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

use constant MAXBYTES => 5;

$| = 1;

MSG: print "Please be aware maximum length ${\MAXBYTES} characters!:\n";

my $result;
do {
    print "Send this text to clients:\n\n";
    chomp ($result = <STDIN>);
    if (length($result) >= MAXBYTES) {
        print "\nYou have reached the limit of characters ",
              length $result,
              "!\n\n";
        goto MSG
    }
} until uc $result eq "END";