submitted 1 year ago by danielquinn@lemmy.ca to c/linux@lemmy.ml

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[For reference, I'm talking about Ash in Alpine Linux here, which is part of BusyBox.]

I thought I knew the big differences, but it turns out I've had false assumptions for years. Ash does support [[ double square brackets ]] and (as best I can tell) all of Bash's logical trickery inside them. It also supports ${VARIABLE_SUBSTRINGS:5:12}` which was another surprise.

At this stage, the only things I've found that Bash can do that Ash can't are:

Arrays, which Bash doesn't seem to do well anyway
Brace expansion, which is awesome but I can live without it.

What else is there? Did Ash used to be more limited? The double square bracket thing really surprised me.

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[-] danielquinn@lemmy.ca 3 points 1 year ago

Yup, that looks like exactly what was done in Alpine:

$ docker run --rm -it alpine ls -l /usr/bin/[[
lrwxrwxrwx    1 root     root            12 Sep 28 11:18 /usr/bin/[[ -> /bin/busybox

So while the Ash itself doesn't support the [[ extension, this work-around produces the same effect. Nifty.

[-] jntesteves@lemmy.world 5 points 1 year ago

Although that link exists, that's not what is being used by default. [[ is a shell builtin in ash/busybox, so that takes precedence.

On Alpine:

❯ which [[
/usr/bin/[[

❯ command -V [[
[[ is a shell builtin

[-] danielquinn@lemmy.ca 1 points 1 year ago

Huh. So the link is unnecessary and Ash supports [[ out of the box? Good to know, thanks!

this post was submitted on 02 Nov 2023

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