#!/usr/local/bin/perl -wT
use strict;
use CGI;
...
 $username =~ s/\W//g;
    if ($username =~ /(\w{2,16})/)
      {
        $username =~ $1;
        $username =~ tr/[A-Z]/[a-z]/;
      }
 else
      {
        #since username isnt able to be safe, it is empty
        $username ="";
      }

`/bin/echo $username`;