Regex - Match any character except character

Question

My goal is to match each group starting with __ and ending with __.

For example, in this text:

__1__
__2____3__
__4_4__

We can find 4 groups.

With this regex

__.[^__]*__ 

the last group doesn't match.

With this one

__(?!(^_)$).*__ 

the 2nd and 3rd groups are gathered in one.

What is the solution please?

Answer 1

You can use

__.+?__

You might be surprised that I didn't say anything about "don't match any underscores along the way", since in all your attempts you tried to something like that.

The trick is to use +? , a lazy quantifier. I allow the regex to match any character ( . ), but as few times as possible , such that there are two underscores after it. It's as if after matching each character, the regex engine always asks "are there two underscores ahead?". And if there are, that's where the quantifier stops matching.

See this for more info about lazy vs greedy quantifiers.