Re: Extending regexes

[Peter Stephenson <p.w.stephenson@ntlworld.com>]

> On 04 July 2022 at 13:03 Sebastian Gniazdowski <sgniazdowski@gmail.com> wrote:
> Hi,
> Zsh has extensions to regular regexes - the ~ and ^ negations.
> 
> Therefore I thought that it's weird that such an useful feature is missing
> from the commonly used regex syntax. So maybe an attempt of updating it has
> sense?

You're quite right both that they're very useful in zsh and there's nothing
like this in normal regular expressions, but unfortunately I've got a strong
feeling this is a big can of worms [hope that image is graphic enough that
I don't need to explain the phrase for non-native English speakers].

I say that as although I'm not very up on the mathematics of regular expressions
I did write the basics of the current zsh implementation of glob negations.
(Before that, there was an even less efficient implementation that created a
structure for each part of the pattern, which wasn't good for memory management
--- this is going back to the 1990s, I think.)  There are some pretty pathological
details to make sure this works in every case, so I'd really want a real expert in
the subject area to think about this before it got much further.

pws