Question

I am using Regex.IsMatch() to evaluate a list of words.

The Regex should return true if the following strings are evaluated:
-hellotest
-helloabc
-abchello

and the Regex should return false if the following strings are evaluated:
-helloworld
-worldtest
-abcworld

Basically I want it to return true if the word "hello" is found in the string and if the word "world" is not found in the string.

What’s the Regex to produce such result?

Answer 1

Use the expression

(?<!world.*)hello(?!.*world)

---

(?<!prefix)pos is a negative lookaround. pos is only matched, if it is not preceeeded by prefix

pos(?!suffix) is only matched if it is not succeeded by suffix