Re: Regular Expression matching operation =~

[Grisha Levit]

On Sun, Sep 22, 2019 at 9:02 PM Allodoxaphobia <trepidation@example.net> wrote:
>
> In moving a bash ver. 4.3.48 (Ubuntu) program to a bash ver. 5.0.11
> (FreeBSD) environment I encountered either a bug, a quirk, or
> an undocumented feature.
>
> I was using a null regexp as a "match for anything" case

This behavior depends on the OS's underlying regex implementation.
For example BSD says (man 3 regex, under IMPLEMENTATION CHOICES):

    An empty parenthesized subexpression, `()', is legal and matches an empty
    (sub)string.  An empty string is not a legal RE.