bug#79410: Error in expr match handling patterns with null expression subpatterns

On 2025-09-08 10:05, Michael Figiel via GNU coreutils Bug Reports wrote:
> The expected behaviour is on FreeBSD and OpenBSD, so different code
> base, but I think it's more consistent with the POSIX description of
> expr.

My reading of POSIX is that the GNU behavior is required and the FreeBSD 
behavior is correct. Admittedly this is an obscure corner of the spec.

For what it's worth, GNU sed (and I assume other GNU programs) agree 
with GNU expr and with traditional (e.g., Solaris) expr:

$ echo /usr/local/lib/erlang28/bin:/sbin:/bin:/usr/sbin:/usr/bin | sed 
's|\(.*:\)\{0,1\}/usr/local/lib/erlang28/bin\(:.*\)\{0,1\}|1=(\1) 2=(\2)|'
1=() 2=(:/sbin:/bin:/usr/sbin:/usr/bin)