Config - access Perl configuration information |
Config - access Perl configuration information
use Config; if (%Config{usethreads}) { print "has thread support\n" }
use Config qw(myconfig config_sh config_vars config_re);
print myconfig();
print config_sh();
print config_re();
config_vars(qw(osname archname));
The Config module contains all the information that was available to
the Configure
program at Perl build time (over 900 values).
Shell variables from the config.sh file (written by Configure) are
stored in the readonly-variable %Config
, indexed by their names.
Values stored in config.sh as 'undef' are returned as undefined
values. The perl exists
function can be used to check if a
named variable exists.
myconfig()
Returns a textual summary of the major perl configuration values.
See also -V
in Switches in the perlrun manpage.
config_sh()
Returns the entire perl configuration information in the form of the original config.sh shell variable assignment script.
config_re($regex)
Like config_sh()
but returns, as a list, only the config entries who's
names match the $regex.
config_vars(@names)
Prints to STDOUT the values of the named configuration variable. Each is printed on a separate line in the form:
name='value';
Names which are unknown are output as name='UNKNOWN';
.
See also -V:name
in Switches in the perlrun manpage.
Here's a more sophisticated example of using %Config:
use Config; use strict;
my %sig_num; my @sig_name; unless(%Config{sig_name} && %Config{sig_num}) { die "No sigs?"; } else { my @names = split ' ', %Config{sig_name}; %sig_num{[@names]} = split ' ', %Config{sig_num}; foreach (@names) { @sig_name[$sig_num{$_}] ||= $_; } }
print "signal #17 = @sig_name[17]\n"; if (%sig_num{ALRM}) { print "SIGALRM is %sig_num{ALRM}\n"; }
Because this information is not stored within the perl executable itself it is possible (but unlikely) that the information does not relate to the actual perl binary which is being used to access it.
The Config module is installed into the architecture and version specific library directory (%Config{installarchlib}) and it checks the perl version number when loaded.
The values stored in config.sh may be either single-quoted or
double-quoted. Double-quoted strings are handy for those cases where you
need to include escape sequences in the strings. To avoid runtime variable
interpolation, any $
and @
characters are replaced by \$
and
\@
, respectively. This isn't foolproof, of course, so don't embed \$
or \@
in double-quoted strings unless you're willing to deal with the
consequences. (The slashes will end up escaped and the $
or @
will
trigger variable interpolation)
Most Config
variables are determined by the Configure
script
on platforms supported by it (which is most UNIX platforms). Some
platforms have custom-made Config
variables, and may thus not have
some of the variables described below, or may have extraneous variables
specific to that particular port. See the port specific documentation
in such cases.
This module contains a good example of how to use tie to implement a cache and an example of how to make a tied variable readonly to those outside of it.
Config - access Perl configuration information |