I also like using Data::Dumper when debugging my CGI scripts.

#!/usr/bin/perl -T
use strict;
use warnings;
use CGI qw(:standard);
use CGI::Carp qw(fatalsToBrowser);
use Data::Dumper;
print "Content-type: text/plain\n\n";
my $color=param('color');
print Dumper($color);
exit;
print "Your chosen color is $color.\n";
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# ./color.cgi color=red
Content-type: text/plain

$VAR1 = 'red';
[download]

It's useful when the script is big and all you want is to check a variable in a middle of it.