[TUHS] Shell control through external commands

[Tony Finch]

Dave Horsfall <dave at horsfall.org> wrote:
> On Thu, 14 Jul 2016, Clem Cole wrote:
>
> > Could you be confusing the fact the true and false were implemented by
> > external commands in some early shell's
>
> And on the Mac and FreeBSD, they still are (as well as being builtins).
> At one time they were shell scripts e.g. "exit 0" for "true".

This isn't a BSDism: POSIX requires that most built-in commands also exist
as executables on the PATH. The exceptions are the "special built-in
commands" which manipulate the shell command language state, e.g. break
and set.

http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_14

Tony.
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