use strict;
use warnings;
use constant MAXBYTES => scalar 5;

my $result;

$| = 1;
MSG: 
    print "Please be aware maximum length 255 characters!:\n"; 
    
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($result)."!\n\n";
    goto MSG;
    }
} until ($result eq "END" or $result eq "end");
$| = 1;