=back
+As C<$_> is a global variable, this may lead in some cases to unwanted
+side-effects. As of perl 5.9.1, you can now use a lexical version of
+C<$_> by declaring it in a file or in a block with C<my>. Moreover,
+declaring C<our $> restores the global C<$_> in the current scope.
+
(Mnemonic: underline is understood in certain operations.)
=back
Special package variables when using sort(), see L<perlfunc/sort>.
Because of this specialness $a and $b don't need to be declared
-(using local(), use vars, or our()) even when using the strict
-vars pragma. Don't lexicalize them with C<my $a> or C<my $b>
-if you want to be able to use them in the sort() comparison block
-or function.
+(using use vars, or our()) even when using the C<strict 'vars'> pragma.
+Don't lexicalize them with C<my $a> or C<my $b> if you want to be
+able to use them in the sort() comparison block or function.
=back
how many subgroups were in the last successful match. See the
examples given for the C<@-> variable.
-=item $MULTILINE_MATCHING
-
-=item $*
-
-Set to a non-zero integer value to do multi-line matching within a
-string, 0 (or undefined) to tell Perl that it can assume that strings
-contain a single line, for the purpose of optimizing pattern matches.
-Pattern matches on strings containing multiple newlines can produce
-confusing results when C<$*> is 0 or undefined. Default is undefined.
-(Mnemonic: * matches multiple things.) This variable influences the
-interpretation of only C<^> and C<$>. A literal newline can be searched
-for even when C<$* == 0>.
-
-Use of C<$*> is deprecated in modern Perl, supplanted by
-the C</s> and C</m> modifiers on pattern matching.
-
-Assigning a non-numerical value to C<$*> triggers a warning (and makes
-C<$*> act if C<$* == 0>), while assigning a numerical value to C<$*>
-makes that an implicit C<int> is applied on the value.
-
=item HANDLE->input_line_number(EXPR)
=item $INPUT_LINE_NUMBER
not reading from a record-oriented file (or your OS doesn't have
record-oriented files), then you'll likely get a full chunk of data
with every read. If a record is larger than the record size you've
-set, you'll get the record back in pieces.
+set, you'll get the record back in pieces. Trying to set the record
+size to zero or less will cause reading in the (rest of the) whole file.
On VMS, record reads are done with the equivalent of C<sysread>,
so it's best not to mix record and non-record reads on the same
=item $,
-The output field separator for the print operator. Ordinarily the
-print operator simply prints out its arguments without further
-adornment. To get behavior more like B<awk>, set this variable as
-you would set B<awk>'s OFS variable to specify what is printed
-between fields. (Mnemonic: what is printed when there is a "," in
-your print statement.)
+The output field separator for the print operator. If defined, this
+value is printed between each of print's arguments. Default is C<undef>.
+(Mnemonic: what is printed when there is a "," in your print statement.)
=item IO::Handle->output_record_separator EXPR
=item $\
-The output record separator for the print operator. Ordinarily the
-print operator simply prints out its arguments as is, with no
-trailing newline or other end-of-record string added. To get
-behavior more like B<awk>, set this variable as you would set
-B<awk>'s ORS variable to specify what is printed at the end of the
-print. (Mnemonic: you set C<$\> instead of adding "\n" at the
-end of the print. Also, it's just like C<$/>, but it's what you
-get "back" from Perl.)
+The output record separator for the print operator. If defined, this
+value is printed after the last of print's arguments. Default is C<undef>.
+(Mnemonic: you set C<$\> instead of adding "\n" at the end of the print.
+Also, it's just like C<$/>, but it's what you get "back" from Perl.)
=item $LIST_SEPARATOR
Consider using "real" multidimensional arrays as described
in L<perllol>.
-=item $OFMT
-
-=item $#
-
-The output format for printed numbers. This variable is a half-hearted
-attempt to emulate B<awk>'s OFMT variable. There are times, however,
-when B<awk> and Perl have differing notions of what counts as
-numeric. The initial value is "%.I<n>g", where I<n> is the value
-of the macro DBL_DIG from your system's F<float.h>. This is different from
-B<awk>'s default OFMT setting of "%.6g", so you need to set C<$#>
-explicitly to get B<awk>'s value. (Mnemonic: # is the number sign.)
-
-Use of C<$#> is deprecated.
-
=item HANDLE->format_page_number(EXPR)
=item $FORMAT_PAGE_NUMBER
I<n>-th subpattern, or undef if the subpattern did not match.
Thus after a match against $_, $& coincides with C<substr $_, $-[0],
-$+[0] - $-[0]>. Similarly, C<$>I<n> coincides with C<substr $_, $-[>I<n>C<],
-$+[>I<n>C<] - $-[>I<n>C<]> if C<$-[>I<n>C<]> is defined, and $+ coincides with
-C<substr $_, $-[$#-], $+[$#-]>. One can use C<$#-> to find the last
+$+[0] - $-[0]>. Similarly, $I<n> coincides with C<substr $_, $-[n],
+$+[n] - $-[n]> if C<$-[n]> is defined, and $+ coincides with
+C<substr $_, $-[$#-], $+[$#-] - $-[$#-]>. One can use C<$#-> to find the last
matched subgroup in the last successful match. Contrast with
C<$#+>, the number of subgroups in the regular expression. Compare
with C<@+>.
=item C<$2> is the same as C<substr($var, $-[2], $+[2] - $-[2])>
-=item C<$3> is the same as C<substr $var, $-[3], $+[3] - $-[3])>
+=item C<$3> is the same as C<substr($var, $-[3], $+[3] - $-[3])>
=back
The status returned by the last pipe close, backtick (C<``>) command,
successful call to wait() or waitpid(), or from the system()
operator. This is just the 16-bit status word returned by the
-wait() system call (or else is made up to look like it). Thus, the
+traditional Unix wait() system call (or else is made up to look like it). Thus, the
exit value of the subprocess is really (C<<< $? >> 8 >>>), and
C<$? & 127> gives which signal, if any, the process died from, and
C<$? & 128> reports whether there was a core dump. (Mnemonic:
Also see L<Error Indicators>.
+=item ${^CHILD_ERROR_NATIVE}
+
+The native status returned by the last pipe close, backtick (C<``>)
+command, successful call to wait() or waitpid(), or from the system()
+operator. On POSIX-like systems this value can be decoded with the
+WIFEXITED, WEXITSTATUS, WIFSIGNALED, WTERMSIG, WIFSTOPPED, WSTOPSIG
+and WIFCONTINUED functions provided by the L<POSIX> module.
+
+Under VMS this reflects the actual VMS exit status; i.e. it is the same
+as $? when the pragma C<use vmsish 'status'> is in effect.
+
=item ${^ENCODING}
The I<object reference> to the Encode object that is used to convert
C<undef>. A successful system or library call does B<not> set
the variable to zero.
-If used an a string, yields the corresponding system error string.
+If used as a string, yields the corresponding system error string.
You can assign a number to C<$!> to set I<errno> if, for instance,
you want C<"$!"> to return the string for error I<n>, or you want
to set the exit value for the die() operator. (Mnemonic: What just
consider this variable read-only, although it will be altered
across fork() calls. (Mnemonic: same as shells.)
+Note for Linux users: on Linux, the C functions C<getpid()> and
+C<getppid()> return different values from different threads. In order to
+be portable, this behavior is not reflected by C<$$>, whose value remains
+consistent across threads. If you want to call the underlying C<getpid()>,
+you may use the CPAN module C<Linux::Pid>.
+
=item $REAL_USER_ID
=item $UID
The real uid of this process. (Mnemonic: it's the uid you came I<from>,
if you're running setuid.) You can change both the real uid and
-the effective uid at the same time by using POSIX::setuid().
+the effective uid at the same time by using POSIX::setuid(). Since
+changes to $< require a system call, check $! after a change attempt to
+detect any possible errors.
=item $EFFECTIVE_USER_ID
($<,$>) = ($>,$<); # swap real and effective uid
You can change both the effective uid and the real uid at the same
-time by using POSIX::setuid().
+time by using POSIX::setuid(). Changes to $> require a check to $!
+to detect any possible errors after an attempted change.
(Mnemonic: it's the uid you went I<to>, if you're running setuid.)
C<< $< >> and C<< $> >> can be swapped only on machines
back to C<$(> without being forced numeric, such as by adding zero.
You can change both the real gid and the effective gid at the same
-time by using POSIX::setgid().
+time by using POSIX::setgid(). Changes to $( require a check to $!
+to detect any possible errors after an attempted change.
(Mnemonic: parentheses are used to I<group> things. The real gid is the
group you I<left>, if you're running setgid.)
You can change both the effective gid and the real gid at the same
time by using POSIX::setgid() (use only a single numeric argument).
+Changes to $) require a check to $! to detect any possible errors
+after an attempted change.
(Mnemonic: parentheses are used to I<group> things. The effective gid
is the group that's I<right> for you, if you're running setgid.)
=item $0
-Contains the name of the program being executed. On some operating
-systems assigning to C<$0> modifies the argument area that the B<ps>
-program sees. This is more useful as a way of indicating the current
-program state than it is for hiding the program you're running.
-(Mnemonic: same as B<sh> and B<ksh>.)
+Contains the name of the program being executed.
+
+On some (read: not all) operating systems assigning to C<$0> modifies
+the argument area that the C<ps> program sees. On some platforms you
+may have to use special C<ps> options or a different C<ps> to see the
+changes. Modifying the $0 is more useful as a way of indicating the
+current program state than it is for hiding the program you're
+running. (Mnemonic: same as B<sh> and B<ksh>.)
+
+Note that there are platform specific limitations on the maximum
+length of C<$0>. In the most extreme case it may be limited to the
+space occupied by the original C<$0>.
+
+In some platforms there may be arbitrary amount of padding, for
+example space characters, after the modified name as shown by C<ps>.
+In some platforms this padding may extend all the way to the original
+length of the argument area, no matter what you do (this is the case
+for example with Linux 2.2).
Note for BSD users: setting C<$0> does not completely remove "perl"
-from the ps(1) output. For example, setting C<$0> to C<"foobar"> will
-result in C<"perl: foobar (perl)">. This is an operating system
-feature.
+from the ps(1) output. For example, setting C<$0> to C<"foobar"> may
+result in C<"perl: foobar (perl)"> (whether both the C<"perl: "> prefix
+and the " (perl)" suffix are shown depends on your exact BSD variant
+and version). This is an operating system feature, Perl cannot help it.
+
+In multithreaded scripts Perl coordinates the threads so that any
+thread may modify its copy of the C<$0> and the change becomes visible
+to ps(1) (assuming the operating system plays along). Note that
+the view of C<$0> the other threads have will not change since they
+have their own copies of it.
=item $[
As of release 5 of Perl, assignment to C<$[> is treated as a compiler
directive, and cannot influence the behavior of any other file.
+(That's why you can only assign compile-time constants to it.)
Its use is highly discouraged.
+Note that, unlike other compile-time directives (such as L<strict>),
+assignment to C<$[> can be seen from outer lexical scopes in the same file.
+However, you can use local() on it to strictly bind its value to a
+lexical block.
+
=item $]
The version + patchlevel / 1000 of the Perl interpreter. This variable
=item $^D
The current value of the debugging flags. (Mnemonic: value of B<-D>
-switch.)
+switch.) May be read or set. Like its command-line equivalent, you can use
+numeric or symbolic values, eg C<$^D = 10> or C<$^D = "st">.
+
+=item ${^RE_DEBUG_FLAGS}
+
+The current value of the regex debugging flags. Set to 0 for no debug output
+even when the re 'debug' module is loaded. See L<re> for details.
+
+=item ${^RE_TRIE_MAXBUF}
+
+Controls how certain regex optimisations are applied and how much memory they
+utilize. This value by default is 65536 which corresponds to a 512kB temporary
+cache. Set this to a higher value to trade memory for speed when matching
+large alternations. Set it to a lower value if you want the optimisations to
+be as conservative of memory as possible but still occur, and set it to a
+negative value to prevent the optimisation and conserve the most memory.
+Under normal situations this variable should be of no interest to you.
=item $SYSTEM_FD_MAX
=item %^H
-WARNING: This variable is strictly for internal use only. Its availability,
-behavior, and contents are subject to change without notice.
-
The %^H hash provides the same scoping semantic as $^H. This makes it
-useful for implementation of lexically scoped pragmas.
+useful for implementation of lexically scoped pragmas. See L<perlpragma>.
=item $INPLACE_EDIT
By default, running out of memory is an untrappable, fatal error.
However, if suitably built, Perl can use the contents of C<$^M>
as an emergency memory pool after die()ing. Suppose that your Perl
-were compiled with -DPERL_EMERGENCY_SBRK and used Perl's malloc.
+were compiled with C<-DPERL_EMERGENCY_SBRK> and used Perl's malloc.
Then
$^M = 'a' x (1 << 16);
would allocate a 64K buffer for use in an emergency. See the
F<INSTALL> file in the Perl distribution for information on how to
-enable this option. To discourage casual use of this advanced
-feature, there is no L<English|English> long name for this variable.
+add custom C compilation flags when compiling perl. To discourage casual
+use of this advanced feature, there is no L<English|English> long name for
+this variable.
=item $OSNAME
B<-V> command-line switch documented in L<perlrun>.
In Windows platforms, $^O is not very helpful: since it is always
-C<MSWin32>, it doesn't tell the difference between 95/98/ME/NT/2000/XP/CE.
-Use Win32::GetOSVersion() (see L<perlport>) and other means (like for
-example the presence/absence of some files) to distinguish between
-the variants.
+C<MSWin32>, it doesn't tell the difference between
+95/98/ME/NT/2000/XP/CE/.NET. Use Win32::GetOSName() or
+Win32::GetOSVersion() (see L<Win32> and L<perlport>) to distinguish
+between the variants.
=item ${^OPEN}
An internal variable used by PerlIO. A string in two parts, separated
-by a C<\0> byte, the first part is the input disciplines, the second
-part is the output disciplines.
+by a C<\0> byte, the first part describes the input layers, the second
+part describes the output layers.
=item $PERLDB
Provide informative names to anonymous subroutines based on the place they
were compiled.
+=item 0x400
+
+Debug assertion subroutines enter/exit.
+
=back
Some bits may be relevant at compile-time only, some at
=item $^S
-Current state of the interpreter. Undefined if parsing of the current
-module/eval is not finished (may happen in $SIG{__DIE__} and
-$SIG{__WARN__} handlers). True if inside an eval(), otherwise false.
+Current state of the interpreter.
+
+ $^S State
+ --------- -------------------
+ undef Parsing module/eval
+ true (1) Executing an eval
+ false (0) Otherwise
+
+The first state may happen in $SIG{__DIE__} and $SIG{__WARN__} handlers.
=item $BASETIME
=item ${^TAINT}
-Reflects if taint mode is on or off (i.e. if the program was run with
-B<-T> or not). True for on, false for off.
+Reflects if taint mode is on or off. 1 for on (the program was run with
+B<-T>), 0 for off, -1 when only taint warnings are enabled (i.e. with
+B<-t> or B<-TU>). This variable is read-only.
+
+=item ${^UNICODE}
+
+Reflects certain Unicode settings of Perl. See L<perlrun>
+documentation for the C<-C> switch for more information about
+the possible values. This variable is set during Perl startup
+and is thereafter read-only.
+
+=item ${^UTF8CACHE}
+
+This variable controls the state of the internal UTF-8 offset caching code.
+1 for on (the default), 0 for off, -1 to debug the caching code by checking
+all its results against linear scans, and panicking on any discrepancy.
+
+=item ${^UTF8LOCALE}
+
+This variable indicates whether an UTF-8 locale was detected by perl at
+startup. This information is used by perl when it's in
+adjust-utf8ness-to-locale mode (as when run with the C<-CL> command-line
+switch); see L<perlrun> for more info on this.
=item $PERL_VERSION
C<$^V eq v5.6.0>. Note that the characters in this string value can
potentially be in Unicode range.
+This variable first appeared in perl 5.6.0; earlier versions of perl will
+see an undefined value.
+
This can be used to determine whether the Perl interpreter executing a
script is in the right range of versions. (Mnemonic: use ^V for Version
Control.) Example:
- warn "No \"our\" declarations!\n" if $^V and $^V lt v5.6.0;
+ warn "Hashes not randomized!\n" if !$^V or $^V lt v5.8.1
To convert C<$^V> into its string representation use sprintf()'s
C<"%vd"> conversion:
The current set of warning checks enabled by the C<use warnings> pragma.
See the documentation of C<warnings> for more details.
-=item ${^WIDE_SYSTEM_CALLS}
+=item ${^WIN32_SLOPPY_STAT}
-Global flag that enables system calls made by Perl to use wide character
-APIs native to the system, if available. This is currently only implemented
-on the Windows platform.
+If this variable is set to a true value, then stat() on Windows will
+not try to open the file. This means that the link count cannot be
+determined and file attributes may be out of date if additional
+hardlinks to the file exist. On the other hand, not opening the file
+is considerably faster, especially for files on network drives.
-This can also be enabled from the command line using the C<-C> switch.
-
-The initial value is typically C<0> for compatibility with Perl versions
-earlier than 5.6, but may be automatically set to C<1> by Perl if the system
-provides a user-settable default (e.g., C<$ENV{LC_CTYPE}>).
-
-The C<bytes> pragma always overrides the effect of this flag in the current
-lexical scope. See L<bytes>.
+This variable could be set in the F<sitecustomize.pl> file to
+configure the local Perl installation to use "sloppy" stat() by
+default. See L<perlrun> for more information about site
+customization.
=item $EXECUTABLE_NAME
=item $^X
The name used to execute the current copy of Perl, from C's
-C<argv[0]>.
+C<argv[0]> or (where supported) F</proc/self/exe>.
Depending on the host operating system, the value of $^X may be
a relative or absolute pathname of the perl program file, or may
a command. To convert the value of $^X to a path name, use the
following statements:
-# Build up a set of file names (not command names).
+ # Build up a set of file names (not command names).
use Config;
$this_perl = $^X;
if ($^O ne 'VMS')
one, because C<$ARGV[0]> is the first argument, I<not> the program's
command name itself. See C<$0> for the command name.
+=item ARGVOUT
+
+The special filehandle that points to the currently open output file
+when doing edit-in-place processing with B<-i>. Useful when you have
+to do a lot of inserting and don't want to keep modifying $_. See
+L<perlrun> for the B<-i> switch.
+
=item @F
The array @F contains the fields of each line read in when autosplit
code directly into @INC. Those hooks may be subroutine references, array
references or blessed objects. See L<perlfunc/require> for details.
+=item @ARG
+
=item @_
Within a subroutine the array @_ contains the parameters passed to that
lest you inadvertently call it.
If your system has the sigaction() function then signal handlers are
-installed using it. This means you get reliable signal handling. If
-your system has the SA_RESTART flag it is used when signals handlers are
-installed. This means that system calls for which restarting is supported
-continue rather than returning when a signal arrives. If you want your
-system calls to be interrupted by signal delivery then do something like
-this:
-
- use POSIX ':signal_h';
-
- my $alarm = 0;
- sigaction SIGALRM, new POSIX::SigAction sub { $alarm = 1 }
- or die "Error setting SIGALRM handler: $!\n";
+installed using it. This means you get reliable signal handling.
-See L<POSIX>.
+The default delivery policy of signals changed in Perl 5.8.0 from
+immediate (also known as "unsafe") to deferred, also known as
+"safe signals". See L<perlipc> for more information.
Certain internal hooks can be also set using the %SIG hash. The
routine indicated by C<$SIG{__WARN__}> is called when a warning message is
may happen if C<open> or C<close> were imported with bad prototypes),
or if Perl code executed during evaluation die()d . In these cases
the value of $@ is the compile error, or the argument to C<die>
-(which will interpolate C<$!> and C<$?>!). (See also L<Fatal>,
+(which will interpolate C<$!> and C<$?>). (See also L<Fatal>,
though.)
When the eval() expression above is executed, open(), C<< <PIPE> >>,
Perl identifiers that begin with digits, control characters, or
punctuation characters are exempt from the effects of the C<package>
-declaration and are always forced to be in package C<main>. A few
-other names are also exempt:
+declaration and are always forced to be in package C<main>; they are
+also exempt from C<strict 'vars'> errors. A few other names are also
+exempt in these ways:
ENV STDIN
INC STDOUT
ARGV STDERR
- ARGVOUT
+ ARGVOUT _
SIG
In particular, the new special C<${^_XYZ}> variables are always taken
to be in package C<main>, regardless of any C<package> declarations
-presently in scope.
+presently in scope.
=head1 BUGS
https://perl5.git.perl.org / perl5.git / blobdiff