Using regex to match string between two strings

Question

How can I use a regular expression to match text that is between two strings, where those two strings are themselves enclosed two other strings, with any amount of text between the inner and outer enclosing strings?

For example, I have this text:

outer-start some text inner-start text-that-i-want inner-end some more text outer-end

In this case, I want text-that-i-want because it is between inner-start and inner-end, which themselves are between outer-start and outer-end.

If I have

some text inner-start text-that-i-want inner-end some more text outer-end

then I don't want text-that-i-want, because although it is between inner-start and inner-end, there is no outer-start enclosing these strings.

Likewise, if I have

outer-start some text text-that-i-want inner-end some more text outer-end

then again, I don't want text-that-i-want, because there is no enclosing inner-start, although there are enclosing outer-start and outer-end strings.

Assume that outer-start, inner-start, inner-end and outer-end will only ever be used for the purposes of enclosing/delimiting.

I reckon that I can do this by doing a two pass regular expression match, i.e. looking for any data between outer-start and outer-end, and then within that data looking for any text between inner-start and inner-end (if indeed those strings exist), but I would like to know if it can be done in one go.

Answer 1

I imagine you can do something like:

outer-start .*? inner-start (.*?) inner-end .*? outer-end

Answer 2

/outer-start.*?inner-start(.*?)inner-end.*?outer-end/

You need to use minimal matching to keep the regexp engine from malfunctioning when there are multiple "texts-that-i-want"s, for example:

"outer-start some text inner-start first-text-that-i-want inner-end some more text outer-end outer-start some text inner-start second-text-that-i-want inner-end some more text outer-end"

Without minimal matching, you'll get the puzzling single match, "second-text-that-i-want".

The .*? means "eat zero or more characters, but only as many as you need to to make the rest of the expression match. With the ?, a regexp engine will eat as many characters as it can as long as the rest of the expression matches.