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From: rouben@math9.math.umbc.edu (Rouben Rostamian)
Newsgroups: comp.unix.questions
Subject: Re: csh quoting question: nested command substitution
Message-ID: <3656@umbc3.UMBC.EDU>
Date: 26 Jul 90 04:00:56 GMT
References: <4031@rodan.acs.syr.edu>
Sender: newspost@umbc3.UMBC.EDU
Reply-To: rouben@math9.math.umbc.edu.UUCP (Rouben Rostamian)
Organization: Mathematics Department University of Maryland, Baltimore County
Lines: 32

In article <4031@rodan.acs.syr.edu> jdpeek@rodan.acs.syr.edu (Jerry Peek) writes:
 >Okay, I can tell that I obviously don't understand csh quoting.
 >I want to set the csh prompt, but this question is really more generic
 >than prompt-setting.
 >
 >In the Bourne shell, I can do:
 >	PS1="`/bin/expr \`/bin/hostname\` : '\([^.]*\)'`$ "
 >which runs basename, then strips off anything after the local host name.
 >So, if /bin/hostname prints rodan.acs.syr.edu, the prompt is rodan$.
 >And, if /bin/hostname prints rodan, the prompt is still rodan$.
 >
 >I know there are lots of other ways to do this (pipe to sed, store
 >hostname output in a shell variable first, etc.).
 >But I want to do it in csh, in a nice one-liner like sh lets me.
 >No matter what I do, I get some kind of syntax error.
 >Can someone at least tell me how... and, better, tell me *why*?  Thanks.

In csh you achieve the same effect by:

   set prompt = `/bin/hostname | /usr/bin/cut -d. -f1`'$ '

I do not know why your expr syntax does not work in csh.  In fact, I am
surprised that the nested expression evaluation with ` ` works in sh
to begin with.  Does sh make two passes, first evaluating /bin/hostname
and then executing expr?  

--
 
Rouben Rostamian                               Telephone: (301) 455-2458
Department of Mathematics and Statistics       e-mail:
University of Maryland Baltimore County        rostamian@umbc.bitnet
Baltimore, MD 21228,  U.S.A.                   rostamian@umbc3.umbc.edu