in reply to trap run time errors

Just one easy but useful command to find the reason why you obtained an uninitialized value warning when processing, say, line 1,234,687 of your input.txt file:

$ perl -ne 'print if $. == 1234687' input.txt

Or, if your file is much longer than 1,234,687 lines:

$ perl -ne 'print and exit if $. == 1234687' input.txt

In Section Seekers of Perl Wisdom