First question: what do you mean by "it broke"? Does it give an error message, or just give incorrect behaviour?

By default, perl will include a filename and line number on fatal errors unless they terminate in a newline. You can also modify the script to make a fatal error give a full stack trace in most cases, by adding something like this just after the shebang line:

BEGIN { use Carp; $SIG{__DIE__} = sub { Carp::confess(@_) } }
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If the script is completing without a fatal error, but giving incorrect behaviour, you can insert this just after the shebang line to get a list of the paths to all modules that were loaded up to the point the script finishes:

END { print for values %INC }
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