I have String that can be for example 3D-F2-C9-A6-B3
This is my regex and I've validated it by an online regex tester:
^([0-9A-Fa-f]{2}[-]){0,}$
The problem is, that the example string 3D-F2-C9-A6-B3-4F is not valid. I have to add a minus at the end like 3D-F2-C9-A6-B3-4F-
How can I change the regex that the separators in the middle have to be set but no one at the end?
The best way is to unroll it a bit:
^[0-9A-Fa-f]{2}(?:-[0-9A-Fa-f]{2})*$
See the regex demo
Details:
^ - start of string[0-9A-Fa-f]{2} - 2 chars from the defined set(?:-[0-9A-Fa-f]{2})* - zero or more sequences of
- - a literal hyphen[0-9A-Fa-f]{2} - 2 chars from the defined set$ - end of string (better option is \z to match the very end of the string)var pattern = @"^[0-9A-Fa-f]{2}(?:-[0-9A-Fa-f]{2})*\z";
var input = "3D-F2-C9-A6-B3";
var matched = Regex.IsMatch(input, pattern); // = > True
^([0-9A-Fa-f]{2}[-]?){0,}$ (note a ? in [-]?). This way, matching is becoming non-linear, it also allows - to appear at the end of the string, and in some cases leads to poorer performance with very long strings. Repeating the pattern like yours ([0-9A-Fa-f]) is not a big problem here (you can even shorten it using RegexOptions.IgnoreCase and removing A-Z), else just build the pattern dynamically by defining a variable with the repeated block.