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From: tgl@zog.cs.cmu.edu (Tom Lane)
Newsgroups: comp.sys.hp
Subject: Re: HP-UX 7.0 problems with ps(1) and awk(1) in pipe
Summary: Easier to use a temp file
Message-ID: <10262@pt.cs.cmu.edu>
Date: 15 Aug 90 23:35:44 GMT
References: <90222.183205QQ11@LIVERPOOL.AC.UK> <-286539949@hpcupt1.HP.COM>
Organization: Carnegie-Mellon University, CS/RI
Lines: 35

In article <-286539949@hpcupt1.HP.COM>, jonb@hpcupt1.HP.COM (Jon Bayh) writes:
> Alan Thew of the University of Liverpool Computer Laboratory writes:
> > 
> > set exists=`ps -uqq11 | awk '$4 == "getus.csh" && $1 != x { print $1 }' x=$$ -`
> > 
> > This worked fine at HP-UX 3.1 but at 7.0 a "spurious" PID is found
> > (presumably as a result of executing part of the above pipe). The
> > resulting kill(1) fails since the process is already dead.
> 
> [Jon explains that the ps is spotting the subprocess forked to exec() awk,
>  before the latter has been able to do the exec; it still has the shell
>  script name.  He suggests a couple of rather ugly solutions.]

I've run into related problems in scripts for regular sh.  A cleaner
fix than either of Jon's is to direct ps's output into a temporary file:

	ps >/tmp/psout$$
	set exists=`awk 'awk program' </tmp/psout$$`
	rm -f /tmp/psout$$

This way there are no extra processes laying about at the instant ps runs,
so you need not worry about distinguishing them from the parent.

Incidentally, if the job you are trying to kill is a shell script, you need
to worry about making sure that what you find is the parent process, not a
subprocess ... the awk script could be extended to choose the right target
by looking at parent process IDs, but it wouldn't be a trivial change.  I
haven't drunk enough Coke yet this morning to be able to work it out :-)

-- 
				tom lane
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