如何强制正则表达式匹配模式的最长部分。

Question

I have a pattern in .net and I want a string be matched with longest possible part of the pattern

Pattern : "I (?<a>[\w\W]*)(want to match (?<b>longest))? available"
or "I ((?<a>[\w\W]*)|(want to match (?<b>longest))?)+ available"

String :

after match we have :
but i want :

Answer 1

RegEx is "greedy" by default, meaning it will match as much as possible . To make a repetition lazy , add a ? .

I <?a:[\w\W]*?>(want to match <?b:longest>)? available
             ^

This will now match 0+ [\\w\\W] characters lazily, or in other words: until the expression can continue to match (once it sees want to match longest available , etc).

Examples: greedy vs. lazy (click 'regex debugger' to see how each of these repetitions operates).

Same idea goes with your other expression, however the greediness is a problem in a different location:

I ((?<a>[\w\W]*)|(want to match (?<b>longest))?)+? available
                                                 ^