I need a window to update the status of the running processes but my code doesn't work

#!/usr/bin/perl

use Tk;

my $cmd1 = "./test1.sh";
my $msg = "testing";

$main = MainWindow->new();
$main->geometry( '300x100' );

$main->Label( -textvariable => \$msg)->pack( -expand => 1);
$main->Button( -text    => "Run",
               -command => \&test_run)    ->pack(-side => "left");
$main->Button( -text    => "Quit",
               -command => sub { exit } ) ->pack(-side => "right");

MainLoop;

sub test_run {
    my $pid = fork();
    if (not defined $pid) {
       $msg = "resources not avilable.\n";    } else {
    print "I'm the parent\n";
    $msg = "Run $cmd1\n";
    print $msg;

    waitpid($pid, 0);
    my $ret = $? >> 8;
    $msg = "$cmd1 exit with return value $ret\n";
    }
 
    #more forked child...

}
[download]

The label widget didn't get updated.

Thanks!