[PATCH] ash: improve speed of variable pattern substitution

[Denys Vlasenko]

On Wed, Jul 21, 2021 at 10:54 PM Alin Mr <almr.oss at outlook.com> wrote:
>
> Ron, thanks for your quick patch and the hints. I saw your message and was thinking through;  fixed-length patterns don't need backtracking. '?' (without '*') also results in fixed-length patterns, so maybe that'd be more complicated to detect.
>
> To motivate this a bit: it started with quoters. Since we have neither bash's ${x at Q}, nor `printf %q`, it's harder to escape shell code for eval, or to produce quoted SQL values **efficiently**.

A patch to implement e.g. ${x at Q} is acceptable.