Filter based on AS-path length

Say you want to only view those bgp prefixes that pass through two or fewer autonomous systems. You can use the following regular expression:
show ip bgp regexp ^[0-9]*_?[0-9]*$

I am sure some guru can write it much more consicely than that. Logically reading left to right it says start at the beginning of the AS path, then accept any set of numerals as an AS, then accept zero or one commas or spaces, then accept any set of numerals as an AS then match with the end of the AS path.