Using regex to match string between two strings while excluding strings

Question

Following on from a previous question in which I asked:

How can I use a regular expression to match text that is between two strings, where those two

Answer 1

You can't easily do that with plain regexes, but some systems such as Perl have extensions that make it easier. One way is to use a negative look-ahead assertion:

/outer-start(?:u(?!nwanted)|[^u])*?inner-start(.*?)inner-end.*?outer-end/

The key is to split up the "unwanted" into ("u" not followed by "nwanted") or (not "u"). That allows the pattern to advance, but will still find and reject all "unwanted" strings.

People may start hating your code if you do much of this though. ;)