#!/usr/bin/perl

use strict;
use warnings;


for('hallo K','hallo Karl'){
   if($_ =~ /^(?:\s*\b([a-zA-Z0-9]{2,50})\b\s*)+$/){
     print "$_: yes\n";
   }
   else{
     print "$_: no\n";
   }
}

~ 5> perl community.pl 
hallo K: no
hallo Karl: yes