How to match end of string in lookahead?

Question

Why this do not match and how to make it work?

Regex.Match("qwe", ".*?(?=([ $]))");

I should match everything to first space or to the end of line.

Answer 1

Your specific problem is that you need to use an alternation, not a character class, because inside a character class the $ symbol literally means "match a dollar symbol", and does not have its special meaning end-of-line in that context.

( |$)

It seems however that your example is a bit strange. It would be simpler to match any character except space, then you wouldn't need a lookahead at all.

Answer 2

Try with:

Regex.Match("qwe", "^([^ ]*)");