#!/usr/bin/perl
use strict;
use warnings;
use CGI::Simple;

my $baseurl = 'http://www.example.com/helps';
my %available_topics = (
  home => 'home.html',
  user => 'user.html',
  add => 'add.html',
  update => 'update.html',
  remove => 'remove.html',
  #... other help topics
);
my $default_topic = 'home';

my $cgi = CGI::Simple->new; # let CGI::Simple does the parsing
my $topic = $cgi->param('topic') || ''; # get the wanted topic
# get corresponding html file
my $help_file = $available_topcs{$topic} || $available_topics{$default_topic};

# send redirection
print $cgi->redirect("$baseurl/$help_file");