| Variable |
Meaning |
| $ARGV |
Name of the current file when reading from . |
| @ARGV |
The array containing the command line arguments of the script.
Note that $#ARGV is generally the number of arguments minus one,
since $ARGV[0] is the first argument, not the command name.
See $0 for command name. |
| @INC |
The array containing the list of places to look for Perl scripts
to be evaluated by the do EXPR, require, or use
constructs. It initially consists of the arguments to any -I
command line switches, followed by the default Perl libraries, such as:
/usr/locallib/perl5/$ARCH/$VERSION
/usr/locallib/perl5
/usr/locallib/perl5/site_perl
/usr/locallib/perl5/site_perl/$ARCH
followed by ".", to represent the current directory. In order to modify
this list at run-time, use the lib module in order to get the machine
dependent library loaded:
use lib '/mypath/libdir/';
use SomeMod;
|
| @F |
The array into which the input lines are split when the -a
command line switch is given. |
| %INC |
The hash containing entries for teh filename of each file that
has been included via a do or require. The key is the
filename you specified, and the value is the location of the file
actually found. The require command uses this array to
determine whether a given file has already been included. |
| %ENV |
The hash containing the current environment. Setting a value in
%ENV changes the enviornment for child processes. To remove
something from the enviornment use delete instead if undef.
Note that processes running as a crontab entry inherit a
partiuclarly impoverished set of environment variables. Also note that
you should set $ENV{PATH}, $ENV{SHELL}, and $ENV{IFS} if you are
running as a setuid script. |
| %SIG |
The hash used to get signal handlers for various signals. Example:
sub handler { # 1st argument is signal name
local($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
The %SIG array only contains values for the signals actually
set within the Perl script. Here are some other examples:
$SIG(PIPE) = Plumber; # SCARY!
$SIG(PIPE) = "Plumber"; # fine, assumes main::Plumber
$SIG(PIPE) = \&Plumber; # fine, assume current Plumber
$SIG(PIPE) = Plumber(); # oops, what did Plumber() return?
The example marked SCARY! is problematic because it's a bareword,
which means sometimes it's a string representing the function, and
sometimes it's going to call the subroutine right then and there!
Best to besure and quote it or take a reference to it. Certain
internal hooks can also be set using the %SIG hash. The
routine indicated by $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. One 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;
The routine indicated by $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 teh hook, unless the hook routine itself exist via a goto,
a loop exit, or a die. The __DIE__ handler is explicitly
disabled during the call, so that you youself can then call the
real di from a __DIE__ handler (which avoids an infinite
recursive sequence; same for __WARN__).
|