My money's on the config file. Perhaps a permissions problem?

If so, the script could probably benefit from better error detection. If an IP address is required (as it seems to be) the code should validate that it has an IP address early on, and give a more informative error message.

Some tools for chasing down the problem:

• use 'strace' to see what the script does when it runs. If it fails to open() a config file, you'll see an error code (e.g. EPERM) which tells you why. The output of strace is voluminous, but you can send it to a file and grep it.
• add some debugging to your script. log the value of the ip address at different stages of the processing.
• make sure your script is handling errors correctly (a good way is to just 'die' if an unrecoverable problem occurs. e.g:

  my $cfg_file = "/my/config/file";
  open(my $fh, "<", $cfg_file)
      or die "can't read config file [$cfg_file] for reading: $!";
  [download]

  Note that we putting $! in your error handling gives you the reason why the open failed, which may help you track down the problem.

As others have noted, I'm speculating wildly because we can't see your code. On the other hand, if your script is large it may not be useful to see all of it.

If you can try reducing your script to the minimum amount which reproduces the problem that would be useful. You'll also often find that doing that helps you find the problem yourself.

Good luck.