Validate sprintf format from input field with regex

Question

I have an input field where both regular text and sprintf tags can be entered.

Example: some text here. %1$s done %2$d times

How do I validate the s

Answer 1

The UTF-8 modifier is not necessary unless you use UTF-8 in your pattern. And beside that the sprintf format is more complex, try the following

/%(?:\d+\$)?[dfsu]/

This would match both the %s and %1$s format.

But if you want to check every occurrence of % and whether a valid sprintf() format is following, regular expressions would not be a good choice. A sequential parser would be better.