From mboxrd@z Thu Jan  1 00:00:00 1970
From: random832@fastmail.com (Random832)
Date: Thu, 14 Jul 2016 22:25:31 -0400
Subject: [TUHS] Shell control through external commands
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On Thu, Jul 14, 2016, at 19:56, shawn wilson wrote:
> I've always been curious though - what was the reason behind
> implementing /bin/[ ? IDK any shell where this isn't implemented - I
> always assumed it's a POSIX compatibility stopgap older systems needed
> to stay compliant with their shipped shell.

It's required because it might be executed by non-shell programs.

http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap01.html#tag_17_06

My Mac even has /usr/bin/cd.

The "special builtins" which aren't required to exist as binaries are:  
  break : continue .  eval exec exit export readonly return set shift
times trap unset