Regex to match a hyphen in a string 0 or 1 times

Question

I am trying to build a regex that will check to see if a string has a hyphen 0 or 1 times.

So it would return the following strings as ok.

1-5
1,3-5
1,3

The following would be wrong.

1-3-5

I have tried the following, but it is fine with 1-3-5:

([^-]?-){0,1}[^-]

Answer 1

This works:

^[^-]*-?[^-]*$
^^    ^ ^    ^
||    | |    |
||    | |    |-- Match the end of string
||    | |------- Match zero or more non-hyphen characters
||    |--------- Match zero or one hyphens
||-------------- Match zero or more non-hyphen characters
|--------------- Match the beginning of string

In this case, you need to specify matching the beginning (^) and end ($) of the input strings, so that you don't get multiple matches for a string like 1-3-5.

Answer 2

Perhaps something simpler:

var hyphens = input.Count(cc => cc == '-');

Your regular expression works because it found the first instance of a hyphen, which meets your criteria. You could use the following regular expression, but it would not be ideal:

^[^-]*-?[^-]*$

Answer 3

If you have your strings in a collection, you could do this in one line of LINQ. It'll return a list of strings that have less than two hyphens in them.

var okStrings = allStrings.Where(s => s.Count(h => h == '-') < 2).ToList();

Judging by the way you've formatted the list of strings I assume you can't split on the comma because it's not a consistent delimiter. If you can then you can just using the String.Split method to get each string and replace the allStrings variable above with that array.