Error and warning messages are listed in perldiag. Each has a more verbose description: such as that shown by ++choroba in the first response you received.

As a debugging aid, you can use the diagnostics pragma. [Note: this also documents "The splain Program".] Use something like this near the top of your script:

use strict;
use warnings;
use diagnostics;
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This pragma is a developer tool. Its output, which can be quite lengthy, is generally not suitable for end-users (too long, too technical, etc.) and it can swamp log files (messages you really want to see can become lost amongst all this verbiage).

My general advice is:

• Only use this pragma while you are learning and having difficulty understanding the terse, one-line messages.
• Remove the 'use diagnostics;' line from production code.