How to write an expression where (the last comma is optional)?

Question

Regular Expressions

I want to check input tags. Tags consist of letters and numbers, separated by commas, there can be any number of spaces between tags.
The following expression almost copes: [ ]*([a-zA-Z0-9]+,[ ]*)*the only annoying thing is that you need to put a comma after the last tag. How can I make the last comma optional?

Answer 1

preg_match('/^ *[a-z\d]+(, *[a-z\d]+)*,? *$/i', $text);