If you've ever used eval, or any modules, chances are you've had an error like this: 
Use of uninitialized value in string eq at (eval 469) line 3.

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It's telling you that somewhere on the 3rd line of the code passed to the 469th call to eval, you're using an undefined value. That's not very fun! Who knows where eval was called the 469th time? You could walk through your program and try to keep track of every time eval was called, but that's not very fun. So what to do?

Turn your warning handler into something more descriptive. At the top of your code, do this: 

use Carp;
$SIG{__WARN__} = \&carp;
$SIG{__DIE__} = \&confess;

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carp and confess are equivalent to warn and die, respectively, except that they print a stack trace as well as the error message. Now, rerun your code and get 
Use of uninitialized value in string eq at (eval 469) line 3.
at /home/alester/Lib/TW/CP.pm line 116

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No counting of eval calls required!

In reply to HOWTO: Finding errors "at (eval 469) line 3" by petdance

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