As the only -- of note is in a regular expression and |is a magic character in regular expressions, if you replaced the -- with a | the regex becomes quite a different animal. You should read perlretut for an introduction to regular expressions.

You may get more help from us if you show us the version of the code that generates errors and tell us what you consider the errors to be. Showing us a sample of the output you get and what you expected to see may help too.