl may have set all four special error
1774 open my $pipe, "/cdrom/install |" or die $!;
1776 close $pipe or die "bad pipe: $?, $!";
1779 When perl executes the C<eval()> expression, it translates the
1780 C<open()>, C<< <PIPE> >>, and C<close> calls in the C run-time library
1781 and thence to the operating system kernel. perl sets C<$!> to
1782 the C library's C<errno> if one of these calls fails.
1784 C<$@> is set if the string to be C<eval>-ed did not compile (this may
1785 happen if C<open> or C<close> were imported with bad prototypes), or
1786 if Perl code executed during evaluation C<die()>d. In these cases the
1787 value of C<$@> is the compile error, or the argument to C<die> (which
1788 will interpolate C<$!> and C<$?>). (See also L<Fatal>, though.)
1790 Under a few operating systems, C<$^E> may contain a more verbose error
1791 indicator, such as in this case, "CDROM tray not closed." Systems that
1792 do not support extended error messages leave C<$^E> the same as C<$!>.
1794 Finally, C<$?> may be set to a non-0 value if the external program
1795 F</cdrom/install> fails. The upper eight bits reflect specific error
1796 conditions encountered by the program (the program's C<exit()> value).
1797 The lower eight bits reflect mode of failure, like signal death and
1798 core dump information. See L<wait(2)> for details. In contrast to
1799 C<$!> and C<$^E>, which are set only if an error condition is detected,
1800 the variable C<$?> is set on each C<wait> or pipe C<close>,
1801 overwriting the old value. This is more like C<$@>, which on every
1802 C<eval()> is always set on failure and cleared on success.
1804 For more details, see the individual descriptions at C<$@>, C<$!>,
1809 =item ${^CHILD_ERROR_NATIVE}
1810 X<$^CHILD_ERROR_NATIVE>
1812 The native status returned by the last pipe close, backtick (C<``>)
1813 command, successful call to C<wait()> or C<waitpid()>, or from the
1814 C<system()> operator. On POSIX-like systems this value can be decoded
1815 with the WIFEXITED, WEXITSTATUS, WIFSIGNALED, WTERMSIG, WIFSTOPPED,
1816 WSTOPSIG and WIFCONTINUED functions provided by the L<POSIX> module.
1818 Under VMS this reflects the actual VMS exit status; i.e. it is the
1819 same as C<$?> when the pragma C<use vmsish 'status'> is in effect.
1821 This variable was added in Perl v5.10.0.
1823 =item $EXTENDED_OS_ERROR
1826 X<$^E> X<$EXTENDED_OS_ERROR>
1828 Error information specific to the current operating system. At the
1829 moment, this differs from C<L</$!>> under only VMS, OS/2, and Win32 (and
1830 for MacPerl). On all other platforms, C<$^E> is always just the same
1833 Under VMS, C<$^E> provides the VMS status value from the last system
1834 error. This is more specific information about the last system error
1835 than that provided by C<$!>. This is particularly important when C<$!>
1836 is set to B<EVMSERR>.
1838 Under OS/2, C<$^E> is set to the error code of the last call to OS/2
1839 API either via CRT, or directly from perl.
1841 Under Win32, C<$^E> always returns the last error information reported
1842 by the Win32 call C<GetLastError()> which describes the last error
1843 from within the Win32 API. Most Win32-specific code will report errors
1844 via C<$^E>. ANSI C and Unix-like calls set C<errno> and so most
1845 portable Perl code will report errors via C<$!>.
1847 Caveats mentioned in the description of C<L</$!>> generally apply to
1850 This variable was added in Perl 5.003.
1852 Mnemonic: Extra error explanation.
1854 =item $EXCEPTIONS_BEING_CAUGHT
1857 X<$^S> X<$EXCEPTIONS_BEING_CAUGHT>
1859 Current state of the interpreter.
1862 --------- -------------------------------------
1863 undef Parsing module, eval, or main program
1864 true (1) Executing an eval
1867 The first state may happen in C<$SIG{__DIE__}> and C<$SIG{__WARN__}>
1870 The English name $EXCEPTIONS_BEING_CAUGHT is slightly misleading, because
1871 the C<undef> value does not indicate whether exceptions are being caught,
1872 since compilation of the main program does not catch exceptions.
1874 This variable was added in Perl 5.004.
1881 The current value of the warning switch, initially true if B<-w> was
1882 used, false otherwise, but directly modifiable.
1884 See also L<warnings>.
1886 Mnemonic: related to the B<-w> switch.
1888 =item ${^WARNING_BITS}
1891 The current set of warning checks enabled by the C<use warnings> pragma.
1892 It has the same scoping as the C<$^H> and C<%^H> variables. The exact
1893 values are considered internal to the L<warnings> pragma and may change
1894 between versions of Perl.
1896 This variable was added in Perl v5.6.0.
1903 X<$!> X<$ERRNO> X<$OS_ERROR>
1905 When referenced, C<$!> retrieves the current value
1906 of the C C<errno> integer variable.
1907 If C<$!> is assigned a numerical value, that value is stored in C<errno>.
1908 When referenced as a string, C<$!> yields the system error string
1909 corresponding to C<errno>.
1911 Many system or library calls set C<errno> if they fail,
1912 to indicate the cause of failure. They usually do B<not>
1913 set C<errno> to zero if they succeed. This means C<errno>,
1914 hence C<$!>, is meaningful only I<immediately> after a B<failure>:
1916 if (open my $fh, "<", $filename) {
1917 # Here $! is meaningless.
1921 # ONLY here is $! meaningful.
1923 # Already here $! might be meaningless.
1925 # Since here we might have either success or failure,
1926 # $! is meaningless.
1928 Here, I<meaningless> means that C<$!> may be unrelated to the outcome
1929 of the C<open()> operator. Assignment to C<$!> is similarly ephemeral.
1930 It can be used immediately before invoking the C<die()> operator,
1931 to set the exit value, or to inspect the system error string
1932 corresponding to error I<n>, or to restore C<$!> to a meaningful state.
1934 Mnemonic: What just went bang?
1941 X<%!> X<%OS_ERROR> X<%ERRNO>
1943 Each element of C<%!> has a true value only if C<$!> is set to that
1944 value. For example, C<$!{ENOENT}> is true if and only if the current
1945 value of C<$!> is C<ENOENT>; that is, if the most recent error was "No
1946 such file or directory" (or its moral equivalent: not all operating
1947 systems give that exact error, and certainly not all languages). The
1948 specific true value is not guaranteed, but in the past has generally
1949 been the numeric value of C<$!>. To check if a particular key is
1950 meaningful on your system, use C<exists $!{the_key}>; for a list of legal
1951 keys, use C<keys %!>. See L<Errno> for more information, and also see
1954 This variable was added in Perl 5.005.
1959 X<$?> X<$CHILD_ERROR>
1961 The status returned by the last pipe close, backtick (C<``>) command,
1962 successful call to C<wait()> or C<waitpid()>, or from the C<system()>
1963 operator. This is just the 16-bit status word returned by the
1964 traditional Unix C<wait()> system call (or else is made up to look
1965 like it). Thus, the exit value of the subprocess is really (C<<< $? >>
1966 8 >>>), and C<$? & 127> gives which signal, if any, the process died
1967 from, and C<$? & 128> reports whether there was a core dump.
1969 Additionally, if the C<h_errno> variable is supported in C, its value
1970 is returned via C<$?> if any C<gethost*()> function fails.
1972 If you have installed a signal handler for C<SIGCHLD>, the
1973 value of C<$?> will usually be wrong outside that handler.
1975 Inside an C<END> subroutine C<$?> contains the value that is going to be
1976 given to C<exit()>. You can modify C<$?> in an C<END> subroutine to
1977 change the exit status of your program. For example:
1980 $? = 1 if $? == 255; # die would make it 255
1983 Under VMS, the pragma C<use vmsish 'status'> makes C<$?> reflect the
1984 actual VMS exit status, instead of the default emulation of POSIX
1985 status; see L<perlvms/$?> for details.
1987 Mnemonic: similar to B<sh> and B<ksh>.
1992 X<$@> X<$EVAL_ERROR>
1994 The Perl error from the last C<eval> operator, i.e. the last exception that
1995 was caught. For C<eval BLOCK>, this is either a runtime error message or the
1996 string or reference C<die> was called with. The C<eval STRING> form also
1997 catches syntax errors and other compile time exceptions.
1999 If no error occurs, C<eval> sets C<$@> to the empty string.
2001 Warning messages are not collected in this variable. You can, however,
2002 set up a routine to process warnings by setting C<$SIG{__WARN__}> as
2003 described in L</%SIG>.
2005 Mnemonic: Where was the error "at"?
2009 =head2 Variables related to the interpreter state
2011 These variables provide information about the current interpreter state.
2018 X<$^C> X<$COMPILING>
2020 The current value of the flag associated with the B<-c> switch.
2021 Mainly of use with B<-MO=...> to allow code to alter its behavior
2022 when being compiled, such as for example to C<AUTOLOAD> at compile
2023 time rather than normal, deferred loading. Setting
2024 C<$^C = 1> is similar to calling C<B::minus_c>.
2026 This variable was added in Perl v5.6.0.
2031 X<$^D> X<$DEBUGGING>
2033 The current value of the debugging flags. May be read or set. Like its
2034 L<command-line equivalent|perlrun/B<-D>I<letters>>, you can use numeric
2035 or symbolic values, e.g. C<$^D = 10> or C<$^D = "st">. See
2036 L<perlrun/B<-D>I<number>>. The contents of this variable also affects the
2037 debugger operation. See L<perldebguts/Debugger Internals>.
2039 Mnemonic: value of B<-D> switch.
2044 This variable is no longer supported.
2046 It used to hold the I<object reference> to the C<Encode> object that was
2047 used to convert the source code to Unicode.
2049 Its purpose was to allow your non-ASCII Perl
2050 scripts not to have to be written in UTF-8; this was
2051 useful before editors that worked on UTF-8 encoded text were common, but
2052 that was long ago. It caused problems, such as affecting the operation
2053 of other modules that weren't expecting it, causing general mayhem.
2055 If you need something like this functionality, it is recommended that use
2056 you a simple source filter, such as L<Filter::Encoding>.
2058 If you are coming here because code of yours is being adversely affected
2059 by someone's use of this variable, you can usually work around it by
2064 near the beginning of the functions that are getting broken. This
2065 undefines the variable during the scope of execution of the including
2068 This variable was added in Perl 5.8.2 and removed in 5.26.0.
2069 Setting it to anything other than C<undef> was made fatal in Perl 5.28.0.
2071 =item ${^GLOBAL_PHASE}
2074 The current phase of the perl interpreter.
2076 Possible values are:
2082 The C<PerlInterpreter*> is being constructed via C<perl_construct>. This
2083 value is mostly there for completeness and for use via the
2084 underlying C variable C<PL_phase>. It's not really possible for Perl
2085 code to be executed unless construction of the interpreter is
2090 This is the global compile-time. That includes, basically, every
2091 C<BEGIN> block executed directly or indirectly from during the
2092 compile-time of the top-level program.
2094 This phase is not called "BEGIN" to avoid confusion with
2095 C<BEGIN>-blocks, as those are executed during compile-time of any
2096 compilation unit, not just the top-level program. A new, localised
2097 compile-time entered at run-time, for example by constructs as
2098 C<eval "use SomeModule"> are not global interpreter phases, and
2099 therefore aren't reflected by C<${^GLOBAL_PHASE}>.
2103 Execution of any C<CHECK> blocks.
2107 Similar to "CHECK", but for C<INIT>-blocks, not C<CHECK> blocks.
2111 The main run-time, i.e. the execution of C<PL_main_root>.
2115 Execution of any C<END> blocks.
2123 Also note that there's no value for UNITCHECK-blocks. That's because
2124 those are run for each compilation unit individually, and therefore is
2125 not a global interpreter phase.
2127 Not every program has to go through each of the possible phases, but
2128 transition from one phase to another can only happen in the order
2129 described in the above list.
2131 An example of all of the phases Perl code can see:
2133 BEGIN { print "compile-time: ${^GLOBAL_PHASE}\n" }
2135 INIT { print "init-time: ${^GLOBAL_PHASE}\n" }
2137 CHECK { print "check-time: ${^GLOBAL_PHASE}\n" }
2140 package Print::Phase;
2143 my ($class, $time) = @_;
2144 return bless \$time, $class;
2149 print "$$self: ${^GLOBAL_PHASE}\n";
2153 print "run-time: ${^GLOBAL_PHASE}\n";
2155 my $runtime = Print::Phase->new(
2156 "lexical variables are garbage collected before END"
2159 END { print "end-time: ${^GLOBAL_PHASE}\n" }
2161 our $destruct = Print::Phase->new(
2162 "package variables are garbage collected after END"
2171 lexical variables are garbage collected before END: RUN
2173 package variables are garbage collected after END: DESTRUCT
2175 This variable was added in Perl 5.14.0.
2180 WARNING: This variable is strictly for
2181 internal use only. Its availability,
2182 behavior, and contents are subject to change without notice.
2184 This variable contains compile-time hints for the Perl interpreter. At the
2185 end of compilation of a BLOCK the value of this variable is restored to the
2186 value when the interpreter started to compile the BLOCK.
2188 When perl begins to parse any block construct that provides a lexical scope
2189 (e.g., eval body, required file, subroutine body, loop body, or conditional
2190 block), the existing value of C<$^H> is saved, but its value is left unchanged.
2191 When the compilation of the block is completed, it regains the saved value.
2192 Between the points where its value is saved and restored, code that
2193 executes within BEGIN blocks is free to change the value of C<$^H>.
2195 This behavior provides the semantic of lexical scoping, and is used in,
2196 for instance, the C<use strict> pragma.
2198 The contents should be an integer; different bits of it are used for
2199 different pragmatic flags. Here's an example:
2201 sub add_100 { $^H |= 0x100 }
2208 Consider what happens during execution of the BEGIN block. At this point
2209 the BEGIN block has already been compiled, but the body of C<foo()> is still
2210 being compiled. The new value of C<$^H>
2211 will therefore be visible only while
2212 the body of C<foo()> is being compiled.
2214 Substitution of C<BEGIN { add_100() }> block with:
2216 BEGIN { require strict; strict->import('vars') }
2218 demonstrates how C<use strict 'vars'> is implemented. Here's a conditional
2219 version of the same lexical pragma:
2222 require strict; strict->import('vars') if $condition
2225 This variable was added in Perl 5.003.
2230 The C<%^H> hash provides the same scoping semantic as C<$^H>. This makes
2231 it useful for implementation of lexically scoped pragmas. See
2232 L<perlpragma>. All the entries are stringified when accessed at
2233 runtime, so only simple values can be accommodated. This means no
2234 pointers to objects, for example.
2236 When putting items into C<%^H>, in order to avoid conflicting with other
2237 users of the hash there is a convention regarding which keys to use.
2238 A module should use only keys that begin with the module's name (the
2239 name of its main package) and a "/" character. For example, a module
2240 C<Foo::Bar> should use keys such as C<Foo::Bar/baz>.
2242 This variable was added in Perl v5.6.0.
2247 An internal variable used by PerlIO. A string in two parts, separated
2248 by a C<\0> byte, the first part describes the input layers, the second
2249 part describes the output layers.
2251 This variable was added in Perl v5.8.0.
2258 The internal variable for debugging support. The meanings of the
2259 various bits are subject to change, but currently indicate:
2265 Debug subroutine enter/exit.
2269 Line-by-line debugging. Causes C<DB::DB()> subroutine to be called for
2270 each statement executed. Also causes saving source code lines (like
2275 Switch off optimizations.
2279 Preserve more data for future interactive inspections.
2283 Keep info about source lines on which a subroutine is defined.
2287 Start with single-step on.
2291 Use subroutine address instead of name when reporting.
2295 Report C<goto &subroutine> as well.
2299 Provide informative "file" names for evals based on the place they were compiled.
2303 Provide informative names to anonymous subroutines based on the place they
2308 Save source code lines into C<@{"_<$filename"}>.
2312 When saving source, include evals that generate no subroutines.
2316 When saving source, include source that did not compile.
2320 Some bits may be relevant at compile-time only, some at
2321 run-time only. This is a new mechanism and the details may change.
2322 See also L<perldebguts>.
2327 Reflects if taint mode is on or off. 1 for on (the program was run with
2328 B<-T>), 0 for off, -1 when only taint warnings are enabled (i.e. with
2331 This variable is read-only.
2333 This variable was added in Perl v5.8.0.
2335 =item ${^SAFE_LOCALES}
2338 Reflects if safe locale operations are available to this perl (when the
2339 value is 1) or not (the value is 0). This variable is always 1 if the
2340 perl has been compiled without threads. It is also 1 if this perl is
2341 using thread-safe locale operations. Note that an individual thread may
2342 choose to use the global locale (generally unsafe) by calling
2343 L<perlapi/switch_to_global_locale>. This variable currently is still
2344 set to 1 in such threads.
2346 This variable is read-only.
2348 This variable was added in Perl v5.28.0.
2353 Reflects certain Unicode settings of Perl. See L<perlrun>
2354 documentation for the C<-C> switch for more information about
2355 the possible values.
2357 This variable is set during Perl startup and is thereafter read-only.
2359 This variable was added in Perl v5.8.2.
2364 This variable controls the state of the internal UTF-8 offset caching code.
2365 1 for on (the default), 0 for off, -1 to debug the caching code by checking
2366 all its results against linear scans, and panicking on any discrepancy.
2368 This variable was added in Perl v5.8.9. It is subject to change or
2369 removal without notice, but is currently used to avoid recalculating the
2370 boundaries of multi-byte UTF-8-encoded characters.
2372 =item ${^UTF8LOCALE}
2375 This variable indicates whether a UTF-8 locale was detected by perl at
2376 startup. This information is used by perl when it's in
2377 adjust-utf8ness-to-locale mode (as when run with the C<-CL> command-line
2378 switch); see L<perlrun> for more info on this.
2380 This variable was added in Perl v5.8.8.
2384 =head2 Deprecated and removed variables
2386 Deprecating a variable announces the intent of the perl maintainers to
2387 eventually remove the variable from the language. It may still be
2388 available despite its status. Using a deprecated variable triggers
2391 Once a variable is removed, its use triggers an error telling you
2392 the variable is unsupported.
2394 See L<perldiag> for details about error messages.
2401 C<$#> was a variable that could be used to format printed numbers.
2402 After a deprecation cycle, its magic was removed in Perl v5.10.0 and
2403 using it now triggers a warning: C<$# is no longer supported>.
2405 This is not the sigil you use in front of an array name to get the
2406 last index, like C<$#array>. That's still how you get the last index
2407 of an array in Perl. The two have nothing to do with each other.
2409 Deprecated in Perl 5.
2411 Removed in Perl v5.10.0.
2416 C<$*> was a variable that you could use to enable multiline matching.
2417 After a deprecation cycle, its magic was removed in Perl v5.10.0.
2418 Using it now triggers a warning: C<$* is no longer supported>.
2419 You should use the C</s> and C</m> regexp modifiers instead.
2421 Deprecated in Perl 5.
2423 Removed in Perl v5.10.0.
2428 This variable stores the index of the first element in an array, and
2429 of the first character in a substring. The default is 0, but you could
2430 theoretically set it to 1 to make Perl behave more like B<awk> (or Fortran)
2431 when subscripting and when evaluating the index() and substr() functions.
2433 As of release 5 of Perl, assignment to C<$[> is treated as a compiler
2434 directive, and cannot influence the behavior of any other file.
2435 (That's why you can only assign compile-time constants to it.)
2436 Its use is highly discouraged.
2438 Prior to Perl v5.10.0, assignment to C<$[> could be seen from outer lexical
2439 scopes in the same file, unlike other compile-time directives (such as
2440 L<strict>). Using local() on it would bind its value strictly to a lexical
2441 block. Now it is always lexically scoped.
2443 As of Perl v5.16.0, it is implemented by the L<arybase> module.
2445 As of Perl v5.30.0, or under C<use v5.16>, or C<no feature "array_base">,
2446 C<$[> no longer has any effect, and always contains 0.
2447 Assigning 0 to it is permitted, but any other value will produce an error.
2449 Mnemonic: [ begins subscripts.
2451 Deprecated in Perl v5.12.0.