Stop At The First One

Capture everything before the FIRST equals sign: key=value=other gives key.

.* is greedy — it takes the whole string and hands characters back only as far as it must, so (.*)= lands on the LAST equals sign and gives you key=value. Two fixes, both worth knowing: make the quantifier lazy with (.*?)=, or say what you actually mean with a negated class, ([^=]+)=, which cannot cross an equals sign in the first place. The second is usually both shorter and faster. A string with no equals sign at all must not match.