my $fractionValue =
    ( $str =~ m{^(\d+)/([1-9]\d*)} )   # regex match will evaluate to true or false
    ?            # the "ternary operator" -- if above condition is true, then...
    $1/$2        #   return this value (using the 1st and 2nd matched digit strings
    :            # otherwise (if above condition was false), ...
    "undefined"  #   return this value
    ;            # end of statement