Perl Language Debug Output Dumping with Style


Sometimes Data::Dumper is not enough. Got a Moose object you want to inspect? Huge numbers of the same structure? Want stuff sorted? Colored? Data::Printer is your friend.

use Data::Printer;

p $data_structure;

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Data::Printer writes to STDERR, like warn. That makes it easier to find the output. By default, it sorts hash keys and looks at objects.

use Data::Printer;
use LWP::UserAgent;

my $ua = LWP::UserAgent->new;
p $ua;

It will look at all the methods of the object, and also list the internals.

LWP::UserAgent  {
    Parents       LWP::MemberMixin
    public methods (45) : add_handler, agent, clone, conn_cache, cookie_jar, credentials, default_header, default_headers, delete, env_proxy, from, get, get_basic_credentials, get_my_handler, handlers, head, is_online, is_protocol_supported, local_address, max_redirect, max_size, mirror, new, no_proxy, parse_head, post, prepare_request, progress, protocols_allowed, protocols_forbidden, proxy, put, redirect_ok, remove_handler, request, requests_redirectable, run_handlers, send_request, set_my_handler, show_progress, simple_request, ssl_opts, timeout, use_alarm, use_eval
    private methods (4) : _agent, _need_proxy, _new_response, _process_colonic_headers
    internals: {
        def_headers             HTTP::Headers,
        handlers                {
            response_header   HTTP::Config
        local_address           undef,
        max_redirect            7,
        max_size                undef,
        no_proxy                [],
        protocols_allowed       undef,
        protocols_forbidden     undef,
        proxy                   {},
        requests_redirectable   [
            [0] "GET",
            [1] "HEAD"
        show_progress           undef,
        ssl_opts                {
            verify_hostname   1
        timeout                 180,
        use_eval                1

You can configure it further, so it serializes certain objects in a certain way, or to include objects up to an arbitrary depth. The full configuration is available in the documentation.

Unfortunately Data::Printer does not ship with Perl, so you need to install it from CPAN or through your package management system.