[TUHS] Shell control through external commands

Diomidis Spinellis dds at aueb.gr
Thu Jul 14 23:18:43 AEST 2016


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.)


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