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

my $mw = new MainWindow; 

my $ent = $mw -> Entry(
          -bg => 'white',
        ) -> pack();

$ent->focus; # so cursor is there in the entry

$ent->bind('<Return>', \&process_it  );

my $button = $mw->Button(-text => 'Submit',
     -command => \&process_it
  )->pack();

MainLoop;

sub process_it {
 my $var = $ent->get();
 print "$var submitted\n"
}