[TUHS] Bourne shell and comments

Sven Mascheck mascheck at in-ulm.de
Thu Apr 20 07:02:24 AEST 2017


On Wed, Apr 19, 2017 at 06:48:34AM +1000, Warren Toomey wrote:
> I was trying to configure C news on 2.9BSD today and I found that its
> Bourne shell doesn't grok # comments. The Bourne shell in 2.11BSD does.
> 
> So I thought: when did the Bourne (and other) shells first grok # as
> indicating a comment? Was this in response to #! being added to the
> kernel, or was it the other way around? And was the choice of #!
> arbitrary, or was it borrowed from somewhere else?
> 
> Datum point: 2.9BSD's kernel can recognise #!, but the sh can't recognise #.

Dennis' email about #! to Berkeley is dated Jan 10 '80.
I've never seen any hint, how the bang in #! was chosen. Looks racy at least..
#! on BSDs was available as compile time option in 4.0BSD (~Oct '80?)
and default on 4.2BSD (~Sep '83).
BTW, AFAIK, the #! implementation in 2.8BSD (compile time option) is not
from research but seems to come from U.S. Geological Survey, Menlo Park.

The BSD csh hack in sh&csh (# special as first character in a file, service.c),
came with 3BSD, also in '80.

I found # as comment character in the BSD-sh first in CSRG 4.1.snap
(~Apr '81, word.c). And at Bell Labs, as mentioned, it came with SysIII, also ~81.
BTW, 4.3BSD ('86), and thus 2.10 BSD, brought an interesting change:
# is only recognized in non-interactive mode. In interactive mode
you actually get this:
  $ # echo x
  #: not found
This was not changed in 4BSD until sh was replaced by ash in 4.3 Net/2.

Sven
-- 
https://www.in-ulm.de/~mascheck/bourne/
https://www.in-ulm.de/~mascheck/various/shebang/


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