#!/usr/bin/perl -w
use HTTP::Proxy;
use HTTP::Proxy::BodyFilter::simple;
use HTTP::Proxy::BodyFilter::complete;

my $proxy = HTTP::Proxy->new;
# pass the complete response body to our filter (in one pass)
$proxy->push_filter(
    mime => 'text/html',
    response => HTTP::Proxy::BodyFilter::complete->new,
    response => HTTP::Proxy::BodyFilter::simple->new(
        sub {
            my ( $self, $dataref, $message, $protocol, $buffer ) = @_;
            $dataref =~ s/Perl/PERL/;
        }
    )
);
$proxy->start;