When you want to match either of two patterns but not capture it, you would use a noncapturing group ?::
/(?:https?|ftp)://(.+)/But what if I want to capture '_1' in the string 'john_1'. It could be '2' or '' followed by anything else. First I tried a non-capturing group:
'john_1'.gsub(/(?:.+)(_.+)/, "")=> ""It does not work. I am telling it to not capture one or more characters but to capture _ and all characters after it.
Instead the following works:
'john_1'.gsub(/(?=.+)(_.+)/, "")=> "john"I used a positive lookahead. The definition I found for positive lookahead was as follows:
q(?=u) matches a q that is followed by a u, without making the u part of the match. The positive lookahead construct is a pair of parentheses, with the opening parenthesis followed by a question mark and an equals sign.
But that definition doesn't really fit my example. What makes the Positive Lookahead work but not the Non-capturing group work in the example I provide?
