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

my $open;                          # declare global variable,

my $mw = MainWindow->new();

$mw-> Button( -text =>'Open',           -command => \&open_file )->pack(); 
$mw-> Button( -text =>'Get Statistics', -command => \&get_statistics )->pack(); 

MainLoop();

sub open_file {
    $open = $mw->getOpenFile();    # set it,
}

sub get_statistics {
    my $fastafile = $open;         # and use it.
    print STDERR "selected file: $fastafile\n";
}