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Buddy Burden
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Debuggit - A fairly simplistic debug statement handler


    use Debuggit DEBUG => 1;

    # say you have a global hashref for your site configuration
    # (not to imply that global vars are good)
    our $Config = get_global_config();

    # now we can set some config things based on whether we're in debug mode or not
    $Config->{'DB'} = DEBUG ? 'dev' : 'prod';

    # maybe we need to pull our local Perl modules from our VC working copy
    push @INC, $Config->{'vcdir/lib'} if DEBUG;

    # basic debugging output
    debuggit("only print this if debugging is on");
    debuggit(3 => "only print this if debugging is level 3 or higher");

    # show off our formatting
    my $var1 = 6;
    my $var2;
    my $var3 = " leading and trailing spaces   ";
    # assuming debugging is enabled ...
    debuggit("var1 is", $var1);   # var1 is 6
    debuggit("var2 is", $var2);   # var2 is <<undef>>
    debuggit("var3 is", $var3);   # var3 is << leading and trailing spaces   >>
    # note that spaces between args, as well as final newlines, are provided automatically

    # use "functions" in the debugging args list
    my $var4 = { complex => 'hash', with => 'lots', of => 'stuff' };
    # this will call Data::Dumper::Dumper() for you
    # (even if you've never loaded Data::Dumper)
    debuggit("var4 is", DUMP => $var4);

    # or maybe you prefer Data::Printer instead?
    use Debuggit DEBUG => 1, DataPrinter => 1;
    debuggit("var4 is", DUMP => $var4);

    # make your own function
    Debuggit::add_func(CONFIG => 1,
            sub { my ($self, $var) = $_; return (lc($self), 'var', $var, 'is', $Config->{$var}) });
    # and use it like so
    debuggit(CONFIG => 'DB');     # config var DB is dev


You want debugging? No, you want sophisticated, full-featured, on-demand debugging, and you don't want to take it out when you release the code because you might need it again later, but you also don't want it to take up any space or cause any slowdown of your production application. Sound impossible? Nah. Just use Debuggit.

Quick Start

To start:

    use strict;
    use warnings;

    use Debuggit;

    my $var = 6;
    debuggit(2 => "var is", $var);      # this does not print
    debuggit(4 => "var is", $var);      # neither does this

Later ...

    use strict;
    use warnings;

    use Debuggit DEBUG => 2;

    my $var = 6;
    debuggit(2 => "var is", $var);      # now this prints
    debuggit(4 => "var is", $var);      # but this still doesn't

That's it. Really. Everything else is just gravy.


This POD explains just the basics of using Debuggit. For full details, see Debuggit::Manual.



DEBUG is a constant integer set to whatever value you choose:

    use Debuggit DEBUG => 2;

or to 0 if you don't choose:

    use Debuggit;

Actually, failure to specify a value only defaults to 0 the first time in a program this is seen. Subsequent times (e.g. in modules included by the main script), DEBUG will be set to the first value passed in. In this way, you can set DEBUG in the main script and have it "fall through" to all included modules. See "The DEBUG Constant" in Debuggit::Manual for full details.

Functions exported

Only "debuggit" is exported.



Use this function to conditionally print debugging output. If the first argument is a positive integer, the output is printed only if DEBUG is set to that number or higher. If the first argument is not a positive integer, the output is printed if DEBUG is non-zero (so omitting the debugging leve is the same as setting it to 1). The remaining arguments are concatenated with spaces, a newline is appended, and the results are printed to STDERR. Some minor formatting is done to help distinguish undef values and values with leading or trailing spaces. To get further details, or to learn how to override any of those things, see "The debuggit function" in Debuggit::Manual.


This is what debuggit is set to initially. You can call it directly if you want to "wrap" debuggit. For examples of this, see "Wrapping the debugging output" in Debuggit::Cookbook.



Add or remove debugging functions. Please see "Debugging Functions" in Debuggit::Manual.


  • Cannot redefine DEBUG; original value of %s is used

    It means you did something like this:

        use Debuggit DEBUG => 2;
        use Debuggit DEBUG => 3;

    only probably not nearly so obvious. Debuggit tries to be very tolerant of multiple imports into the same package, but the DEBUG symbol is a constant function and can't be redefined without engendering severe wonkiness, so Debuggit won't do it. As long as you pass the same value for DEBUG, that's okay. But if the second (or more) value is different from the first, then you will get the original value regardless. At least this way you'll be forewarned.


Debuggit is designed to be left in your code, even when running in production environments. Because of this, it needs to disappear entirely when debugging is turned off. It can achieve this unlikely goal via the use of a compile-time constant. Please see "Performance Considerations" in Debuggit::Manual for full details.


  • Once you set DEBUG, you can't change it. Even if you try, you get the original value. See "DIAGNOSTICS".

  • Doing:

        debuggit(0 => "in production mode");

    never prints anything, even when DEBUG is 0. That's because debuggit is guaranteed to be an empty function when debugging is turned off.

  • Doing:

        debuggit($var, "is the value");

    is inherently dangerous. If $var is a positive integer, debuggit would interpret it as a debug level, and not print it. So, either do this:

        debuggit(1 => $var, "is the value");

    or this:

        debuggit("the value is", $var);

    Or, to look at it another way, you can pass a value as the first arg to print, or you can leave off a debugging level altogether, but don't try to do both at once.

  • Doing:

        my $var1 = "DUMP";
        my $var2 = "stuff";
        debuggit(1 => "vars are", $var1, $var2);

    is equivalent to:

        debuggit(1 => "vars are", DUMP => $var2);

    which is probably not what you wanted, assuming the default functions are still in place. See "IMPORTANT CAVEAT!" in Debuggit::Manual for full details.

  • Doing:

        debuggit(2 => "first thousand elements:", @array[0..999]);

    is likely going to have a performance impact even when debugging is off. Instead, do:

        debuggit("first thousand elements:", @array[0..999]) if DEBUG >= 2;

    See "Style Considerations" in Debuggit::Manual for another example and details on the problem.

That's all I know of. However, lacking omniscience, I welcome bug reports.


Debuggit is on GitHub at barefootcoder/debuggit. Feel free to fork and submit patches. Please note that I develop via TDD (Test-Driven Development), so a patch that includes a failing test is much more likely to get accepted (or at least likely to get accepted more quickly).

If you just want to report a problem or request a feature, that's okay too. You can create an issue on GitHub, or a bug in CPAN's RT (at http://rt.cpan.org). Or just send an email to bug-Debuggit@rt.cpan.org.


    Buddy Burden
    Barefoot Software


This program is free software licensed under

    The Artistic License

The full text of the license can be found in the LICENSE file included with this module.

This module is copyright (c) 2008-2015, Barefoot Software. It has many venerable ancestors (some more direct than others), including but not limited to:

  • Barefoot::debug, (c) 2000-2006 Barefoot Software, 2004-2006 ThinkGeek

  • Barefoot::base, (c) 2001-2006 Barefoot Software

  • Geek::Dev::Debug, (c) 2004 ThinkGeek

  • VCtools::Base, (c) 2004-2008 Barefoot Software, 2004 ThinkGeek

  • Barefoot, (c) 2006-2009 Barefoot Software

  • Company::Debug, (c) 2008 Rent.com


Log::Log4perl, debug, Debug, Debug::Message, Debug::EchoMessage.

Comparison with most of these (and others) can be found in "Comparison Matrix" in Debuggit::Manual.