There are three files in a directory:
ab2 ab23 ab3
When I execute:
ls ab+(2|3)
It displays:
ab2 ab23 ab3
instead of ab2 and ab3 only.
Any ideas why it is like that? Is it a bug?
It's not a bug. +(pattern) matches one or more occurrences of the pattern. +(2|3) will match any combination and any number of 2's and 3's: 2, 3, 23, 32, 222, 333, 3223232323—any of those.
If you want strict alternation without repeats, change + to @:
ab@(2|3)
(Or just use ab[23]. That doesn't even require extglob.)