Dealing with multiple (optional) tokens)

[kootenpv]

How do you recommend dealing with multiple (optional) tokens?

Let's say we want to extract abc or a subset of it; the regex would be:

(a)?(b)?(c)?

This will allow matching all combinations:

abc
ab
ac
bc
b
c
a

Is the best we can do having to add all combinations, including "" and then joining them?