alternative greedy match

I want to make a greedy match to开发者_运维知识库 an alternative of either zero to 'm' consecutive occurences of 'a' or zero to 'n' consecutive occurences of 'b'. If I do

/a{,m}|b{,n}/

it will not work because when I have sequences of 'b', it will match with 'a{,m}', and the alternative 'b{,n}' will not be looked at, and it will not be a greedy match.

If I understand what you're trying to do correctly, how about /(?:a{1,m}|b{1,n})?/

It'll match either a string of consecutive a's (up to m times), or a string of consecutive b's (up to n times), or nothing at all due to the optional ?.

I think by default, quantifiers are greedy and from left to right. So its not really a greedy issue you were having its the a{0,m} in the alternation matching in the presence of non a's. It would have matched up to 'm' a's had they been present first.

Greediness seem's more complicated than someone might guess.

'aaaaaaaaaa' =~ /(a{1,2}) (a{1,2}?) (a{1,4}) (a{4,12}+)/x &&
print "'$1', '$2', '$3', '$4'";

'aa', 'a', 'aaa', 'aaaa'