I want to match an optional tag at the end of a line of text.
Example input text:
The quick brown fox jumps over the lazy dog {tag}
I want to match the part in curly-braces and create a back-reference to it.
My regex looks like this:
^.*(\{\w+\})?
(somewhat simplified, I'm also matching parts before the tag):
It matches the lines ok (with and without the tag) but doesn't create a back-reference to the tag.
If I remove the '?' character, so regex is:
^.*(\{\w+\})
It creates a back-reference to the tag but then doesn't match lines without the tag.
I understood from http://www.regular-expressions.info/refadv.html that the optional operator wouldn't affect the backreference:
Round brackets group the regex between them. They capture the text matched by the regex inside them that can be reused in a backreference, and they allow you to apply regex operators to the entire grouped regex.
but must've misunderstood something.
How do I make the tag part optional and create a back-reference when it exists?
It is not a backreference problem, the problem is that the regular expression was satisfied by just reading in the text that matched .*. It didn't feel compelled to continue reading to read the optional end-tag. The simplest solution if you're truly reading to the end of the line is to append a $ (dollar sign) to force the regular expression to match the whole line.
edit
BTW, I didn't take your reg-ex literally since you said it matches other stuff, but just to be clear .* will consume the whole line. You'd need something like [^{]* to prevent the tag from getting swallowed. I'm guessing that's not a problem for you.