Entry Widget - validatecommand

[shortyfw06]

I'm trying to set a validate command allowing for only positive or negative integers. I also want a reset button to clear the entry. This doesn't seem to be working properly. Can anyone offer some advice? Thanks.

#!usr/bin/perl
use Tk;
use strict;
use warnings;
#
my $value;
my $mw=new MainWindow;
my $ent = $mw -> Entry(-textvariable=> \$value,
    -validate=>'key',
    -validatecommand=>sub { $_[0] =~ /-{0,1}\d+$/ },
    -invalidcommand=> \&lam_num_error)->pack();
my $print_button = $mw->Button(-text=>"Print",
    -command=> \&print, -font=>"ansi 10 bold")->pack();
#
my $reset_frm = $mw -> Frame();
$reset_frm->pack(-fill=>'both');
my $reset_button = $reset_frm->Button(-text=>"Reset",
    -command=> \&do_reset, -font=>"ansi 10 bold")->pack();
MainLoop;
sub print {
    print "$value";
}
sub do_reset {
    $ent->delete(0,'end');
}
sub lam_num_error {
    $mw->messageBox(-message=>"The input must be an integer.");
}