C# Regular expression combination

Question

I just wondered if I can combine these two expressions into one.

 Regex comb1 = new Regex("[A-Z0-9]{4,6}-[A-Z0-9]{4,6}-[A-Z0-9]{4,6}");
 Regex comb2 = new Regex("[A-Z0-9]{4,6}-[A-Z0-9]{4,6}-[A-Z0-9]{4,6}-[A-Z0-9]{4,6}");

Answer 1

In general you would use alternations ( | ) to match one of a several patterns. For example:

aaa|bbb

Will first attempt to match the pattern aaa and then attempt to pattern bbb .

However, because your patterns are so similar, you could just use something like this:

[A-Z0-9]{4,6}(-[A-Z0-9]{4,6}){2,3}

This will match any sequence of four to six alphanumeric characters, followed by a hyphen and four to six alphanumeric characters, which must be repeated two or three times.

Answer 2

If you have an optional part in a pattern, you can use (OptionalPattern)? , so your code could become:

[A-Z0-9]{4,6}-[A-Z0-9]{4,6}-[A-Z0-9]{4,6}(-[A-Z0-9]{4,6})?

But pswg's {2,3} is a better choice here, since it also eliminates the unnecessary repetition in your pattern. I'm just mentioning since it can be useful in similar situations.