=head1 DESCRIPTION
-=head2 Predefined Names
+=head2 The Syntax of Variable Names
-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>. In general, it's best to use the
-
- use English '-no_match_vars';
-
-invocation if you don't need $PREMATCH, $MATCH, or $POSTMATCH, as it avoids
-a certain performance hit with the use of regular expressions. See
-L<English>.
-
-Variables that depend on the currently selected filehandle may be set by
-calling an appropriate object method on the 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 IO::Handle attribute.
-The methods each take an optional EXPR, which, if supplied, specifies the
-new value for the IO::Handle attribute in question. If not supplied,
-most methods do nothing to the current value--except for
-autoflush(), which will assume a 1 for you, just to be different.
-
-Because loading in the 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.
+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>.
-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:
+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.
- my $content = '';
- open my $fh, "foo" or die $!;
- {
- local $/;
- $content = <$fh>;
- }
- close $fh;
+Since Perl v5.6.0, Perl variable names may be alphanumeric
+strings that begin with control characters (or better yet, a caret).
+These variables must be written in the form C<${^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.
-Here is an example of how your own code can go broken:
+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:
- for (1..5){
- nasty_break();
- print "$_ ";
- }
- sub nasty_break {
- $_ = 5;
- # do something with $_
- }
+ ENV STDIN
+ INC STDOUT
+ ARGV STDERR
+ ARGVOUT
+ SIG
-You probably expect this code to print:
+In particular, the special C<${^_XYZ}> variables are always taken
+to be in package C<main>, regardless of any C<package> declarations
+presently in scope.
- 1 2 3 4 5
+=head1 SPECIAL VARIABLES
-but instead you get:
+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:
- 5 5 5 5 5
+ use English;
-Why? Because nasty_break() modifies C<$_> without localizing it
-first. The fix is to add local():
+at the top of your program. This aliases all the short names to the long
+names in the current package. Some even have medium names, generally
+borrowed from B<awk>. To avoid a performance hit, if you don't need the
+C<$PREMATCH>, C<$MATCH>, or C<$POSTMATCH> it's best to use the C<English>
+module without them:
- local $_ = 5;
+ use English '-no_match_vars';
-It's easy to notice the problem in such a short example, but in more
-complicated code you are looking for trouble if you don't localize
-changes to the special variables.
+Before you continue, note the sort order for variables. In general, we
+first list the variables in case-insensitive, almost-lexigraphical
+order (ignoring the C<{> or C<^> preceding words, as in C<${^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.
-The following list is ordered by scalar variables first, then the
-arrays, then the hashes.
+=head2 General Variables
=over 8
=item $ARG
=item $_
+X<$_> X<$ARG>
The default input and pattern-searching space. The following pairs are
equivalent:
- while (<>) {...} # equivalent only in while!
+ while (<>) {...} # equivalent only in while!
while (defined($_ = <>)) {...}
/^Subject:/
chomp
chomp($_)
-Here are the places where Perl will assume $_ even if you
-don't use it:
+Here are the places where Perl will assume C<$_> even if you don't use it:
=over 3
=item *
-Various unary functions, including functions like ord() and int(), as well
-as the all file tests (C<-f>, C<-d>) except for C<-t>, which defaults to
-STDIN.
+The following functions use C<$_> as a default argument:
+
+abs, alarm, chomp, chop, chr, chroot,
+cos, defined, eval, evalbytes, exp, fc, glob, hex, int, lc,
+lcfirst, length, log, lstat, mkdir, oct, ord, pos, print, printf,
+quotemeta, readlink, readpipe, ref, require, reverse (in scalar context only),
+rmdir, say, sin, split (for its second
+argument), sqrt, stat, study, uc, ucfirst,
+unlink, unpack.
=item *
-Various list functions like print() and unlink().
+All file tests (C<-f>, C<-d>) except for C<-t>, which defaults to STDIN.
+See L<perlfunc/-X>
=item *
-The pattern matching operations C<m//>, C<s///>, and C<tr///> when used
-without an C<=~> operator.
+The pattern matching operations C<m//>, C<s///> and C<tr///> (aka C<y///>)
+when used without an C<=~> operator.
=item *
=item *
-The implicit iterator variable in the grep() and map() functions.
+The implicit iterator variable in the C<grep()> and C<map()> functions.
=item *
-The default place to put an input record when a C<< <FH> >>
+The implicit variable of C<given()>.
+
+=item *
+
+The default place to put the next value or input record
+when a C<< <FH> >>, C<readline>, C<readdir> or C<each>
operation's result is tested by itself as the sole criterion of a C<while>
test. Outside a C<while> test, this will not happen.
=back
-As C<$_> is a global variable, this may lead in some cases to unwanted
-side-effects. As of perl 5.9.1, you can now use a lexical version of
+C<$_> is by default a global variable. However, as
+of perl v5.10.0, you can use a lexical version of
C<$_> 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.
+declaring C<our $_> restores the global C<$_> in the current scope. Though
+this seemed like a good idea at the time it was introduced, lexical C<$_>
+actually causes more problems than it solves. If you call a function that
+expects to be passed information via C<$_>, it may or may not work,
+depending on how the function is written, there not being any easy way to
+solve this. Just avoid lexical C<$_>, unless you are feeling particularly
+masochistic.
-(Mnemonic: underline is understood in certain operations.)
+Mnemonic: underline is understood in certain operations.
-=back
+=item @ARG
-=over 8
+=item @_
+X<@_> X<@ARG>
-=item $a
+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>.
-=item $b
+See L<perlsub>.
-Special package variables when using sort(), see L<perlfunc/sort>.
-Because of this specialness $a and $b don't need to be declared
-(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.
+=item $LIST_SEPARATOR
-=back
+=item $"
+X<$"> X<$LIST_SEPARATOR>
-=over 8
+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:
-=item $<I<digits>>
+ print "The array is: @array\n";
-Contains the subpattern from the corresponding set of capturing
-parentheses from the last pattern match, not counting patterns
-matched in nested blocks that have been exited already. (Mnemonic:
-like \digits.) These variables are all read-only and dynamically
-scoped to the current BLOCK.
+is equivalent to this:
-=item $MATCH
+ print "The array is: " . join($", @array) . "\n";
-=item $&
+Mnemonic: works in double-quoted context.
-The string matched by the last successful pattern match (not counting
-any matches hidden within a BLOCK or eval() enclosed by the current
-BLOCK). (Mnemonic: like & in some editors.) This variable is read-only
-and dynamically scoped to the current BLOCK.
+=item $PROCESS_ID
-The use of this variable anywhere in a program imposes a considerable
-performance penalty on all regular expression matches. See L</BUGS>.
+=item $PID
-=item $PREMATCH
+=item $$
+X<$$> X<$PID> X<$PROCESS_ID>
-=item $`
+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.
-The string preceding whatever was matched by the last successful
-pattern match (not counting any matches hidden within a BLOCK or eval
-enclosed by the current BLOCK). (Mnemonic: C<`> often precedes a quoted
-string.) This variable is read-only.
+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).
-The use of this variable anywhere in a program imposes a considerable
-performance penalty on all regular expression matches. See L</BUGS>.
+LinuxThreads is now obsolete on Linux, 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.
-=item $POSTMATCH
+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.
-=item $'
+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.
-The string following whatever was matched by the last successful
-pattern match (not counting any matches hidden within a BLOCK or eval()
-enclosed by the current BLOCK). (Mnemonic: C<'> often follows a quoted
-string.) Example:
+Mnemonic: same as shells.
- local $_ = 'abcdefghi';
- /def/;
- print "$`:$&:$'\n"; # prints abc:def:ghi
+=item $PROGRAM_NAME
-This variable is read-only and dynamically scoped to the current BLOCK.
+=item $0
+X<$0> X<$PROGRAM_NAME>
-The use of this variable anywhere in a program imposes a considerable
-performance penalty on all regular expression matches. See L</BUGS>.
+Contains the name of the program being executed.
-=item $LAST_PAREN_MATCH
+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.
-=item $+
+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<$0>.
-The text matched by the last bracket of the last successful search pattern.
-This is useful if you don't know which one of a set of alternative patterns
-matched. For example:
+In some platforms there may be arbitrary amount of padding, for
+example space characters, after the modified name as shown by C<ps>.
+In some platforms this padding may extend all the way to the original
+length of the argument area, no matter what you do (this is the case
+for example with Linux 2.2).
- /Version: (.*)|Revision: (.*)/ && ($rev = $+);
+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.
-(Mnemonic: be positive and forward looking.)
-This variable is read-only and dynamically scoped to the current BLOCK.
+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 $^N
+If the program has been given to perl via the switches C<-e> or C<-E>,
+C<$0> will contain the string C<"-e">.
-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. (Mnemonic: the (possibly) Nested parenthesis that most
-recently closed.)
+On Linux as of perl v5.14.0 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.
-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
+Mnemonic: same as B<sh> and B<ksh>.
- (?:(...)(?{ $var = $^N }))
+=item $REAL_GROUP_ID
-By setting and then using C<$var> in this way relieves you from having to
-worry about exactly which numbered set of parentheses they are.
+=item $GID
-This variable is dynamically scoped to the current BLOCK.
+=item $(
+X<$(> X<$GID> X<$REAL_GROUP_ID>
-=item @LAST_MATCH_END
+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.
-=item @+
+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.
-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 $1 ends, C<$+[2]> the offset
-past where $2 ends, and so on. You can use C<$#+> to determine
-how many subgroups were in the last successful match. See the
-examples given for the C<@-> variable.
+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.
-=item HANDLE->input_line_number(EXPR)
+Mnemonic: parentheses are used to I<group> things. The real gid is the
+group you I<left>, if you're running setgid.
-=item $INPUT_LINE_NUMBER
+=item $EFFECTIVE_GROUP_ID
-=item $NR
+=item $EGID
-=item $.
+=item $)
+X<$)> X<$EGID> X<$EFFECTIVE_GROUP_ID>
-Current line number for the last filehandle accessed.
+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.
-Each filehandle in Perl counts the number of lines that have been read
-from it. (Depending on the value of C<$/>, Perl's idea of what
-constitutes a line may not match yours.) When a line is read from a
-filehandle (via readline() or C<< <> >>), or when tell() or seek() is
-called on it, C<$.> becomes an alias to the line counter for that
-filehandle.
+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< $) = "5 5" >.
-You can adjust the counter by assigning to C<$.>, 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.
+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<$.> is reset when the filehandle is closed, but B<not> when an open
-filehandle is reopened without an intervening close(). For more
-details, see L<perlop/"IE<sol>O Operators">. Because C<< <> >> never does
-an explicit close, line numbers increase across ARGV files (but see
-examples in L<perlfunc/eof>).
+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()>.
-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: parentheses are used to I<group> things. The effective gid
+is the group that's I<right> for you, if you're running setgid.
-(Mnemonic: many programs use "." to mean the current line number.)
+=item $REAL_USER_ID
-=item IO::Handle->input_record_separator(EXPR)
+=item $UID
-=item $INPUT_RECORD_SEPARATOR
+=item $<
+X<< $< >> X<$UID> X<$REAL_USER_ID>
-=item $RS
+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.
-=item $/
+Mnemonic: it's the uid you came I<from>, if you're running setuid.
-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. (Mnemonic: / delimits
-line boundaries when quoting poetry.)
+=item $EFFECTIVE_USER_ID
- local $/; # enable "slurp" mode
- local $_ = <FH>; # whole file now here
- s/\n[ \t]+/ /g;
+=item $EUID
-Remember: the value of C<$/> is a string, not a regex. B<awk> has to be
-better for something. :-)
+=item $>
+X<< $> >> X<$EUID> X<$EFFECTIVE_USER_ID>
-Setting C<$/> 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:
+The effective uid of this process. For example:
- local $/ = \32768; # or \"32768", or \$var_containing_32768
- open my $fh, $myfile or die $!;
- local $_ = <$fh>;
+ $< = $>; # set real to effective uid
+ ($<,$>) = ($>,$<); # swap real and effective uids
-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.
+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.
-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
-file. (This is unlikely to be a problem, because any file you'd
-want to read in record mode is probably unusable in line mode.)
-Non-VMS systems do normal I/O, so it's safe to mix record and
-non-record reads of a file.
+C<< $< >> and C<< $> >> can be swapped only on machines
+supporting C<setreuid()>.
-See also L<perlport/"Newlines">. Also see C<$.>.
+Mnemonic: it's the uid you went I<to>, if you're running setuid.
-=item HANDLE->autoflush(EXPR)
+=item $SUBSCRIPT_SEPARATOR
-=item $OUTPUT_AUTOFLUSH
+=item $SUBSEP
-=item $|
+=item $;
+X<$;> X<$SUBSEP> X<SUBSCRIPT_SEPARATOR>
-If set to nonzero, forces a flush right away and after every write
-or print on the currently selected output channel. Default is 0
-(regardless of whether the channel is really buffered by the
-system or not; C<$|> 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. (Mnemonic: when you want your pipes to be piping hot.)
+The subscript separator for multidimensional array emulation. If you
+refer to a hash element as
-=item IO::Handle->output_field_separator EXPR
+ $foo{$a,$b,$c}
-=item $OUTPUT_FIELD_SEPARATOR
+it really means
-=item $OFS
+ $foo{join($;, $a, $b, $c)}
-=item $,
+But don't put
-The output field separator for the print operator. If defined, this
-value is printed between each of print's arguments. Default is C<undef>.
-(Mnemonic: what is printed when there is a "," in your print statement.)
+ @foo{$a,$b,$c} # a slice--note the @
-=item IO::Handle->output_record_separator EXPR
+which means
-=item $OUTPUT_RECORD_SEPARATOR
+ ($foo{$a},$foo{$b},$foo{$c})
-=item $ORS
+Default is "\034", the same as SUBSEP in B<awk>. If your keys contain
+binary data there might not be any safe value for C<$;>.
-=item $\
+Consider using "real" multidimensional arrays as described
+in L<perllol>.
-The output record separator for the print operator. If defined, this
-value is printed after the last of print's arguments. Default is C<undef>.
-(Mnemonic: you set C<$\> 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.)
+Mnemonic: comma (the syntactic subscript separator) is a semi-semicolon.
-=item $LIST_SEPARATOR
+=item $a
-=item $"
+=item $b
+X<$a> X<$b>
-This is like C<$,> except that it applies to array and slice values
-interpolated into a double-quoted string (or similar interpreted
-string). Default is a space. (Mnemonic: obvious, I think.)
+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 $SUBSCRIPT_SEPARATOR
+=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
+ $SIG{"PIPE"} = Plumber(); # oops, what did Plumber()
+ # return??
+
+Be sure not to use a bareword as the name of a signal handler,
+lest you inadvertently call it.
+
+If your system has the C<sigaction()> function then signal handlers
+are installed using it. This means you get reliable signal handling.
+
+The default delivery policy of signals changed in Perl v5.8.0 from
+immediate (also known as "unsafe") to deferred, also known as "safe
+signals". See L<perlipc> for more information.
+
+Certain internal hooks can be also set using the C<%SIG> hash. The
+routine indicated by C<$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<$PERL_VERSION>
+
+The revision, version, and subversion of the Perl interpreter,
+represented as a C<version> object.
+
+This variable first appeared in perl v5.6.0; earlier versions of perl
+will see an undefined value. Before perl v5.10.0 C<$^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 v5.6.0.
+
+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 v5.10.0.
+
+=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 v5.10.0, 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<$MATCH>
+
+The string matched by the last successful pattern match (not counting
+any matches hidden within a BLOCK or C<eval()> enclosed by the current
+BLOCK).
+
+The use of this variable anywhere in a program imposes a considerable
+performance penalty on all regular expression matches. To avoid this
+penalty, you can extract the same substring by using L</@->. Starting
+with Perl v5.10.0, you can use the C</p> match flag and the C<${^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 v5.10.0.
+
+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 v5.10.0, 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 v5.10.0
+
+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 v5.10.0, 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 v5.10.0.
+
+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 v5.8.0.
+
+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 v5.6.0.
+
+=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<$1> after the following match:
+
+ 'foo' =~ /(?<foo>foo)/;
+
+The keys of the C<%+> hash list only the names of buffers that have
+captured (and that are thus associated to defined values).
+
+The underlying behaviour of C<%+> is provided by the
+L<Tie::Hash::NamedCapture> module.
+
+B<Note:> C<%-> and C<%+> are tied views into a common internal hash
+associated with the last successful regular expression. Therefore mixing
+iterative access to them via C<each> may have unpredictable results.
+Likewise, if the last successful match changes, then the results may be
+surprising.
+
+This variable was added in Perl v5.10.0.
+
+This variable is read-only and dynamically-scoped.
+
+=item @LAST_MATCH_START
+
+=item @-
+X<@-> X<@LAST_MATCH_START>
+
+C<$-[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<@+>.
-=item $SUBSEP
+This array holds the offsets of the beginnings of the last
+successful submatches in the currently active dynamic scope.
+C<$-[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.
-=item $;
+After a match against some variable C<$var>:
-The subscript separator for multidimensional array emulation. If you
-refer to a hash element as
+=over 5
- $foo{$a,$b,$c}
+=item C<$`> is the same as C<substr($var, 0, $-[0])>
-it really means
+=item C<$&> is the same as C<substr($var, $-[0], $+[0] - $-[0])>
- $foo{join($;, $a, $b, $c)}
+=item C<$'> is the same as C<substr($var, $+[0])>
-But don't put
+=item C<$1> is the same as C<substr($var, $-[1], $+[1] - $-[1])>
- @foo{$a,$b,$c} # a slice--note the @
+=item C<$2> is the same as C<substr($var, $-[2], $+[2] - $-[2])>
-which means
+=item C<$3> is the same as C<substr($var, $-[3], $+[3] - $-[3])>
- ($foo{$a},$foo{$b},$foo{$c})
+=back
-Default is "\034", the same as SUBSEP in B<awk>. If your
-keys contain binary data there might not be any safe value for C<$;>.
-(Mnemonic: comma (the syntactic subscript separator) is a
-semi-semicolon. Yeah, I know, it's pretty lame, but C<$,> is already
-taken for something more important.)
+This variable was added in Perl v5.6.0.
+
+=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";
+ }
+ }
+ }
-Consider using "real" multidimensional arrays as described
-in L<perllol>.
+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 v5.10.0.
+
+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 v5.10.0.
+
+=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 v5.10.0.
+
+=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 $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>
-=item $%
+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.
-The current page number of the currently selected output channel.
-Used with formats.
-(Mnemonic: % is page number in B<nroff>.)
+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. Default is 60.
-Used with formats.
-(Mnemonic: = has horizontal lines.)
-
-=item HANDLE->format_lines_left(EXPR)
-
-=item $FORMAT_LINES_LEFT
+output channel. The default is 60.
-=item $-
+Mnemonic: = has horizontal lines.
-The number of lines left on the page of the currently selected output
-channel.
-Used with formats.
-(Mnemonic: lines_on_page - lines_printed.)
+=item HANDLE->format_top_name(EXPR)
-=item @LAST_MATCH_START
+=item $FORMAT_TOP_NAME
-=item @-
+=item $^
+X<$^> X<$FORMAT_TOP_NAME>
-$-[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.
+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>.
-Thus after a match against $_, $& 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<@+>.
+Mnemonic: points to top of page.
-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 $1
-begins, C<$-[2]> the offset where $2 begins, and so on.
+=item HANDLE->format_name(EXPR)
-After a match against some variable $var:
+=item $FORMAT_NAME
-=over 5
+=item $~
+X<$~> X<$FORMAT_NAME>
-=item C<$`> is the same as C<substr($var, 0, $-[0])>
+The name of the current report format for the currently selected
+output channel. The default format name is the same as the filehandle
+name. For example, the default format name for the C<STDOUT>
+filehandle is just C<STDOUT>.
-=item C<$&> is the same as C<substr($var, $-[0], $+[0] - $-[0])>
+Mnemonic: brother to C<$^>.
-=item C<$'> is the same as C<substr($var, $+[0])>
+=back
-=item C<$1> is the same as C<substr($var, $-[1], $+[1] - $-[1])>
+=head2 Error Variables
+X<error> X<exception>
-=item C<$2> is the same as C<substr($var, $-[2], $+[2] - $-[2])>
+The variables C<$@>, 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.
-=item C<$3> is the same as C<substr($var, $-[3], $+[3] - $-[3])>
+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:
-=back
+ eval q{
+ open my $pipe, "/cdrom/install |" or die $!;
+ my @res = <$pipe>;
+ close $pipe or die "bad pipe: $?, $!";
+ };
-=item HANDLE->format_name(EXPR)
+When perl executes the C<eval()> expression, it translates the
+C<open()>, C<< <PIPE> >>, and C<close> calls in the C run-time library
+and thence to the operating system kernel. perl sets C<$!> to
+the C library's C<errno> if one of these calls fails.
-=item $FORMAT_NAME
+C<$@> 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.)
-=item $~
+Under a few operating systems, C<$^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<$^E> the same as C<$!>.
-The name of the current report format for the currently selected output
-channel. Default is the name of the filehandle. (Mnemonic: brother to
-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<$^E>, and C<$?>.
-=item HANDLE->format_top_name(EXPR)
+=over 8
-=item $FORMAT_TOP_NAME
+=item ${^CHILD_ERROR_NATIVE}
+X<$^CHILD_ERROR_NATIVE>
-=item $^
+The native status returned by the last pipe close, backtick (C<``>)
+command, successful call to C<wait()> or C<waitpid()>, or from the
+C<system()> operator. On POSIX-like systems this value can be decoded
+with the WIFEXITED, WEXITSTATUS, WIFSIGNALED, WTERMSIG, WIFSTOPPED,
+WSTOPSIG and WIFCONTINUED functions provided by the L<POSIX> module.
-The name of the current top-of-page format for the currently selected
-output channel. Default is the name of the filehandle with _TOP
-appended. (Mnemonic: points to top of page.)
+Under VMS this reflects the actual VMS exit status; i.e. it is the
+same as C<$?> when the pragma C<use vmsish 'status'> is in effect.
-=item IO::Handle->format_line_break_characters EXPR
+This variable was added in Perl v5.10.0.
-=item $FORMAT_LINE_BREAK_CHARACTERS
+=item $EXTENDED_OS_ERROR
-=item $:
+=item $^E
+X<$^E> X<$EXTENDED_OS_ERROR>
-The current set of characters after which a string may be broken to
-fill continuation fields (starting with ^) in a format. Default is
-S<" \n-">, to break on whitespace or hyphens. (Mnemonic: a "colon" in
-poetry is a part of a line.)
+Error information specific to the current operating system. At the
+moment, this differs from C<$!> under only VMS, OS/2, and Win32 (and
+for MacPerl). On all other platforms, C<$^E> is always just the same
+as C<$!>.
-=item IO::Handle->format_formfeed EXPR
+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>.
-=item $FORMAT_FORMFEED
+Under OS/2, C<$^E> is set to the error code of the last call to OS/2
+API either via CRT, or directly from perl.
-=item $^L
+Under Win32, C<$^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<$^E>. ANSI C and Unix-like calls set C<errno> and so most
+portable Perl code will report errors via C<$!>.
-What formats output as a form feed. Default is \f.
+Caveats mentioned in the description of C<$!> generally apply to
+C<$^E>, also.
-=item $ACCUMULATOR
+This variable was added in Perl 5.003.
-=item $^A
+Mnemonic: Extra error explanation.
-The current value of the write() accumulator for format() lines. A format
-contains formline() calls that put their result into C<$^A>. After
-calling its format, write() prints out the contents of C<$^A> and empties.
-So you never really see the contents of C<$^A> unless you call
-formline() yourself and then look at it. See L<perlform> and
-L<perlfunc/formline()>.
+=item $EXCEPTIONS_BEING_CAUGHT
-=item $CHILD_ERROR
+=item $^S
+X<$^S> X<$EXCEPTIONS_BEING_CAUGHT>
-=item $?
+Current state of the interpreter.
-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
-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:
-similar to B<sh> and B<ksh>.)
+ $^S State
+ --------- -------------------------------------
+ undef Parsing module, eval, or main program
+ true (1) Executing an eval
+ false (0) Otherwise
-Additionally, if the C<h_errno> variable is supported in C, its value
-is returned via $? if any C<gethost*()> function fails.
+The first state may happen in C<$SIG{__DIE__}> and C<$SIG{__WARN__}>
+handlers.
-If you have installed a signal handler for C<SIGCHLD>, the
-value of C<$?> will usually be wrong outside that handler.
+The English name $EXCEPTIONS_BEING_CAUGHT is slightly misleading, because
+the C<undef> value does not indicate whether exceptions are being caught,
+since compilation of the main program does not catch exceptions.
-Inside an C<END> subroutine C<$?> 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:
+This variable was added in Perl 5.004.
- END {
- $? = 1 if $? == 255; # die would make it 255
- }
+=item $WARNING
-Under VMS, the pragma C<use vmsish 'status'> makes C<$?> reflect the
-actual VMS exit status, instead of the default emulation of POSIX
-status; see L<perlvms/$?> for details.
+=item $^W
+X<$^W> X<$WARNING>
-Also see L<Error Indicators>.
+The current value of the warning switch, initially true if B<-w> was
+used, false otherwise, but directly modifiable.
-=item ${^CHILD_ERROR_NATIVE}
+See also L<warnings>.
-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.
+Mnemonic: related to the B<-w> switch.
-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 ${^WARNING_BITS}
+X<${^WARNING_BITS}>
-=item ${^ENCODING}
+The current set of warning checks enabled by the C<use warnings> pragma.
+It has the same scoping as the C<$^H> and C<%^H> variables. The exact
+values are considered internal to the L<warnings> pragma and may change
+between versions of Perl.
-The I<object reference> to the 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. See L<encoding>
-for more details.
+This variable was added in Perl v5.6.0.
=item $OS_ERROR
=item $ERRNO
=item $!
-
-If used numerically, yields the current value of the C C<errno>
-variable, or in other words, if a system or library call fails, it
-sets this variable. This means that the value of C<$!> is meaningful
-only I<immediately> after a B<failure>:
-
- if (open(FH, $filename)) {
- # Here $! is meaningless.
- ...
- } else {
- # ONLY here is $! meaningful.
- ...
- # Already here $! might be meaningless.
+X<$!> 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,
- # here $! is meaningless.
+ # $! is meaningless.
+
+Here, I<meaningless> means that C<$!> 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.
-In the above I<meaningless> stands for anything: zero, non-zero,
-C<undef>. A successful system or library call does B<not> set
-the variable to zero.
+Mnemonic: What just went bang?
-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
-went bang?)
+=item %OS_ERROR
-Also see L<Error Indicators>.
+=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 $!{the_key}>; for a list of legal keys, use C<keys %!>.
-See L<Errno> for more information, and also see above for the
-validity of C<$!>.
-
-=item $EXTENDED_OS_ERROR
-
-=item $^E
+value of C<$!> 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
+$!{the_key}>; for a list of legal keys, use C<keys %!>. See L<Errno>
+for more information, and also see L</$!>.
-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. (Mnemonic: Extra error explanation.)
-
-Also see L<Error Indicators>.
-
-=item $EVAL_ERROR
+This variable was added in Perl 5.005.
-=item $@
+=item $CHILD_ERROR
-The Perl syntax error message from the last eval() operator.
-If $@ is the null string, the last eval() parsed and executed
-correctly (although the operations you invoked may have failed in the
-normal fashion). (Mnemonic: Where was the syntax error "at"?)
+=item $?
+X<$?> X<$CHILD_ERROR>
-Warning messages are not collected in this variable. You can,
-however, set up a routine to process warnings by setting C<$SIG{__WARN__}>
-as described below.
+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<$? & 128> reports whether there was a core dump.
-Also see L<Error Indicators>.
+Additionally, if the C<h_errno> variable is supported in C, its value
+is returned via C<$?> if any C<gethost*()> function fails.
-=item $PROCESS_ID
+If you have installed a signal handler for C<SIGCHLD>, the
+value of C<$?> will usually be wrong outside that handler.
-=item $PID
+Inside an C<END> subroutine C<$?> 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:
-=item $$
+ END {
+ $? = 1 if $? == 255; # die would make it 255
+ }
-The process number of the Perl running this script. You should
-consider this variable read-only, although it will be altered
-across fork() calls. (Mnemonic: same as shells.)
+Under VMS, the pragma C<use vmsish 'status'> makes C<$?> reflect the
+actual VMS exit status, instead of the default emulation of POSIX
+status; see L<perlvms/$?> for details.
-Note for Linux users: on Linux, the C functions C<getpid()> and
-C<getppid()> return different values from different threads. In order to
-be portable, this behavior is not reflected by C<$$>, whose value remains
-consistent across threads. If you want to call the underlying C<getpid()>,
-you may use the CPAN module C<Linux::Pid>.
+Mnemonic: similar to B<sh> and B<ksh>.
-=item $REAL_USER_ID
+=item $EVAL_ERROR
-=item $UID
+=item $@
+X<$@> X<$EVAL_ERROR>
-=item $<
+The Perl syntax error message from the
+last C<eval()> operator. If C<$@> is
+the null string, the last C<eval()> parsed and executed correctly
+(although the operations you invoked may have failed in the normal
+fashion).
-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(). Since
-changes to $< require a system call, check $! after a change attempt to
-detect any possible errors.
+Warning messages are not collected in this variable. You can, however,
+set up a routine to process warnings by setting C<$SIG{__WARN__}> as
+described in L</%SIG>.
-=item $EFFECTIVE_USER_ID
+Mnemonic: Where was the syntax error "at"?
-=item $EUID
+=back
-=item $>
+=head2 Variables related to the interpreter state
-The effective uid of this process. Example:
+These variables provide information about the current interpreter state.
- $< = $>; # set real to effective uid
- ($<,$>) = ($>,$<); # swap real and effective uid
+=over 8
-You can change both the effective uid and the real uid at the same
-time by using POSIX::setuid(). Changes to $> require a check to $!
-to detect any possible errors after an attempted change.
+=item $COMPILING
-(Mnemonic: it's the uid you went I<to>, if you're running setuid.)
-C<< $< >> and C<< $> >> can be swapped only on machines
-supporting setreuid().
+=item $^C
+X<$^C> X<$COMPILING>
-=item $REAL_GROUP_ID
+The current value of the flag associated with the B<-c> switch.
+Mainly of use with B<-MO=...> to allow code to alter its behavior
+when being compiled, such as for example to C<AUTOLOAD> at compile
+time rather than normal, deferred loading. Setting
+C<$^C = 1> is similar to calling C<B::minus_c>.
-=item $GID
+This variable was added in Perl v5.6.0.
-=item $(
+=item $DEBUGGING
-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
-getgid(), and the subsequent ones by getgroups(), one of which may be
-the same as the first number.
+=item $^D
+X<$^D> X<$DEBUGGING>
-However, a value assigned to C<$(> 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.
+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">.
-You can change both the real gid and the effective gid at the same
-time by using POSIX::setgid(). Changes to $( require a check to $!
-to detect any possible errors after an attempted change.
+Mnemonic: value of B<-D> switch.
-(Mnemonic: parentheses are used to I<group> things. The real gid is the
-group you I<left>, if you're running setgid.)
+=item ${^ENCODING}
+X<${^ENCODING}>
-=item $EFFECTIVE_GROUP_ID
+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.
-=item $EGID
+This variable was added in Perl 5.8.2.
-=item $)
+=item ${^GLOBAL_PHASE}
+X<${^GLOBAL_PHASE}>
-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 getegid(), and the subsequent ones by getgroups(), one of
-which may be the same as the first number.
+The current phase of the perl interpreter.
-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 setgroups(). To get the effect of an
-empty list for setgroups(), just repeat the new effective gid; that is,
-to force an effective gid of 5 and an effectively empty setgroups()
-list, say C< $) = "5 5" >.
+Possible values are:
-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.
+=over 8
-(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 CONSTRUCT
-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 setregid().
+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 $PROGRAM_NAME
+=item START
-=item $0
+This is the global compile-time. That includes, basically, every
+C<BEGIN> block executed directly or indirectly from during the
+compile-time of the top-level program.
-Contains the name of the program being executed.
+This phase is not called "BEGIN" to avoid confusion with
+C<BEGIN>-blocks, as those are executed during compile-time of any
+compilation unit, not just the top-level program. A new, localised
+compile-time entered at run-time, for example by constructs as
+C<eval "use SomeModule"> are not global interpreter phases, and
+therefore aren't reflected by C<${^GLOBAL_PHASE}>.
-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>.)
+=item CHECK
-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>.
+Execution of any C<CHECK> blocks.
-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).
+=item INIT
-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.
+Similar to "CHECK", but for C<INIT>-blocks, not C<CHECK> blocks.
-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 RUN
-=item $[
+The main run-time, i.e. the execution of C<PL_main_root>.
-The index of the first element in an array, and of the first character
-in a substring. Default is 0, but you could theoretically set it
-to 1 to make Perl behave more like B<awk> (or Fortran) when
-subscripting and when evaluating the index() and substr() functions.
-(Mnemonic: [ begins subscripts.)
+=item END
-As of release 5 of Perl, assignment to C<$[> 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.
+Execution of any C<END> blocks.
-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 DESTRUCT
-=item $]
+Global destruction.
-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. (Mnemonic: Is this version
-of perl in the right bracket?) Example:
+=back
- warn "No checksumming!\n" if $] < 3.019;
+Also note that there's no value for UNITCHECK-blocks. That's because
+those are run for each compilation unit individually, and therefore is
+not a global interpreter phase.
-See also the documentation of C<use VERSION> and C<require VERSION>
-for a convenient way to fail if the running Perl interpreter is too old.
+Not every program has to go through each of the possible phases, but
+transition from one phase to another can only happen in the order
+described in the above list.
-The floating point representation can sometimes lead to inaccurate
-numeric comparisons. See C<$^V> for a more modern representation of
-the Perl version that allows accurate string comparisons.
+An example of all of the phases Perl code can see:
-=item $COMPILING
+ BEGIN { print "compile-time: ${^GLOBAL_PHASE}\n" }
-=item $^C
+ INIT { print "init-time: ${^GLOBAL_PHASE}\n" }
-The current value of the flag associated with the B<-c> switch.
-Mainly of use with B<-MO=...> to allow code to alter its behavior
-when being compiled, such as for example to AUTOLOAD at compile
-time rather than normal, deferred loading. See L<perlcc>. Setting
-C<$^C = 1> is similar to calling C<B::minus_c>.
+ CHECK { print "check-time: ${^GLOBAL_PHASE}\n" }
-=item $DEBUGGING
+ {
+ package Print::Phase;
-=item $^D
+ sub new {
+ my ($class, $time) = @_;
+ return bless \$time, $class;
+ }
-The current value of the debugging flags. (Mnemonic: value of B<-D>
-switch.) May be read or set. Like its command-line equivalent, you can use
-numeric or symbolic values, eg C<$^D = 10> or C<$^D = "st">.
+ sub DESTROY {
+ my $self = shift;
+ print "$$self: ${^GLOBAL_PHASE}\n";
+ }
+ }
-=item ${^RE_DEBUG_FLAGS}
+ print "run-time: ${^GLOBAL_PHASE}\n";
-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.
+ my $runtime = Print::Phase->new(
+ "lexical variables are garbage collected before END"
+ );
-=item ${^RE_TRIE_MAXBUF}
+ END { print "end-time: ${^GLOBAL_PHASE}\n" }
-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.
+ our $destruct = Print::Phase->new(
+ "package variables are garbage collected after END"
+ );
-=item $SYSTEM_FD_MAX
+This will print out
-=item $^F
+ compile-time: START
+ check-time: CHECK
+ init-time: INIT
+ run-time: RUN
+ lexical variables are garbage collected before END: RUN
+ end-time: END
+ package variables are garbage collected after END: DESTRUCT
-The maximum system file descriptor, ordinarily 2. System file
-descriptors are passed to exec()ed processes, while higher file
-descriptors are not. Also, during an open(), system file descriptors are
-preserved even if the open() fails. (Ordinary file descriptors are
-closed before the open() is attempted.) The close-on-exec
-status of a file descriptor will be decided according to the value of
-C<$^F> when the corresponding file, pipe, or socket was opened, not the
-time of the exec().
+This variable was added in Perl 5.14.0.
=item $^H
+X<$^H>
-WARNING: This variable is strictly for internal use only. Its availability,
+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
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 $^H is saved, but its value is left unchanged.
+block), the existing value of C<$^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 $^H.
+executes within BEGIN blocks is free to change the value of C<$^H>.
This behavior provides the semantic of lexical scoping, and is used in,
for instance, the C<use strict> pragma.
}
Consider what happens during execution of the BEGIN block. At this point
-the BEGIN block has already been compiled, but the body of foo() is still
-being compiled. The new value of $^H will therefore be visible only while
-the body of foo() is being compiled.
+the BEGIN block has already been compiled, but the body of C<foo()> is still
+being compiled. The new value of C<$^H>
+will therefore be visible only while
+the body of C<foo()> is being compiled.
-Substitution of the above BEGIN block with:
+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 }
-
-=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.
-
-=item $INPLACE_EDIT
-
-=item $^I
-
-The current value of the inplace-edit extension. Use C<undef> to disable
-inplace editing. (Mnemonic: value of B<-i> switch.)
-
-=item $^M
-
-By default, running out of memory is an untrappable, fatal error.
-However, if suitably built, Perl can use the contents of C<$^M>
-as an emergency memory pool after die()ing. Suppose that your Perl
-were compiled with C<-DPERL_EMERGENCY_SBRK> and used Perl's malloc.
-Then
-
- $^M = 'a' x (1 << 16);
+demonstrates how C<use strict 'vars'> is implemented. Here's a conditional
+version of the same lexical pragma:
-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.
+ BEGIN {
+ require strict; strict->import('vars') if $condition
+ }
-=item $OSNAME
+This variable was added in Perl 5.003.
-=item $^O
+=item %^H
+X<%^H>
-The name of the operating system under which this copy of Perl was
-built, as determined during the configuration process. The value
-is identical to C<$Config{'osname'}>. See also L<Config> and the
-B<-V> command-line switch documented in L<perlrun>.
+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>.
-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/.NET. Use Win32::GetOSName() or
-Win32::GetOSVersion() (see L<Win32> and L<perlport>) to distinguish
-between the variants.
+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 v5.6.0.
=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 v5.8.0.
+
=item $PERLDB
=item $^P
+X<$^P> X<$PERLDB>
The internal variable for debugging support. The meanings of the
various bits are subject to change, but currently indicate:
=item 0x02
-Line-by-line debugging.
+Line-by-line debugging. Causes C<DB::DB()> subroutine to be called for
+each statement executed. Also causes saving source code lines (like
+0x400).
=item 0x04
=item 0x400
-Debug assertion subroutines enter/exit.
+Save source code lines into C<@{"_<$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.
-
-=item $LAST_REGEXP_CODE_RESULT
-
-=item $^R
-
-The result of evaluation of the last successful C<(?{ code })>
-regular expression assertion (see L<perlre>). May be written to.
-
-=item $EXCEPTIONS_BEING_CAUGHT
-
-=item $^S
-
-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 $^T
-
-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.
+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.
+B<-t> or B<-TU>).
+
+This variable is read-only.
+
+This variable was added in Perl v5.8.0.
=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.
+the possible values.
+
+This variable is set during Perl startup and is thereafter read-only.
+
+This variable was added in Perl v5.8.2.
=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 v5.8.9.
+
=item ${^UTF8LOCALE}
+X<${^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
+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.
-=item $PERL_VERSION
-
-=item $^V
-
-The revision, version, and subversion of the Perl interpreter, represented
-as a string composed of characters with those ordinals. Thus in Perl v5.6.0
-it equals C<chr(5) . chr(6) . chr(0)> and will return true for
-C<$^V eq v5.6.0>. Note that the characters in this string value can
-potentially be in Unicode range.
-
-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 $^V lt v5.6.0;
-
-To convert C<$^V> into its string representation use 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.
-
-=item $WARNING
-
-=item $^W
-
-The current value of the warning switch, initially true if B<-w>
-was used, false otherwise, but directly modifiable. (Mnemonic:
-related to the B<-w> switch.) See also L<warnings>.
-
-=item ${^WARNING_BITS}
-
-The current set of warning checks enabled by the C<use warnings> pragma.
-See the documentation of C<warnings> for more details.
-
-=item $EXECUTABLE_NAME
-
-=item $^X
-
-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 $^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 $^X is in PATH. For VMS, the
-value may or may not include a version number.
-
-You usually can use the value of $^X to re-invoke an independent
-copy of the same perl that is currently running, e.g.,
-
- @first_run = `$^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 $^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 $^X to a path name, use the
-following statements:
-
- # Build up a set of file names (not command names).
- use Config;
- $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 $^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;
- $secure_perl_path = $Config{perlpath};
- if ($^O ne 'VMS')
- {$secure_perl_path .= $Config{_exe}
- unless $secure_perl_path =~ m/$Config{_exe}$/i;}
-
-=item 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 $ARGV
-
-contains the name of the current file when reading from <>.
-
-=item @ARGV
-
-The array @ARGV contains the command-line arguments intended for
-the script. C<$#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 C<$0> for the command name.
-
-=item ARGVOUT
+This variable was added in Perl v5.8.8.
-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.
+=back
-=item @F
+=head2 Deprecated and removed variables
-The array @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'>.
+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.
-=item @INC
+Once a variable is removed, its use triggers an error telling you
+the variable is unsupported.
-The array @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:
+See L<perldiag> for details about error messages.
- use lib '/mypath/libdir/';
- use SomeMod;
+=over 8
-You can also insert hooks into the file inclusion system by putting Perl
-code directly into @INC. Those hooks may be subroutine references, array
-references or blessed objects. See L<perlfunc/require> for details.
+=item $OFMT
-=item @_
+=item $#
+X<$#> X<$OFMT>
-Within a subroutine the array @_ contains the parameters passed to that
-subroutine. See L<perlsub>.
+C<$#> was a variable that could be used to format printed numbers.
+After a deprecation cycle, its magic was removed in Perl v5.10.0 and
+using it now triggers a warning: C<$# is no longer supported>.
-=item %INC
+This is not the sigil you use in front of an array name to get the
+last index, like C<$#array>. That's still how you get the last index
+of an array in Perl. The two have nothing to do with each other.
-The hash %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.
+Deprecated in Perl 5.
-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 %INC in place of a filename. Note, however,
-that the hook may have set the %INC entry by itself to provide some more
-specific info.
+Removed in Perl v5.10.0.
-=item %ENV
+=item $*
+X<$*>
-=item $ENV{expr}
+C<$*> was a variable that you could use to enable multiline matching.
+After a deprecation cycle, its magic was removed in Perl v5.10.0.
+Using it now triggers a warning: C<$* is no longer supported>.
+You should use the C</s> and C</m> regexp modifiers instead.
-The hash %ENV contains your current environment. Setting a
-value in C<ENV> changes the environment for any child processes
-you subsequently fork() off.
+Deprecated in Perl 5.
-=item %SIG
+Removed in Perl v5.10.0.
-=item $SIG{expr}
+=item $ARRAY_BASE
-The hash %SIG contains signal handlers for signals. For example:
+=item $[
+X<$[> X<$ARRAY_BASE>
- sub handler { # 1st argument is signal name
- my($sig) = @_;
- print "Caught a SIG$sig--shutting down\n";
- close(LOG);
- exit(0);
- }
+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.
- $SIG{'INT'} = \&handler;
- $SIG{'QUIT'} = \&handler;
- ...
- $SIG{'INT'} = 'DEFAULT'; # restore default action
- $SIG{'QUIT'} = 'IGNORE'; # ignore SIGQUIT
+As of release 5 of Perl, assignment to C<$[> 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.
-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.
+Prior to Perl v5.10.0, 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.
-Here are some other examples:
+As of Perl v5.16.0, it is implemented by the L<arybase> module. See
+L<arybase> for more details on its behaviour.
- $SIG{"PIPE"} = "Plumber"; # assumes main::Plumber (not recommended)
- $SIG{"PIPE"} = \&Plumber; # just fine; assume current Plumber
- $SIG{"PIPE"} = *Plumber; # somewhat esoteric
- $SIG{"PIPE"} = Plumber(); # oops, what did Plumber() return??
+Under C<use v5.16>, or C<no feature "array_base">, C<$[> no longer has any
+effect, and always contains 0. Assigning 0 to it is permitted, but any
+other value will produce an error.
-Be sure not to use a bareword as the name of a signal handler,
-lest you inadvertently call it.
+Mnemonic: [ begins subscripts.
-If your system has the sigaction() function then signal handlers are
-installed using it. This means you get reliable signal handling.
+Deprecated in Perl v5.12.0.
-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.
+=item $OLD_PERL_VERSION
-Certain internal hooks can be also set using the %SIG hash. The
-routine indicated by C<$SIG{__WARN__}> is called when a warning message is
-about to be printed. The warning message is passed as the first
-argument. The presence of a __WARN__ hook causes the ordinary printing
-of warnings to STDERR to be suppressed. You can use this to save warnings
-in a variable, or turn warnings into fatal errors, like this:
+=item $]
+X<$]> X<$OLD_PERL_VERSION>
- local $SIG{__WARN__} = sub { die $_[0] };
- eval $proggie;
+See L</$^V> for a more modern representation of the Perl version that allows
+accurate string comparisons.
-The routine indicated by C<$SIG{__DIE__}> is called when a fatal exception
-is about to be thrown. The error message is passed as the first
-argument. When a __DIE__ hook routine returns, the exception
-processing continues as it would have in the absence of the hook,
-unless the hook routine itself exits via a C<goto>, a loop exit, or a die().
-The C<__DIE__> handler is explicitly disabled during the call, so that you
-can die from a C<__DIE__> handler. Similarly for C<__WARN__>.
+The version + patchlevel / 1000 of the Perl interpreter. This variable
+can be used to determine whether the Perl interpreter executing a
+script is in the right range of versions:
-Due to an implementation glitch, the C<$SIG{__DIE__}> hook is called
-even inside an eval(). Do not use this to rewrite a pending exception
-in C<$@>, or as a bizarre substitute for overriding CORE::GLOBAL::die().
-This strange action at a distance may be fixed in a future release
-so that C<$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:
+ warn "No checksumming!\n" if $] < 3.019;
- require Carp if defined $^S;
- Carp::confess("Something wrong") if defined &Carp::confess;
- die "Something wrong, but could not load Carp to give backtrace...
- To see backtrace try starting Perl with -MCarp switch";
+The floating point representation can sometimes lead to inaccurate
+numeric comparisons.
-Here the first line will load Carp I<unless> it is the parser who
-called the handler. The second line will print backtrace and die if
-Carp was available. The third line will be executed only if Carp was
-not available.
+See also the documentation of C<use VERSION> and C<require VERSION>
+for a convenient way to fail if the running Perl interpreter is too old.
-See L<perlfunc/die>, L<perlfunc/warn>, L<perlfunc/eval>, and
-L<warnings> for additional information.
+Mnemonic: Is this version of perl in the right bracket?
=back
-=head2 Error Indicators
-
-The variables C<$@>, 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:
-
- eval q{
- open my $pipe, "/cdrom/install |" or die $!;
- my @res = <$pipe>;
- close $pipe or die "bad pipe: $?, $!";
- };
-
-After execution of this statement all 4 variables may have been set.
-
-C<$@> 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 die()d . In these cases
-the value of $@ is the compile error, or the argument to C<die>
-(which will interpolate C<$!> and C<$?>). (See also L<Fatal>,
-though.)
-
-When the eval() expression above is executed, open(), C<< <PIPE> >>,
-and C<close> are translated to calls in the C run-time library and
-thence to the operating system kernel. C<$!> is set to the C library's
-C<errno> if one of these calls fails.
-
-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 exit()
-value). The lower eight bits reflect mode of failure, like signal
-death and core dump information See 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 eval() is always set on failure and cleared on success.
-
-For more details, see the individual descriptions at C<$@>, C<$!>, C<$^E>,
-and C<$?>.
-
-=head2 Technical Note on 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<$^W> (dollar-sign caret
-C<W>) is the scalar variable whose name is the single character
-control-C<W>. This is better than typing a literal control-C<W>
-into your program.
-
-Finally, new in Perl 5.6, Perl variable names may be alphanumeric
-strings that begin with control characters (or better yet, a caret).
-These variables must be written in the form C<${^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 new special C<${^_XYZ}> variables are always taken
-to be in package C<main>, regardless of any C<package> declarations
-presently in scope.
-
-=head1 BUGS
-
-Due to an unfortunate accident of Perl's implementation, C<use
-English> imposes a considerable performance penalty on all regular
-expression matches in a program, regardless of whether they occur
-in the scope of C<use English>. For that reason, saying C<use
-English> in libraries is strongly discouraged. See the
-Devel::SawAmpersand module documentation from CPAN
-( http://www.cpan.org/modules/by-module/Devel/ )
-for more information.
-
-Having to even think about the C<$^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.
+=cut
https://perl5.git.perl.org / perl5.git / blobdiff