Re: What is wrong with a regex?

[Leonid Isaev]

On Sat, Feb 04, 2023 at 02:20:20PM +0900, Koichi Murase wrote:
> Bash relies on the system library <regex.h> for the regular
> expressions, so I guess the Bash version is not so much related to
> this behavior difference.

Thanks for the explanation.
 
> I also checked the behavior of Cygwin, where <regex.h> seems to be
> implemented as a part of Newlib. Newlib <regex.h> also seems to
> support an empty <ERE_branch> and thus (|_x).

FYI, on Alpine (musl libc), bash also supports empty regex branch:
-----8<-----
alp-gofax:~$ bash --version
GNU bash, version 5.2.9(1)-release (x86_64-alpine-linux-musl)
Copyright (C) 2022 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>

This is free software; you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

alp-gofax:~$ ldd /bin/bash
        /lib/ld-musl-x86_64.so.1 (0x7f39944cd000)
        libreadline.so.8 => /usr/lib/libreadline.so.8 (0x7f39943b3000)
        libc.musl-x86_64.so.1 => /lib/ld-musl-x86_64.so.1 (0x7f39944cd000)
        libncursesw.so.6 => /usr/lib/libncursesw.so.6 (0x7f3994356000)

alp-gofax:~$ f="row.txt"; [[ "$f" =~ ^r(|o)w ]]; echo "$?"; printf "%s|" 
"${BASH_REMATCH[@]}"; echo
0
row|o|
----->8-----

-- 
Leonid Isaev