Why doesn't this Regex work in .NET?

Question

I want a regex that will verify that a string begins with a letter followed by some letters, numbers, or underscores. According to my EditPadPro regex parser the following test should pass. But it does not.

Regex.IsMatch("Class1_1", @"^\w[\w|\d|_]*$").ShouldBeTrue();

What am I missing?

Answer 1

Your regex works, but doesn't do what you think it does.

You should use

Regex.IsMatch("Class1_1", @"^[A-Za-z]\w*$")

(Tested)

Answer 2

\w includes \d and underscore - even if your test passes, the Regex won't be testing what you want it to!