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