I'm mildly suprised that no-one caught the problem in the following line:
  $process = qr/\s+(?:\d+[:])+?\d+\s+.*?$ARGV[0].*?\s*$/;

Because I'm using user input in a regexp, I should have done one of the following:

  # use \Q and \E
  $process = qr/\s+(?:\d+[:])+?\d+\s+.*?\Q$ARGV[0]\E.*?\s*$/;
  # or enclose in an eval
  eval { $process = qr/\s+(?:\d+[:])+?\d+\s+.*?$ARGV[0].*?\s*$/; };
  if($@) { ... }
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I chose to go with the eval { ... } version mainly because I actually want regexp functionality on the command line.