On 12/29/21 08:31, Davide Brini wrote:
> I think you need to use '+' before the offending token

Yes. That's a GNU extension. If you want to be portable to any POSIX
implementation, you can use this instead:

expr "X(" : '.*' - 1

A similar example is given in the POSIX spec for 'expr':

https://pubs.opengroup.org/onlinepubs/9699919799/utilities/expr.html

As this is not a bug, I'm closing the bug report.