Dump the content of an arbitrary Perl data structure

Objective

To dump the content of an arbitrary Perl data structure to STDERR.

Scenario

Suppose that you are attempting to troubleshoot a Perl script and need to inspect the content of a data structure referenced by the variable $data. You know what the layout of this data structure should be, however there is a significant possibility that it has not been constructed as intended.

Method

You can dump the content of a Perl data structure using the Data::Dump module. First the module must be installed. On Debian-based systems it is located in the package libdata-dump-perl:

apt-get install libdata-dump-perl

The next step is to load the module. The specific function that you need to import is called dump:

use Data::Dump qw(dump);

You should now be able to inspect any data structure by passing it to dump:

my $data = {username=>'user',password=>'xyzzy'};
dump $data;

If dump is evaluated in a void context then the output will be sent to STDERR. In this particular example it should look similar to:

{ password => "xyzzy", username => "user" }

This is an executable fragment of Perl code which, if evaluated using eval, would reconstruct a copy of the original data structure.

Variations

Dump to a location other than STDERR

When evaluated in a non-void context dump returns its output as a string instead of writing it to STDERR. You can then use it in whatever manner is appropriate, for by example sending it to syslog:

use Data::Dump qw(dump);
use Sys::Syslog;

my $data = {username=>'user',password=>'xyzzy'};

openlog($0,'',LOG_USER);
syslog(LOG_DEBUG,dump($data));
closelog;

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