Because there’s non-programmers in this community, if you aren’t sure what this means but are too afraid to ask, it’s a Regular Expression that better represents the terms “Linux” and “Unix.”
Though if we’re going to be that pedantic, it would be
[nN][uiI][xX]$
. That extra pipe wouldn’t actually do anything in the last example, because regexp picks one character from the set by default.And if we want to be really pedantic,
(?!nix)[nN][uI][xX]$
Would be the most accurate.
We’re talking about Unix so being as pedantic as possible is actually required.
Isn’t
(I|U)
equivalent to([IU])
?Yes, but you can really only do that with single characters, since your first example is an ordered group and the second is an unordered set in a capturing group. The equivalency drops off when you include more characters.
Plus, you can do things like
[
, and you can’t do that with the former example. ]I would imagine there’s a difference in computing overhead, too, but I have no idea which is more performant.