14 Jul
2016
14 Jul
'16
8:38 p.m.
On 14/07/2016 17:11, schoedel(a)kw.igs.net wrote:
On Thu, 14 Jul 2016 16:18:43 +0300, Diomidis Spinellis
wrote
Thank you! So:
- if(1) gets as arguments an expression to evaluate and the command to
execute if the expression is true, and
- goto(1) changes the seek offset of the shared standard input file
descriptor to match the label's position in the file.
This is a much simpler implementation that what I thought would be the
case, but, true to the spirit of Unix, remarkably effective.
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.
http://www.tuhs.org/cgi-bin/utree.pl?file=V6/usr/source/s1/if.c
http://www.tuhs.org/cgi-bin/utree.pl?file=V6/usr/source/s1/goto.c