If you use KDE4, DBus can be used like this:

#!/bin/env perl

use strict;
use warnings;
use Net::DBus;
#use Net::DBus::Dumper;

my $bus = Net::DBus->session;

my $mixer = eval {
    $bus->get_service('org.kde.kmix')->get_object('/Mixers/0/Master_0'
+);
};
if ( $@ ) {
    die "Error: $@.\n";
}
#print dbus_dump($mixer);

$mixer->toggleMute;
#$mixer->decreaseVolume;
#$mixer->increaseVolume;
[download]

I suppose it can be adapted for other desktops also.

Stefan