#!/usr/bin/perl -wT
#warnings and Taint checking on, see perlsec 

#CGI scripts should almost always use CGI.pm
use CGI;
use strict;  #strict is your friend

my $q = new CGI;
print $q->header();  #print the header

my $comment = "My lawyer is named will";

#this loops over the list in the parens, aliasing $new to each in turn
#pointless, but presumably you anticipate having more than one in the list
for my $new ($comment) {
  $new = doit($new);  #We act on $new, which will affect whichever list element we're on
}
print $comment;  #$comment, not $new.  $new was only inside the loop


sub doit{
  my ($passed_string) =  @_;  #get the list we're passed, drop all but first item
  #Note that I removed the "e" flags below, you aren't interpreting anything
  my $go = ";gi/moT/lliw/s ;gi/reknaB/reywal/s ;gi/yenraB/derf/s";
  my $com = scalar reverse $go;
  $_ = $passed_string;  #so that s// will work on it.
  eval $com or die $!;
  return $_;
}