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-=head1 NAME
-
-perlvar - Perl predefined variables
-
-=head1 DESCRIPTION
-
-=head2 The Syntax of Variable Names
-
-Variable names in Perl can have several formats. Usually, they
-must begin with a letter or underscore, in which case they can be
-arbitrarily long (up to an internal limit of 251 characters) and
-may contain letters, digits, underscores, or the special sequence
-C<::> or C<'>. In this case, the part before the last C<::> or
-C<'> is taken to be a I<package qualifier>; see L<perlmod>.
-
-Perl variable names may also be a sequence of digits or a single
-punctuation or control character. These names are all reserved for
-special uses by Perl; for example, the all-digits names are used
-to hold data captured by backreferences after a regular expression
-match. Perl has a special syntax for the single-control-character
-names: It understands C<^X> (caret C<X>) to mean the control-C<X>
-character. For example, the notation C<$^W> (dollar-sign caret
-C<W>) is the scalar variable whose name is the single character
-control-C<W>. This is better than typing a literal control-C<W>
-into your program.
-
-Since Perl 5.6, Perl variable names may be alphanumeric
-strings that begin with control characters (or better yet, a caret).
-These variables must be written in the form C<${^Foo}>; the braces
-are not optional. C<${^Foo}> denotes the scalar variable whose
-name is a control-C<F> followed by two C<o>'s. These variables are
-reserved for future special uses by Perl, except for the ones that
-begin with C<^_> (control-underscore or caret-underscore). No
-control-character name that begins with C<^_> will acquire a special
-meaning in any future version of Perl; such names may therefore be
-used safely in programs. C<$^_> itself, however, I<is> reserved.
-
-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>; 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
- SIG
-
-In particular, the special C<${^_XYZ}> variables are always taken
-to be in package C<main>, regardless of any C<package> declarations
-presently in scope.
-
-=head1 SPECIAL VARIABLES
-
-The following names have special meaning to Perl. Most punctuation
-names have reasonable mnemonics, or analogs in the shells.
-Nevertheless, if you wish to use long variable names, you need only say:
-
- use English;
-
-at the top of your program. This aliases all the short names to the long
-names in the current package. Some even have medium names, generally
-borrowed from B<awk>. To avoid a performance hit, if you don't need the
-C<$PREMATCH>, C<$MATCH>, or C<$POSTMATCH> it's best to use the C<English>
-module without them:
-
- use English '-no_match_vars';
-
-Before you continue, note the sort order for variables. In general, we
-first list the variables in case-insensitive, almost-lexigraphical
-order (ignoring the C<{> or C<^> preceding words, as in C<${^UNICODE}>
-or C<$^T>), although C<$_> and C<@_> move up to the top of the pile.
-For variables with the same identifier, we list it in order of scalar,
-array, hash, and bareword.
-
-=head2 General Variables
-
-=over 8
-
-=item $ARG
-
-=item $_
-X<$_> X<$ARG>
-
-The default input and pattern-searching space. The following pairs are
-equivalent:
-
- while (<>) {...} # equivalent only in while!
- while (defined($_ = <>)) {...}
-
- /^Subject:/
- $_ =~ /^Subject:/
-
- tr/a-z/A-Z/
- $_ =~ tr/a-z/A-Z/
-
- chomp
- chomp($_)
-
-Here are the places where Perl will assume C<$_> even if you don't use it:
-
-=over 3
-
-=item *
-
-The following functions use C<$_> as a default argument:
-
-abs, alarm, chomp, chop, chr, chroot,
-cos, defined, eval, evalbytes, exp, glob,
-hex, int, lc, lcfirst, length, log, lstat, mkdir, oct, ord, pos, print,
-quotemeta, readlink, readpipe, ref, require, reverse (in scalar context only),
-rmdir, sin, split (on its second argument), sqrt, stat, study, uc, ucfirst,
-unlink, unpack.
-
-=item *
-
-All file tests (C<-f>, C<-d>) except for C<-t>, which defaults to STDIN.
-See L<perlfunc/-X>
-
-=item *
-
-The pattern matching operations C<m//>, C<s///> and C<tr///> (aka C<y///>)
-when used without an C<=~> operator.
-
-=item *
-
-The default iterator variable in a C<foreach> loop if no other
-variable is supplied.
-
-=item *
-
-The implicit iterator variable in the C<grep()> and C<map()> functions.
-
-=item *
-
-The implicit variable of C<given()>.
-
-=item *
-
-The default place to put an input record when a C<< <FH> >>
-operation's result is tested by itself as the sole criterion of a C<while>
-test. Outside a C<while> test, this will not happen.
-
-=back
-
-As C<$_> is a global variable, this may lead in some cases to unwanted
-side-effects. As of perl 5.10, you can now use a lexical version of
-C<$_> 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.
-
-=item @ARG
-
-=item @_
-X<@_> X<@ARG>
-
-Within a subroutine the array C<@_> contains the parameters passed to
-that subroutine. Inside a subroutine, C<@_> is the default array for
-the array operators C<push>, C<pop>, C<shift>, and C<unshift>.
-
-See L<perlsub>.
-
-=item $LIST_SEPARATOR
-
-=item $"
-X<$"> X<$LIST_SEPARATOR>
-
-When an array or an array slice is interpolated into a double-quoted
-string or a similar context such as C</.../>, its elements are
-separated by this value. Default is a space. For example, this:
-
- print "The array is: @array\n";
-
-is equivalent to this:
-
- print "The array is: " . join($", @array) . "\n";
-
-Mnemonic: works in double-quoted context.
-
-=item $PROCESS_ID
-
-=item $PID
-
-=item $$
-X<$$> X<$PID> X<$PROCESS_ID>
-
-The process number of the Perl running this script. Though you I<can> set
-this variable, doing so is generally discouraged, although it can be
-invaluable for some testing purposes. It will be reset automatically
-across C<fork()> calls.
-
-Note for Linux and Debian GNU/kFreeBSD users: Before Perl v5.16.0 perl
-would emulate POSIX semantics on Linux systems using LinuxThreads, a
-partial implementation of POSIX Threads that has since been superseded
-by the Native POSIX Thread Library (NPTL).
-
-LinuxThreads is now obsolete on Linux, and and caching C<getpid()>
-like this made embedding perl unnecessarily complex (since you'd have
-to manually update the value of $$), so now C<$$> and C<getppid()>
-will always return the same values as the underlying C library.
-
-Debian GNU/kFreeBSD systems also used LinuxThreads up until and
-including the 6.0 release, but after that moved to FreeBSD thread
-semantics, which are POSIX-like.
-
-To see if your system is affected by this discrepancy check if
-C<getconf GNU_LIBPTHREAD_VERSION | grep -q NPTL> returns a false
-value. NTPL threads preserve the POSIX semantics.
-
-Mnemonic: same as shells.
-
-=item $PROGRAM_NAME
-
-=item $0
-X<$0> X<$PROGRAM_NAME>
-
-Contains the name of the program being executed.
-
-On some (but 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 C<$0> is more useful as a way of indicating the
-current program state than it is for hiding the program you're
-running.
-
-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"> 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.
-
-If the program has been given to perl via the switches C<-e> or C<-E>,
-C<$0> will contain the string C<"-e">.
-
-On Linux as of perl 5.14 the legacy process name will be set with
-C<prctl(2)>, in addition to altering the POSIX name via C<argv[0]> as
-perl has done since version 4.000. Now system utilities that read the
-legacy process name such as ps, top and killall will recognize the
-name you set when assigning to C<$0>. The string you supply will be
-cut off at 16 bytes, this is a limitation imposed by Linux.
-
-Mnemonic: same as B<sh> and B<ksh>.
-
-=item $REAL_GROUP_ID
-
-=item $GID
-
-=item $(
-X<$(> X<$GID> X<$REAL_GROUP_ID>
-
-The real gid of this process. If you are on a machine that supports
-membership in multiple groups simultaneously, gives a space separated
-list of groups you are in. The first number is the one returned by
-C<getgid()>, and the subsequent ones by C<getgroups()>, one of which may be
-the same as the first number.
-
-However, a value assigned to C<$(> must be a single number used to
-set the real gid. So the value given by C<$(> should I<not> be assigned
-back to C<$(> without being forced numeric, such as by adding zero. Note
-that this is different to the effective gid (C<$)>) which does take a
-list.
-
-You can change both the real gid and the effective gid at the same
-time by using C<POSIX::setgid()>. Changes
-to C<$(> require a check to C<$!>
-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.
-
-=item $EFFECTIVE_GROUP_ID
-
-=item $EGID
-
-=item $)
-X<$)> X<$EGID> X<$EFFECTIVE_GROUP_ID>
-
-The effective gid of this process. If you are on a machine that
-supports membership in multiple groups simultaneously, gives a space
-separated list of groups you are in. The first number is the one
-returned by C<getegid()>, and the subsequent ones by C<getgroups()>,
-one of which may be the same as the first number.
-
-Similarly, a value assigned to C<$)> must also be a space-separated
-list of numbers. The first number sets the effective gid, and
-the rest (if any) are passed to C<setgroups()>. To get the effect of an
-empty list for C<setgroups()>, just repeat the new effective gid; that is,
-to force an effective gid of 5 and an effectively empty C<setgroups()>
-list, say C< $) = "5 5" >.
-
-You can change both the effective gid and the real gid at the same
-time by using C<POSIX::setgid()> (use only a single numeric argument).
-Changes to C<$)> require a check to C<$!> to detect any possible errors
-after an attempted change.
-
-C<< $< >>, C<< $> >>, C<$(> and C<$)> can be set only on
-machines that support the corresponding I<set[re][ug]id()> routine. C<$(>
-and C<$)> can be swapped only on machines supporting C<setregid()>.
-
-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 $REAL_USER_ID
-
-=item $UID
-
-=item $<
-X<< $< >> X<$UID> X<$REAL_USER_ID>
-
-The real uid of this process. You can change both the real uid and the
-effective uid at the same time by using C<POSIX::setuid()>. Since
-changes to C<< $< >> require a system call, check C<$!> after a change
-attempt to detect any possible errors.
-
-Mnemonic: it's the uid you came I<from>, if you're running setuid.
-
-=item $EFFECTIVE_USER_ID
-
-=item $EUID
-
-=item $>
-X<< $> >> X<$EUID> X<$EFFECTIVE_USER_ID>
-
-The effective uid of this process. For example:
-
- $< = $>; # set real to effective uid
- ($<,$>) = ($>,$<); # swap real and effective uids
-
-You can change both the effective uid and the real uid at the same
-time by using C<POSIX::setuid()>. Changes to C<< $> >> require a check
-to C<$!> to detect any possible errors after an attempted change.
-
-C<< $< >> and C<< $> >> can be swapped only on machines
-supporting C<setreuid()>.
-
-Mnemonic: it's the uid you went I<to>, if you're running setuid.
-
-=item $SUBSCRIPT_SEPARATOR
-
-=item $SUBSEP
-
-=item $;
-X<$;> X<$SUBSEP> X<SUBSCRIPT_SEPARATOR>
-
-The subscript separator for multidimensional array emulation. If you
-refer to a hash element as
-
- $foo{$a,$b,$c}
-
-it really means
-
- $foo{join($;, $a, $b, $c)}
-
-But don't put
-
- @foo{$a,$b,$c} # a slice--note the @
-
-which means
-
- ($foo{$a},$foo{$b},$foo{$c})
-
-Default is "\034", the same as SUBSEP in B<awk>. If your keys contain
-binary data there might not be any safe value for C<$;>.
-
-Consider using "real" multidimensional arrays as described
-in L<perllol>.
-
-Mnemonic: comma (the syntactic subscript separator) is a semi-semicolon.
-
-=item $a
-
-=item $b
-X<$a> X<$b>
-
-Special package variables when using C<sort()>, see L<perlfunc/sort>.
-Because of this specialness C<$a> and C<$b> don't need to be declared
-(using C<use vars>, or C<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 C<sort()> comparison block or function.
-
-=item %ENV
-X<%ENV>
-
-The hash C<%ENV> contains your current environment. Setting a
-value in C<ENV> changes the environment for any child processes
-you subsequently C<fork()> off.
-
-=item $SYSTEM_FD_MAX
-
-=item $^F
-X<$^F> X<$SYSTEM_FD_MAX>
-
-The maximum system file descriptor, ordinarily 2. System file
-descriptors are passed to C<exec()>ed processes, while higher file
-descriptors are not. Also, during an
-C<open()>, system file descriptors are
-preserved even if the C<open()> fails (ordinary file descriptors are
-closed before the C<open()> is attempted). The close-on-exec
-status of a file descriptor will be decided according to the value of
-C<$^F> when the corresponding file, pipe, or socket was opened, not the
-time of the C<exec()>.
-
-=item @F
-X<@F>
-
-The array C<@F> contains the fields of each line read in when autosplit
-mode is turned on. See L<perlrun> for the B<-a> switch. This array
-is package-specific, and must be declared or given a full package name
-if not in package main when running under C<strict 'vars'>.
-
-=item @INC
-X<@INC>
-
-The array C<@INC> contains the list of places that the C<do EXPR>,
-C<require>, or C<use> constructs look for their library files. It
-initially consists of the arguments to any B<-I> command-line
-switches, followed by the default Perl library, probably
-F</usr/local/lib/perl>, followed by ".", to represent the current
-directory. ("." will not be appended if taint checks are enabled,
-either by C<-T> or by C<-t>.) If you need to modify this at runtime,
-you should use the C<use lib> pragma to get the machine-dependent
-library properly loaded also:
-
- use lib '/mypath/libdir/';
- use SomeMod;
-
-You can also insert hooks into the file inclusion system by putting Perl
-code directly into C<@INC>. Those hooks may be subroutine references,
-array references or blessed objects. See L<perlfunc/require> for details.
-
-=item %INC
-X<%INC>
-
-The hash C<%INC> contains entries for each filename included via the
-C<do>, C<require>, or C<use> operators. The key is the filename
-you specified (with module names converted to pathnames), and the
-value is the location of the file found. The C<require>
-operator uses this hash to determine whether a particular file has
-already been included.
-
-If the file was loaded via a hook (e.g. a subroutine reference, see
-L<perlfunc/require> for a description of these hooks), this hook is
-by default inserted into C<%INC> in place of a filename. Note, however,
-that the hook may have set the C<%INC> entry by itself to provide some more
-specific info.
-
-=item $INPLACE_EDIT
-
-=item $^I
-X<$^I> X<$INPLACE_EDIT>
-
-The current value of the inplace-edit extension. Use C<undef> to disable
-inplace editing.
-
-Mnemonic: value of B<-i> switch.
-
-=item $^M
-X<$^M>
-
-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 C<die()>ing. Suppose that your Perl
-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
-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.
-
-This variable was added in Perl 5.004.
-
-=item $OSNAME
-
-=item $^O
-X<$^O> X<$OSNAME>
-
-The name of the operating system under which this copy of Perl was
-built, as determined during the configuration process. For examples
-see L<perlport/PLATFORMS>.
-
-The value is identical to C<$Config{'osname'}>. See also L<Config>
-and the B<-V> command-line switch documented in L<perlrun>.
-
-In Windows platforms, C<$^O> is not very helpful: since it is always
-C<MSWin32>, it doesn't tell the difference between
-95/98/ME/NT/2000/XP/CE/.NET. Use C<Win32::GetOSName()> or
-Win32::GetOSVersion() (see L<Win32> and L<perlport>) to distinguish
-between the variants.
-
-This variable was added in Perl 5.003.
-
-=item %SIG
-X<%SIG>
-
-The hash C<%SIG> contains signal handlers for signals. For example:
-
- sub handler { # 1st argument is signal name
- my($sig) = @_;
- print "Caught a SIG$sig--shutting down\n";
- close(LOG);
- exit(0);
- }
-
- $SIG{'INT'} = \&handler;
- $SIG{'QUIT'} = \&handler;
- ...
- $SIG{'INT'} = 'DEFAULT'; # restore default action
- $SIG{'QUIT'} = 'IGNORE'; # ignore SIGQUIT
-
-Using a value of C<'IGNORE'> usually has the effect of ignoring the
-signal, except for the C<CHLD> signal. See L<perlipc> for more about
-this special case.
-
-Here are some other examples:
-
- $SIG{"PIPE"} = "Plumber"; # assumes main::Plumber (not
- # recommended)
- $SIG{"PIPE"} = \&Plumber; # just fine; assume current
- # Plumber
- $SIG{"PIPE"} = *Plumber; # somewhat esoteric
- $SIG{"PIPE"} = Plumber(); # oops, what did Plumber()
- # return??
-
-Be sure not to use a bareword as the name of a signal handler,
-lest you inadvertently call it.
-
-If your system has the C<sigaction()> function then signal handlers
-are installed using it. This means you get reliable signal handling.
-
-The default delivery policy of signals changed in Perl 5.8.0 from
-immediate (also known as "unsafe") to deferred, also known as "safe
-signals". See L<perlipc> for more information.
-
-Certain internal hooks can be also set using the C<%SIG> hash. The
-routine indicated by C<$SIG{__WARN__}> is called when a warning
-message is about to be printed. The warning message is passed as the
-first argument. The presence of a C<__WARN__> hook causes the
-ordinary printing of warnings to C<STDERR> to be suppressed. You can
-use this to save warnings in a variable, or turn warnings into fatal
-errors, like this:
-
- local $SIG{__WARN__} = sub { die $_[0] };
- eval $proggie;
-
-As the C<'IGNORE'> hook is not supported by C<__WARN__>, you can
-disable warnings using the empty subroutine:
-
- local $SIG{__WARN__} = sub {};
-
-The routine indicated by C<$SIG{__DIE__}> is called when a fatal
-exception is about to be thrown. The error message is passed as the
-first argument. When a C<__DIE__> hook routine returns, the exception
-processing continues as it would have in the absence of the hook,
-unless the hook routine itself exits via a C<goto &sub>, a loop exit,
-or a C<die()>. The C<__DIE__> handler is explicitly disabled during
-the call, so that you can die from a C<__DIE__> handler. Similarly
-for C<__WARN__>.
-
-Due to an implementation glitch, the C<$SIG{__DIE__}> hook is called
-even inside an C<eval()>. Do not use this to rewrite a pending
-exception in C<$@>, or as a bizarre substitute for overriding
-C<CORE::GLOBAL::die()>. This strange action at a distance may be fixed
-in a future release so that C<$SIG{__DIE__}> is only called if your
-program is about to exit, as was the original intent. Any other use is
-deprecated.
-
-C<__DIE__>/C<__WARN__> handlers are very special in one respect: they
-may be called to report (probable) errors found by the parser. In such
-a case the parser may be in inconsistent state, so any attempt to
-evaluate Perl code from such a handler will probably result in a
-segfault. This means that warnings or errors that result from parsing
-Perl should be used with extreme caution, like this:
-
- require Carp if defined $^S;
- Carp::confess("Something wrong") if defined &Carp::confess;
- die "Something wrong, but could not load Carp to give "
- . "backtrace...\n\t"
- . "To see backtrace try starting Perl with -MCarp switch";
-
-Here the first line will load C<Carp> I<unless> it is the parser who
-called the handler. The second line will print backtrace and die if
-C<Carp> was available. The third line will be executed only if C<Carp> was
-not available.
-
-Having to even think about the C<$^S> variable in your exception
-handlers is simply wrong. C<$SIG{__DIE__}> as currently implemented
-invites grievous and difficult to track down errors. Avoid it
-and use an C<END{}> or CORE::GLOBAL::die override instead.
-
-See L<perlfunc/die>, L<perlfunc/warn>, L<perlfunc/eval>, and
-L<warnings> for additional information.
-
-=item $BASETIME
-
-=item $^T
-X<$^T> X<$BASETIME>
-
-The time at which the program began running, in seconds since the
-epoch (beginning of 1970). The values returned by the B<-M>, B<-A>,
-and B<-C> filetests are based on this value.
-
-=item $PERL_VERSION
-
-=item $^V
-X<$^V> X<$PERL_VERSION>
-
-The revision, version, and subversion of the Perl interpreter,
-represented as a C<version> object.
-
-This variable first appeared in perl 5.6.0; earlier versions of perl
-will see an undefined value. Before perl 5.10.0 C<$^V> was represented
-as a v-string.
-
-C<$^V> can be used to determine whether the Perl interpreter executing
-a script is in the right range of versions. For example:
-
- warn "Hashes not randomized!\n" if !$^V or $^V lt v5.8.1
-
-To convert C<$^V> into its string representation use C<sprintf()>'s
-C<"%vd"> conversion:
-
- printf "version is v%vd\n", $^V; # Perl's version
-
-See the documentation of C<use VERSION> and C<require VERSION>
-for a convenient way to fail if the running Perl interpreter is too old.
-
-See also C<$]> for an older representation of the Perl version.
-
-This variable was added in Perl 5.6.
-
-Mnemonic: use ^V for Version Control.
-
-=item ${^WIN32_SLOPPY_STAT}
-X<${^WIN32_SLOPPY_STAT}> X<sitecustomize> X<sitecustomize.pl>
-
-If this variable is set to a true value, then C<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 variable could be set in the F<sitecustomize.pl> file to
-configure the local Perl installation to use "sloppy" C<stat()> by
-default. See the documentation for B<-f> in
-L<perlrun|perlrun/"Command Switches"> for more information about site
-customization.
-
-This variable was added in Perl 5.10.
-
-=item $EXECUTABLE_NAME
-
-=item $^X
-X<$^X> X<$EXECUTABLE_NAME>
-
-The name used to execute the current copy of Perl, from C's
-C<argv[0]> or (where supported) F</proc/self/exe>.
-
-Depending on the host operating system, the value of C<$^X> may be
-a relative or absolute pathname of the perl program file, or may
-be the string used to invoke perl but not the pathname of the
-perl program file. Also, most operating systems permit invoking
-programs that are not in the PATH environment variable, so there
-is no guarantee that the value of C<$^X> is in PATH. For VMS, the
-value may or may not include a version number.
-
-You usually can use the value of C<$^X> to re-invoke an independent
-copy of the same perl that is currently running, e.g.,
-
- @first_run = `$^X -le "print int rand 100 for 1..100"`;
-
-But recall that not all operating systems support forking or
-capturing of the output of commands, so this complex statement
-may not be portable.
-
-It is not safe to use the value of C<$^X> as a path name of a file,
-as some operating systems that have a mandatory suffix on
-executable files do not require use of the suffix when invoking
-a command. To convert the value of C<$^X> to a path name, use the
-following statements:
-
- # Build up a set of file names (not command names).
- use Config;
- my $this_perl = $^X;
- if ($^O ne 'VMS') {
- $this_perl .= $Config{_exe}
- unless $this_perl =~ m/$Config{_exe}$/i;
- }
-
-Because many operating systems permit anyone with read access to
-the Perl program file to make a copy of it, patch the copy, and
-then execute the copy, the security-conscious Perl programmer
-should take care to invoke the installed copy of perl, not the
-copy referenced by C<$^X>. The following statements accomplish
-this goal, and produce a pathname that can be invoked as a
-command or referenced as a file.
-
- use Config;
- my $secure_perl_path = $Config{perlpath};
- if ($^O ne 'VMS') {
- $secure_perl_path .= $Config{_exe}
- unless $secure_perl_path =~ m/$Config{_exe}$/i;
- }
-
-=back
-
-=head2 Variables related to regular expressions
-
-Most of the special variables related to regular expressions are side
-effects. Perl sets these variables when it has a successful match, so
-you should check the match result before using them. For instance:
-
- if( /P(A)TT(ER)N/ ) {
- print "I found $1 and $2\n";
- }
-
-These variables are read-only and dynamically-scoped, unless we note
-otherwise.
-
-The dynamic nature of the regular expression variables means that
-their value is limited to the block that they are in, as demonstrated
-by this bit of code:
-
- my $outer = 'Wallace and Grommit';
- my $inner = 'Mutt and Jeff';
-
- my $pattern = qr/(\S+) and (\S+)/;
-
- sub show_n { print "\$1 is $1; \$2 is $2\n" }
-
- {
- OUTER:
- show_n() if $outer =~ m/$pattern/;
-
- INNER: {
- show_n() if $inner =~ m/$pattern/;
- }
-
- show_n();
- }
-
-The output shows that while in the C<OUTER> block, the values of C<$1>
-and C<$2> are from the match against C<$outer>. Inside the C<INNER>
-block, the values of C<$1> and C<$2> are from the match against
-C<$inner>, but only until the end of the block (i.e. the dynamic
-scope). After the C<INNER> block completes, the values of C<$1> and
-C<$2> return to the values for the match against C<$outer> even though
-we have not made another match:
-
- $1 is Wallace; $2 is Grommit
- $1 is Mutt; $2 is Jeff
- $1 is Wallace; $2 is Grommit
-
-Due to an unfortunate accident of Perl's implementation, C<use
-English> imposes a considerable performance penalty on all regular
-expression matches in a program because it uses the C<$`>, C<$&>, and
-C<$'>, regardless of whether they occur in the scope of C<use
-English>. For that reason, saying C<use English> in libraries is
-strongly discouraged unless you import it without the match variables:
-
- use English '-no_match_vars'
-
-The C<Devel::NYTProf> and C<Devel::FindAmpersand>
-modules can help you find uses of these
-problematic match variables in your code.
-
-Since Perl 5.10, you can use the C</p> match operator flag and the
-C<${^PREMATCH}>, C<${^MATCH}>, and C<${^POSTMATCH}> variables instead
-so you only suffer the performance penalties.
-
-=over 8
-
-=item $<I<digits>> ($1, $2, ...)
-X<$1> X<$2> X<$3>
-
-Contains the subpattern from the corresponding set of capturing
-parentheses from the last successful pattern match, not counting patterns
-matched in nested blocks that have been exited already.
-
-These variables are read-only and dynamically-scoped.
-
-Mnemonic: like \digits.
-
-=item $MATCH
-
-=item $&
-X<$&> X<$MATCH>
-
-The string matched by the last successful pattern match (not counting
-any matches hidden within a BLOCK or C<eval()> enclosed by the current
-BLOCK).
-
-The use of this variable anywhere in a program imposes a considerable
-performance penalty on all regular expression matches. To avoid this
-penalty, you can extract the same substring by using L</@->. Starting
-with Perl 5.10, you can use the C</p> match flag and the C<${^MATCH}>
-variable to do the same thing for particular match operations.
-
-This variable is read-only and dynamically-scoped.
-
-Mnemonic: like C<&> in some editors.
-
-=item ${^MATCH}
-X<${^MATCH}>
-
-This is similar to C<$&> (C<$MATCH>) except that it does not incur the
-performance penalty associated with that variable, and is only guaranteed
-to return a defined value when the pattern was compiled or executed with
-the C</p> modifier.
-
-This variable was added in Perl 5.10.
-
-This variable is read-only and dynamically-scoped.
-
-=item $PREMATCH
-
-=item $`
-X<$`> X<$PREMATCH> X<${^PREMATCH}>
-
-The string preceding whatever was matched by the last successful
-pattern match, not counting any matches hidden within a BLOCK or C<eval>
-enclosed by the current BLOCK.
-
-The use of this variable anywhere in a program imposes a considerable
-performance penalty on all regular expression matches. To avoid this
-penalty, you can extract the same substring by using L</@->. Starting
-with Perl 5.10, you can use the C</p> match flag and the
-C<${^PREMATCH}> variable to do the same thing for particular match
-operations.
-
-This variable is read-only and dynamically-scoped.
-
-Mnemonic: C<`> often precedes a quoted string.
-
-=item ${^PREMATCH}
-X<$`> X<${^PREMATCH}>
-
-This is similar to C<$`> ($PREMATCH) except that it does not incur the
-performance penalty associated with that variable, and is only guaranteed
-to return a defined value when the pattern was compiled or executed with
-the C</p> modifier.
-
-This variable was added in Perl 5.10
-
-This variable is read-only and dynamically-scoped.
-
-=item $POSTMATCH
-
-=item $'
-X<$'> X<$POSTMATCH> X<${^POSTMATCH}> X<@->
-
-The string following whatever was matched by the last successful
-pattern match (not counting any matches hidden within a BLOCK or C<eval()>
-enclosed by the current BLOCK). Example:
-
- local $_ = 'abcdefghi';
- /def/;
- print "$`:$&:$'\n"; # prints abc:def:ghi
-
-The use of this variable anywhere in a program imposes a considerable
-performance penalty on all regular expression matches.
-To avoid this penalty, you can extract the same substring by
-using L</@->. Starting with Perl 5.10, you can use the C</p> match flag
-and the C<${^POSTMATCH}> variable to do the same thing for particular
-match operations.
-
-This variable is read-only and dynamically-scoped.
-
-Mnemonic: C<'> often follows a quoted string.
-
-=item ${^POSTMATCH}
-X<${^POSTMATCH}> X<$'> X<$POSTMATCH>
-
-This is similar to C<$'> (C<$POSTMATCH>) except that it does not incur the
-performance penalty associated with that variable, and is only guaranteed
-to return a defined value when the pattern was compiled or executed with
-the C</p> modifier.
-
-This variable was added in Perl 5.10.
-
-This variable is read-only and dynamically-scoped.
-
-=item $LAST_PAREN_MATCH
-
-=item $+
-X<$+> X<$LAST_PAREN_MATCH>
-
-The text matched by the last bracket of the last successful search pattern.
-This is useful if you don't know which one of a set of alternative patterns
-matched. For example:
-
- /Version: (.*)|Revision: (.*)/ && ($rev = $+);
-
-This variable is read-only and dynamically-scoped.
-
-Mnemonic: be positive and forward looking.
-
-=item $LAST_SUBMATCH_RESULT
-
-=item $^N
-X<$^N> X<$LAST_SUBMATCH_RESULT>
-
-The text matched by the used group most-recently closed (i.e. the group
-with the rightmost closing parenthesis) of the last successful search
-pattern.
-
-This is primarily used inside C<(?{...})> blocks for examining text
-recently matched. For example, to effectively capture text to a variable
-(in addition to C<$1>, C<$2>, etc.), replace C<(...)> with
-
- (?:(...)(?{ $var = $^N }))
-
-By setting and then using C<$var> in this way relieves you from having to
-worry about exactly which numbered set of parentheses they are.
-
-This variable was added in Perl 5.8.
-
-Mnemonic: the (possibly) Nested parenthesis that most recently closed.
-
-=item @LAST_MATCH_END
-
-=item @+
-X<@+> X<@LAST_MATCH_END>
-
-This array holds the offsets of the ends of the last successful
-submatches in the currently active dynamic scope. C<$+[0]> is
-the offset into the string of the end of the entire match. This
-is the same value as what the C<pos> function returns when called
-on the variable that was matched against. The I<n>th element
-of this array holds the offset of the I<n>th submatch, so
-C<$+[1]> is the offset past where C<$1> ends, C<$+[2]> the offset
-past where C<$2> ends, and so on. You can use C<$#+> to determine
-how many subgroups were in the last successful match. See the
-examples given for the C<@-> variable.
-
-This variable was added in Perl 5.6.
-
-=item %LAST_PAREN_MATCH
-
-=item %+
-X<%+> X<%LAST_PAREN_MATCH>
-
-Similar to C<@+>, the C<%+> hash allows access to the named capture
-buffers, should they exist, in the last successful match in the
-currently active dynamic scope.
-
-For example, C<$+{foo}> is equivalent to C<$1> after the following match:
-
- 'foo' =~ /(?<foo>foo)/;
-
-The keys of the C<%+> hash list only the names of buffers that have
-captured (and that are thus associated to defined values).
-
-The underlying behaviour of C<%+> is provided by the
-L<Tie::Hash::NamedCapture> module.
-
-B<Note:> C<%-> and C<%+> are tied views into a common internal hash
-associated with the last successful regular expression. Therefore mixing
-iterative access to them via C<each> may have unpredictable results.
-Likewise, if the last successful match changes, then the results may be
-surprising.
-
-This variable was added in Perl 5.10.
-
-This variable is read-only and dynamically-scoped.
-
-=item @LAST_MATCH_START
-
-=item @-
-X<@-> X<@LAST_MATCH_START>
-
-C<$-[0]> is the offset of the start of the last successful match.
-C<$-[>I<n>C<]> is the offset of the start of the substring matched by
-I<n>-th subpattern, or undef if the subpattern did not match.
-
-Thus, after a match against C<$_>, C<$&> coincides with C<substr $_, $-[0],
-$+[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<@+>.
-
-This array holds the offsets of the beginnings of the last
-successful submatches in the currently active dynamic scope.
-C<$-[0]> is the offset into the string of the beginning of the
-entire match. The I<n>th element of this array holds the offset
-of the I<n>th submatch, so C<$-[1]> is the offset where C<$1>
-begins, C<$-[2]> the offset where C<$2> begins, and so on.
-
-After a match against some variable C<$var>:
-
-=over 5
-
-=item C<$`> is the same as C<substr($var, 0, $-[0])>
-
-=item C<$&> is the same as C<substr($var, $-[0], $+[0] - $-[0])>
-
-=item C<$'> is the same as C<substr($var, $+[0])>
-
-=item C<$1> is the same as C<substr($var, $-[1], $+[1] - $-[1])>
-
-=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])>
-
-=back
-
-This variable was added in Perl 5.6.
-
-=item %LAST_MATCH_START
-
-=item %-
-X<%-> X<%LAST_MATCH_START>
-
-Similar to C<%+>, this variable allows access to the named capture groups
-in the last successful match in the currently active dynamic scope. To
-each capture group name found in the regular expression, it associates a
-reference to an array containing the list of values captured by all
-buffers with that name (should there be several of them), in the order
-where they appear.
-
-Here's an example:
-
- if ('1234' =~ /(?<A>1)(?<B>2)(?<A>3)(?<B>4)/) {
- foreach my $bufname (sort keys %-) {
- my $ary = $-{$bufname};
- foreach my $idx (0..$#$ary) {
- print "\$-{$bufname}[$idx] : ",
- (defined($ary->[$idx])
- ? "'$ary->[$idx]'"
- : "undef"),
- "\n";
- }
- }
- }
-
-would print out:
-
- $-{A}[0] : '1'
- $-{A}[1] : '3'
- $-{B}[0] : '2'
- $-{B}[1] : '4'
-
-The keys of the C<%-> hash correspond to all buffer names found in
-the regular expression.
-
-The behaviour of C<%-> is implemented via the
-L<Tie::Hash::NamedCapture> module.
-
-B<Note:> C<%-> and C<%+> are tied views into a common internal hash
-associated with the last successful regular expression. Therefore mixing
-iterative access to them via C<each> may have unpredictable results.
-Likewise, if the last successful match changes, then the results may be
-surprising.
-
-This variable was added in Perl 5.10
-
-This variable is read-only and dynamically-scoped.
-
-=item $LAST_REGEXP_CODE_RESULT
-
-=item $^R
-X<$^R> X<$LAST_REGEXP_CODE_RESULT>
-
-The result of evaluation of the last successful C<(?{ code })>
-regular expression assertion (see L<perlre>). May be written to.
-
-This variable was added in Perl 5.005.
-
-=item ${^RE_DEBUG_FLAGS}
-X<${^RE_DEBUG_FLAGS}>
-
-The current value of the regex debugging flags. Set to 0 for no debug output
-even when the C<re 'debug'> module is loaded. See L<re> for details.
-
-This variable was added in Perl 5.10.
-
-=item ${^RE_TRIE_MAXBUF}
-X<${^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.
-
-This variable was added in Perl 5.10.
-
-=back
-
-=head2 Variables related to filehandles
-
-Variables that depend on the currently selected filehandle may be set
-by calling an appropriate object method on the C<IO::Handle> object,
-although this is less efficient than using the regular built-in
-variables. (Summary lines below for this contain the word HANDLE.)
-First you must say
-
- use IO::Handle;
-
-after which you may use either
-
- method HANDLE EXPR
-
-or more safely,
-
- HANDLE->method(EXPR)
-
-Each method returns the old value of the C<IO::Handle> attribute. The
-methods each take an optional EXPR, which, if supplied, specifies the
-new value for the C<IO::Handle> attribute in question. If not
-supplied, most methods do nothing to the current value--except for
-C<autoflush()>, which will assume a 1 for you, just to be different.
-
-Because loading in the C<IO::Handle> class is an expensive operation,
-you should learn how to use the regular built-in variables.
-
-A few of these variables are considered "read-only". This means that
-if you try to assign to this variable, either directly or indirectly
-through a reference, you'll raise a run-time exception.
-
-You should be very careful when modifying the default values of most
-special variables described in this document. In most cases you want
-to localize these variables before changing them, since if you don't,
-the change may affect other modules which rely on the default values
-of the special variables that you have changed. This is one of the
-correct ways to read the whole file at once:
-
- open my $fh, "<", "foo" or die $!;
- local $/; # enable localized slurp mode
- my $content = <$fh>;
- close $fh;
-
-But the following code is quite bad:
-
- open my $fh, "<", "foo" or die $!;
- undef $/; # enable slurp mode
- my $content = <$fh>;
- close $fh;
-
-since some other module, may want to read data from some file in the
-default "line mode", so if the code we have just presented has been
-executed, the global value of C<$/> is now changed for any other code
-running inside the same Perl interpreter.
-
-Usually when a variable is localized you want to make sure that this
-change affects the shortest scope possible. So unless you are already
-inside some short C<{}> block, you should create one yourself. For
-example:
-
- my $content = '';
- open my $fh, "<", "foo" or die $!;
- {
- local $/;
- $content = <$fh>;
- }
- close $fh;
-
-Here is an example of how your own code can go broken:
-
- for ( 1..3 ){
- $\ = "\r\n";
- nasty_break();
- print "$_";
- }
-
- sub nasty_break {
- $\ = "\f";
- # do something with $_
- }
-
-You probably expect this code to print the equivalent of
-
- "1\r\n2\r\n3\r\n"
-
-but instead you get:
-
- "1\f2\f3\f"
-
-Why? Because C<nasty_break()> modifies C<$\> without localizing it
-first. The value you set in C<nasty_break()> is still there when you
-return. The fix is to add C<local()> so the value doesn't leak out of
-C<nasty_break()>:
-
- local $\ = "\f";
-
-It's easy to notice the problem in such a short example, but in more
-complicated code you are looking for trouble if you don't localize
-changes to the special variables.
-
-=over 8
-
-=item $ARGV
-X<$ARGV>
-
-Contains the name of the current file when reading from C<< <> >>.
-
-=item @ARGV
-X<@ARGV>
-
-The array C<@ARGV> contains the command-line arguments intended for
-the script. C<$#ARGV> is generally the number of arguments minus
-one, because C<$ARGV[0]> is the first argument, I<not> the program's
-command name itself. See L</$0> for the command name.
-
-=item ARGV
-X<ARGV>
-
-The special filehandle that iterates over command-line filenames in
-C<@ARGV>. Usually written as the null filehandle in the angle operator
-C<< <> >>. Note that currently C<ARGV> only has its magical effect
-within the C<< <> >> operator; elsewhere it is just a plain filehandle
-corresponding to the last file opened by C<< <> >>. In particular,
-passing C<\*ARGV> as a parameter to a function that expects a filehandle
-may not cause your function to automatically read the contents of all the
-files in C<@ARGV>.
-
-=item ARGVOUT
-X<ARGVOUT>
-
-The special filehandle that points to the currently open output file
-when doing edit-in-place processing with B<-i>. Useful when you have
-to do a lot of inserting and don't want to keep modifying C<$_>. See
-L<perlrun> for the B<-i> switch.
-
-=item Handle->output_field_separator( EXPR )
-
-=item $OUTPUT_FIELD_SEPARATOR
-
-=item $OFS
-
-=item $,
-X<$,> X<$OFS> X<$OUTPUT_FIELD_SEPARATOR>
-
-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 HANDLE->input_line_number( EXPR )
-
-=item $INPUT_LINE_NUMBER
-
-=item $NR
-
-=item $.
-X<$.> X<$NR> X<$INPUT_LINE_NUMBER> X<line number>
-
-Current line number for the last filehandle accessed.
-
-Each filehandle in Perl counts the number of lines that have been read
-from it. (Depending on the value of C<$/>, Perl's idea of what
-constitutes a line may not match yours.) When a line is read from a
-filehandle (via C<readline()> or C<< <> >>), or when C<tell()> or
-C<seek()> is called on it, C<$.> becomes an alias to the line counter
-for that filehandle.
-
-You can adjust the counter by assigning to C<$.>, but this will not
-actually move the seek pointer. I<Localizing C<$.> will not localize
-the filehandle's line count>. Instead, it will localize perl's notion
-of which filehandle C<$.> is currently aliased to.
-
-C<$.> is reset when the filehandle is closed, but B<not> when an open
-filehandle is reopened without an intervening C<close()>. For more
-details, see L<perlop/"IE<sol>O Operators">. Because C<< <> >> never does
-an explicit close, line numbers increase across C<ARGV> files (but see
-examples in L<perlfunc/eof>).
-
-You can also use C<< HANDLE->input_line_number(EXPR) >> to access the
-line counter for a given filehandle without having to worry about
-which handle you last accessed.
-
-Mnemonic: many programs use "." to mean the current line number.
-
-=item HANDLE->input_record_separator( EXPR )
-
-=item $INPUT_RECORD_SEPARATOR
-
-=item $RS
-
-=item $/
-X<$/> X<$RS> X<$INPUT_RECORD_SEPARATOR>
-
-The input record separator, newline by default. This influences Perl's
-idea of what a "line" is. Works like B<awk>'s RS variable, including
-treating empty lines as a terminator if set to the null string (an
-empty line cannot contain any spaces or tabs). You may set it to a
-multi-character string to match a multi-character terminator, or to
-C<undef> to read through the end of file. Setting it to C<"\n\n">
-means something slightly different than setting to C<"">, if the file
-contains consecutive empty lines. Setting to C<""> will treat two or
-more consecutive empty lines as a single empty line. Setting to
-C<"\n\n"> will blindly assume that the next input character belongs to
-the next paragraph, even if it's a newline.
-
- local $/; # enable "slurp" mode
- local $_ = <FH>; # whole file now here
- s/\n[ \t]+/ /g;
-
-Remember: the value of C<$/> is a string, not a regex. B<awk> has to
-be better for something. :-)
-
-Setting C<$/> to a reference to an integer, scalar containing an
-integer, or scalar that's convertible to an integer will attempt to
-read records instead of lines, with the maximum record size being the
-referenced integer. So this:
-
- local $/ = \32768; # or \"32768", or \$var_containing_32768
- open my $fh, "<", $myfile or die $!;
- local $_ = <$fh>;
-
-will read a record of no more than 32768 bytes from FILE. If you're
-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. Trying to set the record
-size to zero or less will cause reading in the (rest of the) whole file.
-
-On VMS only, record reads bypass PerlIO layers and any associated
-buffering,so you must not mix record and non-record reads on the
-same filehandle. Record mode mixes with line mode only when the
-same buffering layer is in use for both modes.
-
-If you perform a record read on a FILE with an encoding layer such as
-C<:encoding(latin1)> or C<:utf8>, you may get an invalid string as a
-result, may leave the FILE positioned between characters in the stream
-and may not be reading the number of bytes from the underlying file
-that you specified. This behaviour may change without warning in a
-future version of perl.
-
-See also L<perlport/"Newlines">. Also see L</$.>.
-
-Mnemonic: / delimits line boundaries when quoting poetry.
-
-=item Handle->output_record_separator( EXPR )
-
-=item $OUTPUT_RECORD_SEPARATOR
-
-=item $ORS
-
-=item $\
-X<$\> X<$ORS> X<$OUTPUT_RECORD_SEPARATOR>
-
-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 HANDLE->autoflush( EXPR )
-
-=item $OUTPUT_AUTOFLUSH
-
-=item $|
-X<$|> X<autoflush> X<flush> X<$OUTPUT_AUTOFLUSH>
-
-If set to nonzero, forces a flush right away and after every write or
-print on the currently selected output channel. Default is 0
-(regardless of whether the channel is really buffered by the system or
-not; C<$|> tells you only whether you've asked Perl explicitly to
-flush after each write). STDOUT will typically be line buffered if
-output is to the terminal and block buffered otherwise. Setting this
-variable is useful primarily when you are outputting to a pipe or
-socket, such as when you are running a Perl program under B<rsh> and
-want to see the output as it's happening. This has no effect on input
-buffering. See L<perlfunc/getc> for that. See L<perlfunc/select> on
-how to select the output channel. See also L<IO::Handle>.
-
-Mnemonic: when you want your pipes to be piping hot.
-
-=back
-
-=head3 Variables related to formats
-
-The special variables for formats are a subset of those for
-filehandles. See L<perlform> for more information about Perl's
-formats.
-
-=over 8
-
-=item $ACCUMULATOR
-
-=item $^A
-X<$^A> X<$ACCUMULATOR>
-
-The current value of the C<write()> accumulator for C<format()> lines.
-A format contains C<formline()> calls that put their result into
-C<$^A>. After calling its format, C<write()> prints out the contents
-of C<$^A> and empties. So you never really see the contents of C<$^A>
-unless you call C<formline()> yourself and then look at it. See
-L<perlform> and L<perlfunc/"formline PICTURE,LIST">.
-
-=item HANDLE->format_formfeed(EXPR)
-
-=item $FORMAT_FORMFEED
-
-=item $^L
-X<$^L> X<$FORMAT_FORMFEED>
-
-What formats output as a form feed. The default is C<\f>.
-
-=item HANDLE->format_page_number(EXPR)
-
-=item $FORMAT_PAGE_NUMBER
-
-=item $%
-X<$%> X<$FORMAT_PAGE_NUMBER>
-
-The current page number of the currently selected output channel.
-
-Mnemonic: C<%> is page number in B<nroff>.
-
-=item HANDLE->format_lines_left(EXPR)
-
-=item $FORMAT_LINES_LEFT
-
-=item $-
-X<$-> X<$FORMAT_LINES_LEFT>
-
-The number of lines left on the page of the currently selected output
-channel.
-
-Mnemonic: lines_on_page - lines_printed.
-
-=item Handle->format_line_break_characters EXPR
-
-=item $FORMAT_LINE_BREAK_CHARACTERS
-
-=item $:
-X<$:> X<FORMAT_LINE_BREAK_CHARACTERS>
-
-The current set of characters after which a string may be broken to
-fill continuation fields (starting with C<^>) in a format. The default is
-S<" \n-">, to break on a space, newline, or a hyphen.
-
-Mnemonic: a "colon" in poetry is a part of a line.
-
-=item HANDLE->format_lines_per_page(EXPR)
-
-=item $FORMAT_LINES_PER_PAGE
-
-=item $=
-X<$=> X<$FORMAT_LINES_PER_PAGE>
-
-The current page length (printable lines) of the currently selected
-output channel. The default is 60.
-
-Mnemonic: = has horizontal lines.
-
-=item HANDLE->format_top_name(EXPR)
-
-=item $FORMAT_TOP_NAME
-
-=item $^
-X<$^> X<$FORMAT_TOP_NAME>
-
-The name of the current top-of-page format for the currently selected
-output channel. The default is the name of the filehandle with C<_TOP>
-appended. For example, the default format top name for the C<STDOUT>
-filehandle is C<STDOUT_TOP>.
-
-Mnemonic: points to top of page.
-
-=item HANDLE->format_name(EXPR)
-
-=item $FORMAT_NAME
-
-=item $~
-X<$~> X<$FORMAT_NAME>
-
-The name of the current report format for the currently selected
-output channel. The default format name is the same as the filehandle
-name. For example, the default format name for the C<STDOUT>
-filehandle is just C<STDOUT>.
-
-Mnemonic: brother to C<$^>.
-
-=back
-
-=head2 Error Variables
-X<error> X<exception>
-
-The variables C<$@>, C<$!>, C<$^E>, and C<$?> contain information
-about different types of error conditions that may appear during
-execution of a Perl program. The variables are shown ordered by
-the "distance" between the subsystem which reported the error and
-the Perl process. They correspond to errors detected by the Perl
-interpreter, C library, operating system, or an external program,
-respectively.
-
-To illustrate the differences between these variables, consider the
-following Perl expression, which uses a single-quoted string. After
-execution of this statement, perl may have set all four special error
-variables:
-
- eval q{
- open my $pipe, "/cdrom/install |" or die $!;
- my @res = <$pipe>;
- close $pipe or die "bad pipe: $?, $!";
- };
-
-When perl executes the C<eval()> expression, it translates the
-C<open()>, C<< <PIPE> >>, and C<close> calls in the C run-time library
-and thence to the operating system kernel. perl sets C<$!> to
-the C library's C<errno> if one of these calls fails.
-
-C<$@> is set if the string to be C<eval>-ed did not compile (this may
-happen if C<open> or C<close> were imported with bad prototypes), or
-if Perl code executed during evaluation C<die()>d. In these cases the
-value of C<$@> is the compile error, or the argument to C<die> (which
-will interpolate C<$!> and C<$?>). (See also L<Fatal>, though.)
-
-Under a few operating systems, C<$^E> may contain a more verbose error
-indicator, such as in this case, "CDROM tray not closed." Systems that
-do not support extended error messages leave C<$^E> the same as C<$!>.
-
-Finally, C<$?> may be set to non-0 value if the external program
-F</cdrom/install> fails. The upper eight bits reflect specific error
-conditions encountered by the program (the program's C<exit()> value).
-The lower eight bits reflect mode of failure, like signal death and
-core dump information. See L<wait(2)> for details. In contrast to
-C<$!> and C<$^E>, which are set only if error condition is detected,
-the variable C<$?> is set on each C<wait> or pipe C<close>,
-overwriting the old value. This is more like C<$@>, which on every
-C<eval()> is always set on failure and cleared on success.
-
-For more details, see the individual descriptions at C<$@>, C<$!>,
-C<$^E>, and C<$?>.
-
-=over 8
-
-=item ${^CHILD_ERROR_NATIVE}
-X<$^CHILD_ERROR_NATIVE>
-
-The native status returned by the last pipe close, backtick (C<``>)
-command, successful call to C<wait()> or C<waitpid()>, or from the
-C<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 C<$?> when the pragma C<use vmsish 'status'> is in effect.
-
-This variable was added in Perl 5.8.9.
-
-=item $EXTENDED_OS_ERROR
-
-=item $^E
-X<$^E> X<$EXTENDED_OS_ERROR>
-
-Error information specific to the current operating system. At the
-moment, this differs from C<$!> under only VMS, OS/2, and Win32 (and
-for MacPerl). On all other platforms, C<$^E> is always just the same
-as C<$!>.
-
-Under VMS, C<$^E> provides the VMS status value from the last system
-error. This is more specific information about the last system error
-than that provided by C<$!>. This is particularly important when C<$!>
-is set to B<EVMSERR>.
-
-Under OS/2, C<$^E> is set to the error code of the last call to OS/2
-API either via CRT, or directly from perl.
-
-Under Win32, C<$^E> always returns the last error information reported
-by the Win32 call C<GetLastError()> which describes the last error
-from within the Win32 API. Most Win32-specific code will report errors
-via C<$^E>. ANSI C and Unix-like calls set C<errno> and so most
-portable Perl code will report errors via C<$!>.
-
-Caveats mentioned in the description of C<$!> generally apply to
-C<$^E>, also.
-
-This variable was added in Perl 5.003.
-
-Mnemonic: Extra error explanation.
-
-=item $EXCEPTIONS_BEING_CAUGHT
-
-=item $^S
-X<$^S> X<$EXCEPTIONS_BEING_CAUGHT>
-
-Current state of the interpreter.
-
- $^S State
- --------- -------------------
- undef Parsing module/eval
- true (1) Executing an eval
- false (0) Otherwise
-
-The first state may happen in C<$SIG{__DIE__}> and C<$SIG{__WARN__}>
-handlers.
-
-This variable was added in Perl 5.004.
-
-=item $WARNING
-
-=item $^W
-X<$^W> X<$WARNING>
-
-The current value of the warning switch, initially true if B<-w> was
-used, false otherwise, but directly modifiable.
-
-See also L<warnings>.
-
-Mnemonic: related to the B<-w> switch.
-
-=item ${^WARNING_BITS}
-X<${^WARNING_BITS}>
-
-The current set of warning checks enabled by the C<use warnings> pragma.
-It has the same scoping as the C<$^H> and C<%^H> variables. The exact
-values are considered internal to the L<warnings> pragma and may change
-between versions of Perl.
-
-This variable was added in Perl 5.6.
-
-=item $OS_ERROR
-
-=item $ERRNO
-
-=item $!
-X<$!> X<$ERRNO> X<$OS_ERROR>
-
-When referenced, C<$!> retrieves the current value
-of the C C<errno> integer variable.
-If C<$!> is assigned a numerical value, that value is stored in C<errno>.
-When referenced as a string, C<$!> yields the system error string
-corresponding to C<errno>.
-
-Many system or library calls set C<errno> if they fail,
-to indicate the cause of failure. They usually do B<not>
-set C<errno> to zero if they succeed. This means C<errno>,
-hence C<$!>, is meaningful only I<immediately> after a B<failure>:
-
- if (open my $fh, "<", $filename) {
- # Here $! is meaningless.
- ...
- }
- else {
- # ONLY here is $! meaningful.
- ...
- # Already here $! might be meaningless.
- }
- # Since here we might have either success or failure,
- # $! is meaningless.
-
-Here, I<meaningless> means that C<$!> may be unrelated to the outcome
-of the C<open()> operator. Assignment to C<$!> is similarly ephemeral.
-It can be used immediately before invoking the C<die()> operator,
-to set the exit value, or to inspect the system error string
-corresponding to error I<n>, or to restore C<$!> to a meaningful state.
-
-Mnemonic: What just went bang?
-
-=item %OS_ERROR
-
-=item %ERRNO
-
-=item %!
-X<%!> X<%OS_ERROR> X<%ERRNO>
-
-Each element of C<%!> has a true value only if C<$!> is set to that
-value. For example, C<$!{ENOENT}> is true if and only if the current
-value of C<$!> is C<ENOENT>; that is, if the most recent error was "No
-such file or directory" (or its moral equivalent: not all operating
-systems give that exact error, and certainly not all languages). To
-check if a particular key is meaningful on your system, use C<exists
-$!{the_key}>; for a list of legal keys, use C<keys %!>. See L<Errno>
-for more information, and also see L</$!>.
-
-This variable was added in Perl 5.005.
-
-=item $CHILD_ERROR
-
-=item $?
-X<$?> X<$CHILD_ERROR>
-
-The status returned by the last pipe close, backtick (C<``>) command,
-successful call to C<wait()> or C<waitpid()>, or from the C<system()>
-operator. This is just the 16-bit status word returned by the
-traditional Unix C<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<$? & 128> reports whether there was a core dump.
-
-Additionally, if the C<h_errno> variable is supported in C, its value
-is returned via C<$?> if any C<gethost*()> function fails.
-
-If you have installed a signal handler for C<SIGCHLD>, the
-value of C<$?> will usually be wrong outside that handler.
-
-Inside an C<END> subroutine C<$?> contains the value that is going to be
-given to C<exit()>. You can modify C<$?> in an C<END> subroutine to
-change the exit status of your program. For example:
-
- END {
- $? = 1 if $? == 255; # die would make it 255
- }
-
-Under VMS, the pragma C<use vmsish 'status'> makes C<$?> reflect the
-actual VMS exit status, instead of the default emulation of POSIX
-status; see L<perlvms/$?> for details.
-
-Mnemonic: similar to B<sh> and B<ksh>.
-
-=item $EVAL_ERROR
-
-=item $@
-X<$@> X<$EVAL_ERROR>
-
-The Perl syntax error message from the
-last C<eval()> operator. If C<$@> is
-the null string, the last C<eval()> parsed and executed correctly
-(although the operations you invoked may have failed in the normal
-fashion).
-
-Warning messages are not collected in this variable. You can, however,
-set up a routine to process warnings by setting C<$SIG{__WARN__}> as
-described in L</%SIG>.
-
-Mnemonic: Where was the syntax error "at"?
-
-=back
-
-=head2 Variables related to the interpreter state
-
-These variables provide information about the current interpreter state.
-
-=over 8
-
-=item $COMPILING
-
-=item $^C
-X<$^C> X<$COMPILING>
-
-The current value of the flag associated with the B<-c> switch.
-Mainly of use with B<-MO=...> to allow code to alter its behavior
-when being compiled, such as for example to C<AUTOLOAD> at compile
-time rather than normal, deferred loading. Setting
-C<$^C = 1> is similar to calling C<B::minus_c>.
-
-This variable was added in Perl 5.6.
-
-=item $DEBUGGING
-
-=item $^D
-X<$^D> X<$DEBUGGING>
-
-The current value of the debugging flags. May be read or set. Like its
-command-line equivalent, you can use numeric or symbolic values, eg
-C<$^D = 10> or C<$^D = "st">.
-
-Mnemonic: value of B<-D> switch.
-
-=item ${^ENCODING}
-X<${^ENCODING}>
-
-The I<object reference> to the C<Encode> object that is used to convert
-the source code to Unicode. Thanks to this variable your Perl script
-does not have to be written in UTF-8. Default is I<undef>. The direct
-manipulation of this variable is highly discouraged.
-
-This variable was added in Perl 5.8.2.
-
-=item ${^GLOBAL_PHASE}
-X<${^GLOBAL_PHASE}>
-
-The current phase of the perl interpreter.
-
-Possible values are:
-
-=over 8
-
-=item CONSTRUCT
-
-The C<PerlInterpreter*> is being constructed via C<perl_construct>. This
-value is mostly there for completeness and for use via the
-underlying C variable C<PL_phase>. It's not really possible for Perl
-code to be executed unless construction of the interpreter is
-finished.
-
-=item START
-
-This is the global compile-time. That includes, basically, every
-C<BEGIN> block executed directly or indirectly from during the
-compile-time of the top-level program.
-
-This phase is not called "BEGIN" to avoid confusion with
-C<BEGIN>-blocks, as those are executed during compile-time of any
-compilation unit, not just the top-level program. A new, localised
-compile-time entered at run-time, for example by constructs as
-C<eval "use SomeModule"> are not global interpreter phases, and
-therefore aren't reflected by C<${^GLOBAL_PHASE}>.
-
-=item CHECK
-
-Execution of any C<CHECK> blocks.
-
-=item INIT
-
-Similar to "CHECK", but for C<INIT>-blocks, not C<CHECK> blocks.
-
-=item RUN
-
-The main run-time, i.e. the execution of C<PL_main_root>.
-
-=item END
-
-Execution of any C<END> blocks.
-
-=item DESTRUCT
-
-Global destruction.
-
-=back
-
-Also note that there's no value for UNITCHECK-blocks. That's because
-those are run for each compilation unit individually, and therefore is
-not a global interpreter phase.
-
-Not every program has to go through each of the possible phases, but
-transition from one phase to another can only happen in the order
-described in the above list.
-
-An example of all of the phases Perl code can see:
-
- BEGIN { print "compile-time: ${^GLOBAL_PHASE}\n" }
-
- INIT { print "init-time: ${^GLOBAL_PHASE}\n" }
-
- CHECK { print "check-time: ${^GLOBAL_PHASE}\n" }
-
- {
- package Print::Phase;
-
- sub new {
- my ($class, $time) = @_;
- return bless \$time, $class;
- }
-
- sub DESTROY {
- my $self = shift;
- print "$$self: ${^GLOBAL_PHASE}\n";
- }
- }
-
- print "run-time: ${^GLOBAL_PHASE}\n";
-
- my $runtime = Print::Phase->new(
- "lexical variables are garbage collected before END"
- );
-
- END { print "end-time: ${^GLOBAL_PHASE}\n" }
-
- our $destruct = Print::Phase->new(
- "package variables are garbage collected after END"
- );
-
-This will print out
-
- compile-time: START
- check-time: CHECK
- init-time: INIT
- run-time: RUN
- lexical variables are garbage collected before END: RUN
- end-time: END
- package variables are garbage collected after END: DESTRUCT
-
-This variable was added in Perl 5.14.0.
-
-=item $^H
-X<$^H>
-
-WARNING: This variable is strictly for
-internal use only. Its availability,
-behavior, and contents are subject to change without notice.
-
-This variable contains compile-time hints for the Perl interpreter. At the
-end of compilation of a BLOCK the value of this variable is restored to the
-value when the interpreter started to compile the BLOCK.
-
-When perl begins to parse any block construct that provides a lexical scope
-(e.g., eval body, required file, subroutine body, loop body, or conditional
-block), the existing value of C<$^H> is saved, but its value is left unchanged.
-When the compilation of the block is completed, it regains the saved value.
-Between the points where its value is saved and restored, code that
-executes within BEGIN blocks is free to change the value of C<$^H>.
-
-This behavior provides the semantic of lexical scoping, and is used in,
-for instance, the C<use strict> pragma.
-
-The contents should be an integer; different bits of it are used for
-different pragmatic flags. Here's an example:
-
- sub add_100 { $^H |= 0x100 }
-
- sub foo {
- BEGIN { add_100() }
- bar->baz($boon);
- }
-
-Consider what happens during execution of the BEGIN block. At this point
-the BEGIN block has already been compiled, but the body of C<foo()> is still
-being compiled. The new value of C<$^H>
-will therefore be visible only while
-the body of C<foo()> is being compiled.
-
-Substitution of C<BEGIN { add_100() }> block with:
-
- BEGIN { require strict; strict->import('vars') }
-
-demonstrates how C<use strict 'vars'> is implemented. Here's a conditional
-version of the same lexical pragma:
-
- BEGIN {
- require strict; strict->import('vars') if $condition
- }
-
-This variable was added in Perl 5.003.
-
-=item %^H
-X<%^H>
-
-The C<%^H> hash provides the same scoping semantic as C<$^H>. This makes
-it useful for implementation of lexically scoped pragmas. See
-L<perlpragma>.
-
-When putting items into C<%^H>, in order to avoid conflicting with other
-users of the hash there is a convention regarding which keys to use.
-A module should use only keys that begin with the module's name (the
-name of its main package) and a "/" character. For example, a module
-C<Foo::Bar> should use keys such as C<Foo::Bar/baz>.
-
-This variable was added in Perl 5.6.
-
-=item ${^OPEN}
-X<${^OPEN}>
-
-An internal variable used by PerlIO. A string in two parts, separated
-by a C<\0> byte, the first part describes the input layers, the second
-part describes the output layers.
-
-This variable was added in Perl 5.8.0.
-
-=item $PERLDB
-
-=item $^P
-X<$^P> X<$PERLDB>
-
-The internal variable for debugging support. The meanings of the
-various bits are subject to change, but currently indicate:
-
-=over 6
-
-=item 0x01
-
-Debug subroutine enter/exit.
-
-=item 0x02
-
-Line-by-line debugging. Causes C<DB::DB()> subroutine to be called for
-each statement executed. Also causes saving source code lines (like
-0x400).
-
-=item 0x04
-
-Switch off optimizations.
-
-=item 0x08
-
-Preserve more data for future interactive inspections.
-
-=item 0x10
-
-Keep info about source lines on which a subroutine is defined.
-
-=item 0x20
-
-Start with single-step on.
-
-=item 0x40
-
-Use subroutine address instead of name when reporting.
-
-=item 0x80
-
-Report C<goto &subroutine> as well.
-
-=item 0x100
-
-Provide informative "file" names for evals based on the place they were compiled.
-
-=item 0x200
-
-Provide informative names to anonymous subroutines based on the place they
-were compiled.
-
-=item 0x400
-
-Save source code lines into C<@{"_<$filename"}>.
-
-=back
-
-Some bits may be relevant at compile-time only, some at
-run-time only. This is a new mechanism and the details may change.
-See also L<perldebguts>.
-
-=item ${^TAINT}
-X<${^TAINT}>
-
-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.
-
-This variable was added in Perl 5.8.
-
-=item ${^UNICODE}
-X<${^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.
-
-This variable was added in Perl 5.8.2.
-
-=item ${^UTF8CACHE}
-X<${^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.
-
-This variable was added in Perl 5.8.9.
-
-=item ${^UTF8LOCALE}
-X<${^UTF8LOCALE}>
-
-This variable indicates whether a 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.
-
-This variable was added in Perl 5.8.8.
-
-=back
-
-=head2 Deprecated and removed variables
-
-Deprecating a variable announces the intent of the perl maintainers to
-eventually remove the variable from the language. It may still be
-available despite its status. Using a deprecated variable triggers
-a warning.
-
-Once a variable is removed, its use triggers an error telling you
-the variable is unsupported.
-
-See L<perldiag> for details about error messages.
-
-=over 8
-
-=item $OFMT
-
-=item $#
-X<$#> X<$OFMT>
-
-C<$#> was a variable that could be used to format printed numbers.
-After a deprecation cycle, its magic was removed in Perl 5.10 and
-using it now triggers a warning: C<$# is no longer supported>.
-
-This is not the sigil you use in front of an array name to get the
-last index, like C<$#array>. That's still how you get the last index
-of an array in Perl. The two have nothing to do with each other.
-
-Deprecated in Perl 5.
-
-Removed in Perl 5.10.
-
-=item $*
-X<$*>
-
-C<$*> was a variable that you could use to enable multiline matching.
-After a deprecation cycle, its magic was removed in Perl 5.10.
-Using it now triggers a warning: C<$* is no longer supported>.
-You should use the C</s> and C</m> regexp modifiers instead.
-
-Deprecated in Perl 5.
-
-Removed in Perl 5.10.
-
-=item $ARRAY_BASE
-
-=item $[
-X<$[> X<$ARRAY_BASE>
-
-This variable stores the index of the first element in an array, and
-of the first character in a substring. The default is 0, but you could
-theoretically set it to 1 to make Perl behave more like B<awk> (or Fortran)
-when subscripting and when evaluating the index() and substr() functions.
-
-As of release 5 of Perl, assignment to C<$[> 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.
-
-Prior to Perl 5.10, assignment to C<$[> could be seen from outer lexical
-scopes in the same file, unlike other compile-time directives (such as
-L<strict>). Using local() on it would bind its value strictly to a lexical
-block. Now it is always lexically scoped.
-
-As of Perl 5.16, it is implemented by the L<arybase> module. See
-L<arybase> for more details on its behaviour.
-
-Under C<use v5.16>, or C<no feature "array_base">, C<$[> no longer has any
-effect, and always contains 0. Assigning 0 to it is permitted, but any
-other value will produce an error.
-
-Mnemonic: [ begins subscripts.
-
-Deprecated in Perl 5.12.
-
-=item $OLD_PERL_VERSION
-
-=item $]
-X<$]> X<$OLD_PERL_VERSION>
-
-See L</$^V> for a more modern representation of the Perl version that allows
-accurate string comparisons.
-
-The version + patchlevel / 1000 of the Perl interpreter. This variable
-can be used to determine whether the Perl interpreter executing a
-script is in the right range of versions:
-
- warn "No checksumming!\n" if $] < 3.019;
-
-The floating point representation can sometimes lead to inaccurate
-numeric comparisons.
-
-See also the documentation of C<use VERSION> and C<require VERSION>
-for a convenient way to fail if the running Perl interpreter is too old.
-
-Mnemonic: Is this version of perl in the right bracket?
-
-=back
-
-=cut