From mboxrd@z Thu Jan  1 00:00:00 1970
From: dds@aueb.gr (Diomidis Spinellis)
Date: Thu, 14 Jul 2016 16:18:43 +0300
Subject: [TUHS] Shell control through external commands
Message-ID: <4fcf31ef-50af-10b5-0c34-ad647ed10a4e@aueb.gr>

I remember hearing that originally the Unix shell had control structures 
(e.g. if, while, case) implemented through external commands.  However, 
I can't see this reflected in the source code.  The 7th Edition Bourne 
shell has these commands built-in (usr/src/cmd/sh/cmd.c), while the 6th 
Edition (usr/source/s2/sh.c) seems to lack them completely.

The only external command I found was glob, which performed wildcard 
expansion.

Am I missing something?  Was this implemented in a version that was 
never released?  If so, does anyone know how this implementation worked? 
  (Nested commands might require holding some sort of globally 
accessible stack.)