Single quotes don't allow variable interpolation where as
double quotes do. Here is an example:
#!c:\perl\perl.exe -wT
use strict;
use CGI;
use CGI::Carp qw( fatalsToBrowser );
my $q = new CGI;
my $url = "http://www.perl.org";
print $q->redirect("$url");
print $q->header();