Regex with all optional parts but at least one required

Question

I need to write a regex that matches strings like \"abc\", \"ab\", \"ac\", \"bc\", \"a\", \"b\", \"c\". Order is important and it shouldn\'t match multiple appearances of th

Answer 1

To do this with pure regex you're going to have to expand it into all of its possibilities:

ab?c?|a?bc?|a?b?c

If you have lookaheads you can make sure the string is non-empty. Or you can verify the string has a length of at least one before passing it to the expression, depending on your choice of language.

For example a .NET lookahead might look like this:

^(?=[abc])a?b?c?$

Or you could just test your string's length before matching it:

if (YourString.Length == 1) {
   // matching code goes here, using the expression a?b?c?
}