Question

I can split a string into two based on 2 spaces:

string Line = "1  2";

Regex.Split(Line, "  ");

=> 1, 2

I would like to add an exception. Only split if ‘not enclosed by [ ]’ as shown in this example.

string Line = "1  2  [1  2]";

Regex.Split(Line, "  ");

=> 1, 2, [1 2]

Can I fairly easily achieve this via regex? By the way, I use .NET.

Answer 1

You could use a lookahead, that asserts that there is no closing ] before the next opening [ or the end of the string:

Regex.Split(Line, @"[ ]+(?![^\[\]]*\])");

This will fail you if you have nested [...] structures though. Note that the lookahead is not part of the actual match, it just checks what follows without consuming anything. Inside the lookahead I used [^\[\]] which is a negated character class, matching any character except for any kind of square bracket.

Also note that this splits on 1 or more spaces. If you want to require at least two, replace [ ]+ with [ ]{2,} and if you want exactly two with [ ]{2}.

Further reading on lookarounds.