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@Q}, nor `printf %q`, it's harder to escape shell code for eval, or to
produce quoted SQL values **efficiently**.
I'm working on a shell logging wrapper (fakesh.sh:
https://gitlab.com/kstr0k/f8ksh) which logs all shell invocations, with start /
end timestamps. This came about because Kakoune (the editor) uses POSIX shell
as an extension language (and so does most of its plugin ecosystem). So,
hundreds of tiny shell calls / second.
As I expected, switching from dash to "applet-biased" busybox (STANDALONE +
PREFER_APPLETS) makes a big difference. So I invested a bit of effort into
making busybox available for users (I have a setup script that can compile, or
download and extract directly from distro packages:
https://gitlab.com/kstr0k/f8ksh/-/blob/master/setup-bbox).
fakesh.sh produces '<<EOF'-escaped log files that are also shell code (fastest
to produce, but verbose); these are later parsed to SQL. The log converter
(itself running under BusyBox) was pretty slow, so I switched to ${x///}. But
this made the converter even slower. This is how I got here.
Busybox is an amazing tool. I've known it since my embedded days, but it turns
out that, with builtin coreutils (no external calls), it can work as a very
effective extension language. It would be nice to make even more applets nofork
(e.g. sed is currently a "runner", and I understand why, but that's too bad for
scripts that just use it to munge strings).
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