I think that $var eq 'foo' || $var eq 'bar' will work very well. If $var is say 'xyz', the string compare will be abandoned at the first letter. "Oh, its not an 'f', lets see if the first letter is an 'b' ... The regex engine is amazing but an expression like this will just call a low level 'C' function that is very efficient.

My point is that "shorter" source code is not necessary "better" in terms of efficiency or readability.