[TUHS] Shell control through external commands

Sven Mascheck mascheck at in-ulm.de
Tue Sep 13 10:17:55 AEST 2016


On Mon, Sep 12, 2016 at 02:50:10PM +0200, Joerg Schilling wrote:
> > > The colon was introduced by AT&T around 1983.
> > 
> > It's a builtin in the v7 Bourne shell - see SYSNULL in msg.c (which
> > has the command name table) and in xec.c (which has the implementation)
> 
> You are missinterpeting things.
> 
> The colon in line one as a hint to a modified csh to call the Bourne Shell  
> first appeared around 1983.

I'm still confused (you're short with context): what does "introduced by AT&T" mean?

I only know the #-hacked csh from 2BSD+ ('79), and the #-hacked sh from 3BSD+ ('80).
How would ":" as a hint in this respect show up on other systems?


BTW: academic but funny side effect of : as no-op instead of real comment:

: `echo output 1>&2`

actually writes to stderr.


Normal Wilson wrote:

> [...] A hack emerged: if csh encountered a script file, it would read the
> first character; if that was '#' it was a csh script, otherwise it handed
> off to /bin/sh.

lesser known fact: even sh was hacked on BSDs (since 3BSD) with this #-csh magic,
and also exec'ed to csh. This then co-existed with the soon coming implementation
of "#" as comment character.

-Sven


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