How to Use a Query String in Perl

A query string is the part of a URL which is attached to the end, after the file name. It begins with a question mark and usually includes information in pairs. The format is parameter=value, as in the following example:

www.mediacollege.com/cgi-bin/myscript.cgi?topic=intro

Query strings can contain multiple sets of parameters, separated by an ampersand (&) like so:

www.mediacollege.com/cgi-bin/myscript.cgi?topic=intro&heading=1

The idea is that the information contained in the query string can be accessed and interpreted by a script. Specifically, the query string data is contained in the variable $ENV{'QUERY_STRING'}.

To Access the Query String Data

You can use a block of code like the one below to access and organise the query string:

if (length ($ENV{'QUERY_STRING'}) > 0){
      $buffer = $ENV{'QUERY_STRING'};
      @pairs = split(/&/, $buffer);
      foreach $pair (@pairs){
           ($name, $value) = split(/=/, $pair);
           $value =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack("C", hex($1))/eg;
           $in{$name} = $value; 
      }
 }

This code will create a hash called $in, from which you can call specific variables like so:

$topic = $in{'topic'};
$heading = $in{'heading'};