++ed by:

100 PAUSE users
204 non-PAUSE users.

Gurusamy Sarathy


Config - access Perl configuration information


    use Config;
    if ($Config{'cc'} =~ /gcc/) {
        print "built by gcc\n";

    use Config qw(myconfig config_sh config_vars);

    print myconfig();

    print config_sh();

    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.


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.


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.


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.


    open(GLOS, "<$glossary") or die "Can't open $glossary: $!";

    my ($var,$unit,$indentpara); my $text = ""; while (<GLOS>) { if (/^\s*(.*)\s*\(\s*(.+\.U)\s*\):\s*$/) { print CONFIG "\n=item $var\n\n$text\n" if $var and $text; ($var,$unit,$text) = ($1,$2,""); } else { # bite off exactly one tab-width s/^([ ]{8}|[ ]{0,7}\t)//;

            # indented stuff starts a separate paragraph
            if (/^\s/) {
                $text .= "\n" unless $indentpara;
                $indentpara = 1;
            else {
                $text .= "\n" if $indentpara;
                $indentpara = 0;
            $text .= $_;

    print CONFIG "\n=item $var\n\n$text\n" if $var and $text;

    print CONFIG <<'ENDOFTAIL';


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.