Devel::XRay - See What a Perl Module Is Doing


Version 0.95


use Devel::XRay along with ignore, only, or all,

    use Devel::XRay;
    use Devel::XRay 'all';    # same as saying 'use Devel::XRay;'
    use Devel::XRay 'none';   # filter the source but don't inject anything
    use Devel::XRay ignore => qw(man_behind_curtain private);
    use Devel::XRay only   => qw(sex drugs rock_and_roll);


Devel::XRay is a handy source filter using Filter::Simple when used at the top of perl code, will inject print statements to standard error to show you what a module is doing.

This module is useful if...

  • You're a visual learner and want to "see" program execution

  • You're tracking an anomaly that leads you into unfamiliar code

  • You want to quickly see how a module _runs_

  • You've inherited code and need to grok it

  • You start a new job and want to get a fast track on how things work


    use strict;
    use warnings;
    use Devel::XRay;

    use Example::Object;

    my $example = Example::Object->new();
    my $name = $example->name();
    my $result = $example->calc();

    sub init    {}
    sub cleanup {}

    # In a another file, say Example/
    package Example::Object;
    use Devel::XRay;
    sub new { bless {}, shift }
    sub name {}
    sub calc {}

Produces the following output

    # Hires seconds     # package::sub
    [1092265261.834574] main::init
    [1092265261.836732] Example::Object::new
    [1092265261.837563] Example::Object::name
    [1092265261.838245] Example::Object::calc
    [1092265261.839443] main::cleanup


This module was inspired by Damian Conway's Sufficently Advanced Technology presentation at YAPC::NA 2004. I had initially attempted to use Hook::LexWrap, but using Filter::Simple was just a lot cleaner and seemed a bit more practical for debugging code. The first iteration was only 2 lines of actual code.

    package Devel::XRay;
    use strict;
    use warnings;
    use Filter::Simple;

    my $code = 'print STDERR (caller(0))[3] . "\n";';
    FILTER { return unless $_; $_ =~ s/(sub.+?{)/$1 $code/sg; }

I'd also like to thank fellow member Rocco Caputo for working out the import logic over Sub Etha Edit at OSCON. Rock on Rocco!


Jeff Bisbee, <jbisbee at>


Please report any bugs or feature requests to bug-devel-xray at, or through the web interface at I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.


You can find documentation for this module with the perldoc command.

    perldoc Devel::XRay

You can also look for information at:


Copyright 2006 Jeff Bisbee, all rights reserved.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.


JavaScript::XRay, Filter::Simple, Time::HiRes, Hook::LexWrap, Devel::Trace