#!/usr/bin/perl use warnings; use strict; use Tk; use utf8; my($Test, $Laenge, $Meldung) = ""; my $mw = MainWindow->new(); my $ent = $mw->Entry(-validate => 'key', -validatecommand => \&check, -foreground => "black", -background => "white"); $ent->focus(); $ent->pack(-side=>'top', -padx => 20, -pady => 20); MainLoop(); sub check { my $Test = $ent->get(); if(length($Test)>1) { $ent->configure(-foreground => 'red'); } else { $ent->configure(-foreground => 'black'); } return 1; }