generally borrowed from B<awk>.
To go a step further, those variables that depend on the currently
-selected filehandle may instead be set by calling an object method on
-the FileHandle object. (Summary lines below for this contain the word
-HANDLE.) First you must say
+selected filehandle may instead (and preferably) be set by calling an
+object method on the FileHandle object. (Summary lines below for this
+contain the word HANDLE.) First you must say
use FileHandle;
you try to assign to this variable, either directly or indirectly through
a reference, you'll raise a run-time exception.
+The following list is ordered by scalar variables first, then the
+arrays, then the hashes (except $^M was added in the wrong place).
+This is somewhat obscured by the fact that %ENV and %SIG are listed as
+$ENV{expr} and $SIG{expr}.
+
+
=over 8
=item $ARG
=item $^E
More specific information about the last system error than that provided by
-C<$!>, if available. (If not, it's just C<$!> again, except under OS/2.)
+C<$!>, if available. (If not, it's just C<$!> again.)
At the moment, this differs from C<$!> 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
+code of the last call to OS/2 API either via CRT, or directly from perl. 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
=item $@
=item $^H
-The current set of syntax checks enabled by C<use strict>. See the
-documentation of C<strict> for more details.
+The current set of syntax checks enabled by C<use strict> and other block
+scoped compiler hints. See the documentation of C<strict> for more details.
=item $INPLACE_EDIT
The current value of the inplace-edit extension. Use C<undef> to disable
inplace editing. (Mnemonic: value of B<-i> switch.)
+=item $^M
+
+By default, running out of memory it is not trappable. However, if
+compiled for this, Perl may use the contents of C<$^M> as an emergency
+pool after die()ing with this message. Suppose that your Perl were
+compiled with -DPERL_EMERGENCY_SBRK and used Perl's malloc. Then
+
+ $^M = 'a' x (1<<16);
+
+would allocate a 64K buffer for use when in emergency. See the F<INSTALL>
+file for information on how to enable this option. As a disincentive to
+casual use of this advanced feature, there is no L<English> long name for
+this variable.
+
=item $OSNAME
=item $^O
Note that some bits may be relevent at compile-time only, some at
run-time only. This is a new mechanism and the details may change.
+=item $^S
+
+Current state of the interpreter. Undefined if parsing of the current
+module/eval is not finished (may happen in $SIG{__DIE__} and
+$SIG{__WARN__} handlers). True if inside an eval, othewise false.
+
=item $BASETIME
=item $^T
use lib '/mypath/libdir/';
use SomeMod;
+=item @_
+
+Within a subroutine the array @_ contains the parameters passed to that
+subroutine. See L<perlsub>.
+
=item %INC
The hash %INC contains entries for each filename that has
The C<require> command uses this array to determine whether a given file
has already been included.
-=item $ENV{expr}
+=item %ENV $ENV{expr}
The hash %ENV contains your current environment. Setting a
value in C<ENV> changes the environment for child processes.
-=item $SIG{expr}
+=item %SIG $SIG{expr}
The hash %SIG is used to set signal handlers for various
signals. Example:
sub handler { # 1st argument is signal name
- local($sig) = @_;
+ my($sig) = @_;
print "Caught a SIG$sig--shutting down\n";
close(LOG);
exit(0);
}
- $SIG{'INT'} = 'handler';
- $SIG{'QUIT'} = 'handler';
+ $SIG{'INT'} = \&handler;
+ $SIG{'QUIT'} = \&handler;
...
$SIG{'INT'} = 'DEFAULT'; # restore default action
$SIG{'QUIT'} = 'IGNORE'; # ignore SIGQUIT
The %SIG array contains values for only the signals actually set within
the Perl script. Here are some other examples:
- $SIG{PIPE} = Plumber; # SCARY!!
- $SIG{"PIPE"} = "Plumber"; # just fine, assumes main::Plumber
+ $SIG{"PIPE"} = Plumber; # SCARY!!
+ $SIG{"PIPE"} = "Plumber"; # assumes main::Plumber (not recommended)
$SIG{"PIPE"} = \&Plumber; # just fine; assume current Plumber
$SIG{"PIPE"} = Plumber(); # oops, what did Plumber() return??
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__>. See
-L<perlfunc/die>, L<perlfunc/warn> and L<perlfunc/eval>.
-
-=item $^M
-
-By default, running out of memory it is not trappable. However, if
-compiled for this, Perl may use the contents of C<$^M> as an emergency
-pool after die()ing with this message. Suppose that your Perl were
-compiled with -DPERL_EMERGENCY_SBRK and used Perl's malloc. Then
-
- $^M = 'a' x (1<<16);
-
-would allocate a 64K buffer for use when in emergency. See the F<INSTALL>
-file for information on how to enable this option. As a disincentive to
-casual use of this advanced feature, there is no L<English> long name for
-this variable.
+can die from a C<__DIE__> handler. Similarly for C<__WARN__>.
+
+Note that the C<$SIG{__DIE__}> hook is called even inside eval()ed
+blocks/strings. See L<perlfunc/die>, L<perlvar/$^S> for how to
+circumvent this.
+
+Note that 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 calls which result/may-result
+in parsing Perl should be used with extreme causion, 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...
+ To see backtrace try starting Perl with -MCarp switch";
+
+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 L<perlfunc/die>, L<perlfunc/warn> and L<perlfunc/eval> for
+additional info.
=back
projects / p5sagit/p5-mst-13.2.git / blobdiff