diff options
Diffstat (limited to 'pod/perlvar.pod')
| -rw-r--r-- | pod/perlvar.pod | 103 |
1 files changed, 70 insertions, 33 deletions
diff --git a/pod/perlvar.pod b/pod/perlvar.pod index 6487fdda36..75f4e6d5c2 100644 --- a/pod/perlvar.pod +++ b/pod/perlvar.pod @@ -18,9 +18,9 @@ long names in the current package. Some of them even have medium names, 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; @@ -42,6 +42,12 @@ 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. +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 @@ -438,16 +444,13 @@ 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<$!> again, except under OS/2.) +C<$!>, 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 $@ @@ -597,8 +600,8 @@ C<$^F> at the time of the open, not the time of the exec. =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 @@ -607,6 +610,20 @@ documentation of C<strict> for more details. 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 @@ -653,6 +670,12 @@ Start with single-step on. 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 @@ -699,6 +722,11 @@ to get the machine-dependent library properly loaded also: 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 @@ -707,25 +735,25 @@ specified, and the value is the location of the file actually found. 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 @@ -733,8 +761,8 @@ signals. Example: 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?? @@ -775,21 +803,30 @@ 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__>. 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 |