If you use diagnostics perl will tell you which category the warning belongs to. For example, printing an uninitialised variable yields (the category is in bold):
Use of uninitialized value $x in print at
/home/bri/foo.pl line 14 (#1)
(W uninitialized) An undefined value was used as if it were already
defined. It was interpreted as a "" or a 0, but maybe it was a mistake.
To suppress this warning assign a defined value to your variables.
Additionally, perldiag lists all of perl's warning and error messages.

Perl: perlintro    perlretut    perldoc    Basic debugging checklist    Yes, even you can use CPAN
PerlMonks: How do I post a question effectively?    Markup in the Monastery    How do I post a question effectively?    I know what I mean. Why don't you?
General: How To Ask Questions The Smart Way    What every computer scientist should know about floating-point arithmetic
To Be Continued...

In reply to Re^3: Annoying 'Use of uninitialized value in concatenation' warning by FunkyMonk
in thread Annoying 'Use of uninitialized value in concatenation' warning by alain_desilets

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