First of all, creating variables like that is quite dangerous. You could quite easily find yourself setting a value that might overwrite something in your program. Having a hash that has the variable name as it's key, and the variable's value as it's value is much safer.

Second, the /%(.*)\s*=\s*(.*)/ regexp is not exactly the same as the other one: the .* is greedy, therefore it will consume all the blanks before the equals sign. Your $1 will have trailing blanks if there are any trailing blanks to be had.(And what is the % doing there?)

Third, you do know that the $options as you posted it here will not match MN, don't you>? This is because it doesn't contain the letter M or N, and because it only accepts one letter, you need a + or a count like {n,m} to match it correctly.