Today I learned that in *nix that [ is a program and not just a bracket. it has a filepath
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Most shells also have built-in versions of many standard commands including [ and there are usually assorted differences between those and the executables.
In Bash, you should use the built-in `type` instead of `which` so that it tells you if the command is really built-in.
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unix.stackexchange.com/questions/5005 is an odd example.
Linux distributions usually don't include it but it's needed for POSIX compliance and has some super niche use cases.
