[pxc]

I'm not sure why you would. I don't think POSIX generally specifies the behavior of command line tools in such a level of detail. FWIW, the regex type used by default by GNU Grep is already POSIX's Basic Regular Expressions. (It also supports POSIX Extended Regular Expressions and PCRE2.)

Afaik, EulerOS and other Unix-certified Linux distros just ship the usual GNU userland.

[mdasen]

The Single UNIX Specification does specify the behavior of many command line tools like ed, grep, awk, etc. OpenBSD sometimes notes where their tools vary from the UNIX spec. It's usually very small ways that don't matter to most people, but it does put them outside of the UNIX spec.

[swiftcoder]

POSIX != Unix. Unix certification does require POSIX, but it also comes with a bunch more stringent requirements

[pxc]

My mistake! Thanks for informing me :)