Whatch out for:

  if ($variable and $variable eq 'value') {
    # do something
    # ...
  }
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as you are testing not only that the value is defined, but that the value is also not zero or an empty string. As a general practice, you should be writing:

  if ((defined $variable) && ($variable eq 'value')) {
    # do something
    # ...
  }
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