[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.

  • Daniel Quinn@lemmy.caOP
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    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
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      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
      
      • Daniel Quinn@lemmy.caOP
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        1 year ago

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