Suppose I have the set of characters [ABC]. I'm looking for a regex that would match any permutation of the superset except the empty set, i.e.
ABC ACB BAC BCA CAB CBA
AB BC AC CB CA BA
A B C
The regex should (obviously) not match the empty string.
p.s. An alternative way to express the same objective is "match any non-empty string containing each character in the set at most once".
update: The set [ABC] is just an example, for the real set may also be bigger. With this question I was hoping to find a "general" solution rather than a particular one for [ABC].
Thanks to your answers (especially anubhava's and codaddict's) I was able to find this solution, that I think is pretty elegant because it allows to type the set only once:
\b(([ABC])(?!.*\2))+\b
the \b are needed to match full words; omitting them will also find subwords respecting the required property. To match a full string, you'd obviously do:
^(([ABC])(?!.*\2))+$