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Author image David A P Mitchell
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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.

For a description of the variables, please have a look at the Glossary file, as written in the Porting folder, or use the url: http://perl5.git.perl.org/perl.git/blob/HEAD:/Porting/Glossary


Returns a textual summary of the major perl configuration values. See also -V in "Switches" in perlrun.


Returns the entire perl configuration information in the form of the original config.sh shell variable assignment script.


Like config_sh() but returns, as a list, only the config entries who's names match the $regex.


Prints to STDOUT the values of the named configuration variable. Each is printed on a separate line in the form:


Names which are unknown are output as name='UNKNOWN';. See also -V:name in "Switches" in perlrun.


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.



Information on the git commit from which the current perl binary was compiled can be found in the variable $Config::Git_Data. The variable is a structured string that looks something like this:

  git_commit_id_title='Commit id:'
  git_commit_date='2009-05-09 17:47:31 +0200'

Its format is not guaranteed not to change over time.


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.

1 POD Error

The following errors were encountered while parsing the POD:

Around line 880:

=back without =over