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From: allbery@NCoast.ORG (Brandon S. Allbery KB8JRR)
Newsgroups: comp.unix.shell
Subject: Re: Understanding the Bourne Shell (was Re: Finding the last arg)
Message-ID: <1991Jan11.035416.18772@NCoast.ORG>
Date: 11 Jan 91 03:54:16 GMT
References: <1020@mwtech.UUCP> <443@minya.UUCP> <1033@mwtech.UUCP>
Reply-To: allbery@ncoast.ORG (Brandon S. Allbery KB8JRR)
Followup-To: comp.unix.shell
Organization: North Coast Computer Resources (ncoast)
Lines: 32

As quoted from <1033@mwtech.UUCP> by martin@mwtech.UUCP (Martin Weitzel):
+---------------
| In some sense, this are the "laws of nature" as derived from observing
| the shell's behaviour. As the shell is not really nature but the outcome
| of the thoughts of some human beeing, we could of course complain now
| that this is "illogical" (compared to our sense logic!) or that there
| are "too many exceptions" and that it could be simplified with fewer,
| but more general rules.
| 
| But when thinking how to smoothen things out by using fewer rules, we
| often do not recognize all the consequences that this would have.
+---------------

There is one other problem.  I daresay it would be possible to make Bourne
shell syntax a bit more "regular" by using a yacc grammar.  THIS WON'T WORK!
At least, not without making the shell much less useful --- yacc (or other
parser generators) grammars are not designed for interaction.  In order to
do interaction *well*, the shell needs to be able to have at least some idea
of what is going on *without* having read an entire complex command (read
"if/while/for/case/etc.").  I've tried writing a yacc grammar that does this
kind of thing in a graceful manner; I ended up using context-sensitive hacks,
which I dislike in otherwise simple parsers.  This is also why csh is not
actually like C --- C can depend on the parser collecting statements for it,
but csh is primarily designed for interactive use and therefore must be able
to keep track of what's going on incrementally.

++Brandon
-- 
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