I need to include a certain restriction in the username validation.

A username can only contain the following characters in its name:

• a-z
• A-Z
• 0-9
• ._-

In addition, I want to display failed matches in the view so that the user can change his input.

Thus, the usual regex would be: @"^[a-z0-9._-]$"(ignoreCase).

But this pattern can’t tell me exactly which match was unsuccessful.
To satisfy my additional requirement, I have to do the following:

@"^(?:(?<letter>[a-z])|(?<numeric>[0-9])|(?<character>[._-]))*$".

But this will work if the match is successful. If the match fails, I can’t get which group didn’t work.
So I have to invert the pattern and match successful when input is wrong. And here I can’t understand how to properly use negate in order to get right pattern…

I figure that if I invert the regex match, I can figure out which character the user entered incorrectly and output a list of the rules they violated

For example:

• only [a-z]
• only . _ –

If the user entered : someNonLatinWord

Is there a better approach?