Something like this (untested and I am rusty): 
eval {require Text::LevenshteinXS};
if ($@) {
  eval {require Text::Levenshtein};
  else {
    require "Levenshtein.lib";
  }
}

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In reply to Re: how to determine whether a module is installed or not? by tilly
in thread how to determine whether a module is installed or not? by Anonymous Monk

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