=head2 Predefined Names
The following names have special meaning to Perl. Most of the
-punctuational names have reasonable mnemonics, or analogues in one of
+punctuation names have reasonable mnemonics, or analogues in one of
the shells. Nevertheless, if you wish to use the long variable names,
you just need to say
The default input and pattern-searching space. The following pairs are
equivalent:
- while (<>) {...} # only equivalent in while!
+ while (<>) {...} # equivalent in only while!
while ($_ = <>) {...}
/^Subject:/
=item $E<lt>I<digit>E<gt>
-Contains the subpattern from the corresponding set of parentheses in
+Contains the sub-pattern from the corresponding set of parentheses in
the last pattern matched, not counting patterns matched in nested
blocks that have been exited already. (Mnemonic: like \digit.)
These variables are all read-only.
=item $*
-Set to 1 to do multiline matching within a string, 0 to tell Perl
+Set to 1 to do multi-line matching within a string, 0 to tell Perl
that it can assume that strings contain a single line, for the purpose
of optimizing pattern matches. Pattern matches on strings containing
multiple newlines can produce confusing results when "C<$*>" is 0. Default
is 0. (Mnemonic: * matches multiple things.) Note that this variable
-only influences the interpretation of "C<^>" and "C<$>". A literal newline can
+influences the interpretation of only "C<^>" and "C<$>". A literal newline can
be searched for even when C<$* == 0>.
-Use of "C<$*>" is deprecated in Perl 5.
+Use of "C<$*>" is deprecated in modern perls.
=item input_line_number HANDLE EXPR
The current input line number for the last file handle from
which you read (or performed a C<seek> or C<tell> on). An
-explicit close on a filehandle resets the line number. Since
+explicit close on a filehandle resets the line number. Because
"C<E<lt>E<gt>>" never does an explicit close, line numbers increase
across ARGV files (but see examples under eof()). Localizing C<$.> has
the effect of also localizing Perl's notion of "the last read
If set to nonzero, forces a flush after every write or print on the
currently selected output channel. Default is 0 (regardless of whether
-the channel is actually buffered by the system or not; C<$|> only tells
-you whether you've asked Perl to explicitly flush after each write).
+the channel is actually buffered by the system or not; C<$|> tells you
+only whether you've asked Perl explicitly to flush after each write).
Note that 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, such as when you are running
=item $,
The output field separator for the print operator. Ordinarily the
-print operator simply prints out the comma separated fields you
-specify. In order to get behavior more like B<awk>, set this variable
+print operator simply prints out the comma-separated fields you
+specify. To get behavior more like B<awk>, set this variable
as you would set B<awk>'s OFS variable to specify what is printed
between fields. (Mnemonic: what is printed when there is a , in your
print statement.)
=item $\
The output record separator for the print operator. Ordinarily the
-print operator simply prints out the comma separated fields you
-specify, with no trailing newline or record separator assumed. In
-order to get behavior more like B<awk>, set this variable as you would
+print operator simply prints out the comma-separated fields you
+specify, with no trailing newline or record separator assumed.
+To get behavior more like B<awk>, set this variable as you would
set B<awk>'s ORS variable to specify what is printed at the end of the
print. (Mnemonic: you set "C<$\>" instead of adding \n at the end of the
print. Also, it's just like C<$/>, but it's what you get "back" from
semi-semicolon. Yeah, I know, it's pretty lame, but "C<$,>" is already
taken for something more important.)
-Consider using "real" multi-dimensional arrays in Perl 5.
+Consider using "real" multi-dimensional arrays.
=item $OFMT
B<awk>'s default OFMT setting of %.6g, so you need to set "C<$#>"
explicitly to get B<awk>'s value. (Mnemonic: # is the number sign.)
-Use of "C<$#>" is deprecated in Perl 5.
+Use of "C<$#>" is deprecated.
=item format_page_number HANDLE EXPR
=item $^L
-What formats output to perform a formfeed. Default is \f.
+What formats output to perform a form feed. Default is \f.
=item $ACCUMULATOR
=item $?
-The status returned by the last pipe close, backtick (C<``>) command,
-or system() operator. Note that this is the status word returned by
-the wait() system call, so the exit value of the subprocess is actually
-(C<$? E<gt>E<gt> 8>). Thus on many systems, C<$? & 255> gives which signal,
-if any, the process died from, and whether there was a core dump.
-(Mnemonic: similar to B<sh> and B<ksh>.)
+The status returned by the last pipe close, back-tick (C<``>) command,
+or system() operator. Note that this is the status word returned by the
+wait() system call (or else is made up to look like it -- see L<$^S>).
+Thus, the exit value of the subprocess is actually (C<$? E<gt>E<gt> 8>),
+and C<$? & 255> gives which signal, if any, the process died from, and
+whether there was a core dump. (Mnemonic: similar to B<sh> and B<ksh>.)
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 the script.
+=item $SYSTEM_CHILD_STATUS
+
+=item $^S
+
+The status returned by the last pipe close, back-tick (C<``>) command, or
+system() operator, in the native system format. On UNIX and UNIX-like
+systems, C<$^S> is a synonym for C<$?>. Elsewhere, C<$^S> can be used to
+determine aspects of child status that are system-specific. Check C<$^O>
+before using this variable. (Mnemonic: System-Specific Subprocess Status.)
+
=item $OS_ERROR
=item $ERRNO
value of "C<$!>" to be anything in particular unless you've gotten a
specific error return indicating a system error.) If used in a string
context, yields the corresponding system error string. You can assign
-to "C<$!>" in order to set I<errno> if, for instance, you want "C<$!>" to return the
+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 $^E
-More specific information about the last system error than that
-provided by C<$!>, if available. (If not, it's just C<$!> again.)
-At the moment, this differs from C<$!> only under VMS, where it
-provides the VMS status value from the last system error. The
+More specific information about the last system error than that provided by
+C<$!>, if available. (If not, it's just C<$!> again, except under OS/2.)
+At the moment, this differs from C<$!> under only VMS and OS/2, where it
+provides the VMS status value from the last system error, and OS/2 error
+code of the last call to OS/2 API which was not directed via CRT. The
caveats mentioned in the description of C<$!> apply here, too.
(Mnemonic: Extra error explanation.)
+Note that under OS/2 C<$!> and C<$^E> do not track each other, so if an
+OS/2-specific call is performed, you may need to check both.
=item $EVAL_ERROR
($<,$>) = ($>,$<); # swap real and effective uid
(Mnemonic: it's the uid you went I<TO>, if you're running setuid.) Note:
-"C<$E<lt>>" and "C<$E<gt>>" can only be swapped on machines supporting setreuid().
+"C<$E<lt>>" and "C<$E<gt>>" can be swapped on only machines supporting setreuid().
=item $REAL_GROUP_ID
used to I<GROUP> things. The effective gid is the group that's I<RIGHT> for
you, if you're running setgid.)
-Note: "C<$E<lt>>", "C<$E<gt>>", "C<$(>" and "C<$)>" can only be set on machines
-that support the corresponding I<set[re][ug]id()> routine. "C<$(>" and "C<$)>"
-can only be swapped on machines supporting setregid(). Because Perl doesn't
-currently use initgroups(), you can't set your group vector to multiple groups.
+Note: "C<$E<lt>>", "C<$E<gt>>", "C<$(>" and "C<$)>" can be set only on
+machines that support the corresponding I<set[re][ug]id()> routine. "C<$(>"
+and "C<$)>" can be swapped on only machines supporting setregid(). Because
+Perl doesn't currently use initgroups(), you can't set your group vector to
+multiple groups.
=item $PROGRAM_NAME
=item $^T
The time at which the script began running, in seconds since the
-epoch (beginning of 1970). The values returned by the B<-M>, B<-A>
+epoch (beginning of 1970). The values returned by the B<-M>, B<-A>,
and B<-C> filetests are
based on this value.
The array @ARGV contains the command line arguments intended for the
script. Note that C<$#ARGV> is the generally number of arguments minus
-one, since C<$ARGV[0]> is the first argument, I<NOT> the command name. See
+one, because C<$ARGV[0]> is the first argument, I<NOT> the command name. See
"C<$0>" for the command name.
=item @INC
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. If you need to
-modify this at runtime, you should use the C<use lib> pragma in order
-to also get the machine-dependent library properly loaded:
+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;
$SIG{'INT'} = 'DEFAULT'; # restore default action
$SIG{'QUIT'} = 'IGNORE'; # ignore SIGQUIT
-The %SIG array only contains values for the signals actually set within
+The %SIG array contains values for only the signals actually set within
the Perl script. Here are some other examples:
$SIG{PIPE} = Plumber; # SCARY!!
going to call the subroutine call right then and there! Best to be sure
and quote it or take a reference to it. *Plumber works too. See L<perlsub>.
+If your system has the sigaction() function then signal handlers are
+installed using it. This means you get reliable signal handling. If
+your system has the SA_RESTART flag it is used when signals handlers are
+installed. This means that system calls for which it is supported
+continue rather than returning when a signal arrives. If you want your
+system calls to be interrupted by signal delivery then do something like
+this:
+
+ use POSIX ':signal_h';
+
+ my $alarm = 0;
+ sigaction SIGALRM, new POSIX::SigAction sub { $alarm = 1 }
+ or die "Error setting SIGALRM handler: $!\n";
+
+See L<POSIX>.
+
Certain internal hooks can be also set using the %SIG hash. The
routine indicated by C<$SIG{__WARN__}> is called when a warning message is
about to be printed. The warning message is passed as the first
argument. 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 __DIE__ handler is explicitly disabled during the call, so that you
-can die from a __DIE__ handler. Similarly for __WARN__.
+The C<__DIE__> handler is explicitly disabled during the call, so that you
+can die from a C<__DIE__> handler. Similarly for C<__WARN__>. See
+L<perlfunc/die>, L<perlfunc/warn> and L<perlfunc/eval>.
=back
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