#!/usr/bin/perl
use strict;
use Tk;

sub clicked {
    system ( 'myscript.pl' );
}

my $top = MainWindow->new();
my $button = $top->Button ( 
                           -text => "click me",
                           -command => \&clicked
                          )->pack();
...
MainLoop();

##</code><code>##

my $button = $top->Button ( 
                           -text => "click me",
                           -command => [\&clicked, \$filename]
                          )->pack();