The "use of uninitialized value" error arise when you use a variable that hasn't been defined before.

As for debugging your code, make sure you put

use warnings;
use strict;
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at the beginning of your script. Also, when asking for help make sure you reduce your code to a minimum (try to post only the part of the code causing the errors), and giving the exact errors messages would help too.

Other than that, to debug you could add more "or die" statements and sprinkle your code with "print" statements outputting the value of your variables to make sure they contains what you think they contains.

Guillaume