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From: wcs@ho95e.UUCP
Newsgroups: comp.unix.questions,comp.unix.wizards
Subject: Re: Re: Prompt changing on the fly
Message-ID: <1308@ho95e.ATT.COM>
Date: Mon, 2-Feb-87 18:43:56 EST
Article-I.D.: ho95e.1308
Posted: Mon Feb  2 18:43:56 1987
Date-Received: Tue, 3-Feb-87 22:37:09 EST
References: <432@ethz.UUCP> <2935@diku.UUCP>
Reply-To: wcs@ho95e.UUCP (46133-#Bill.Stewart,2G202,x0705,)
Distribution: world
Organization: AT&T Bell Labs 46133, Holmdel, NJ
Lines: 28
Xref: watmath comp.unix.questions:886 comp.unix.wizards:795

In article <2935@diku.UUCP> storm@diku.UUCP writes:
>In article <432@ethz.UUCP> wyle@ethz.UUCP (Mitchell Wyle) writes:
>>Does anyone out there have a shell script / program to change
>>the prompt DYNAMICALLY after each [CR]?
>
>You cannot use a shell script or a program to change the shell prompt
>dynamically, because the PS1/prompt variables are local to the shell,
>and therefore they can only be changed by the shell itself.  

If all you want to do is set the prompt based on a few variables (process id,
current directory, some-shell-variable, history-number), ksh and csh have some
hooks to do these.  I don't know csh, but I've seen people whose prompt
includes a number incremented by 1 each command; makes it easier to use csh's
boring version of history.

Ksh (which is upward-compatible with sh, and has decent history), allows you to
evaluate variables each time you access PS1.  Thus, my PS1 is set to
	PS1='e!!${PWD}> '
which looks like
	e!/usr/spool/news>
(the ! is doubled to prevent csh-like history-number substitution)
I don't think you can do execution at the prompt (which would be really slow),
but the newer versions of ksh let you set SECONDS to get a crude clock.
	SECONDS=0; export SECONDS
	PS1='Logged in $SECONDS: '
You can also set MAILPATH to check files other than just $MAIL.
-- 
# Bill Stewart, AT&T Bell Labs 2G-202, Holmdel NJ 1-201-949-0705 ihnp4!ho95c!wcs