Re: How can I get a random number in a UNIX shell script???

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From: scriptOmatic <ScriptOmatic@ChironComputing.Com>
Date: Fri, 18 Apr 2003 22:21:05 GMT

"Dr. David Kirkby" wrote:
>
> I've written a UNIX shell script
> http://www.medphys.ucl.ac.uk/~davek/teston
>
> that allows me to copy a software package to a remote machine, then
> try to configure and build the software on that remote host. So I
> might do something like this, to check package package-foo.tar.gz on 3
> machines with 4 different configuration options, with the -T option
> saying to do this is a unique directory.
>
> teston host1 -T package-foo
> teston host1 -c '--with-threads' -T package-foo
> teston host1 -c '--with-mpi' -T package-foo
> teston host1 -c '--without-gsl' -T package-foo
>
> teston host2 -T package-foo
> teston host2 -c '--with-threads' -T package-foo
> teston host2 -c '--with-mpi' -T package-foo
> teston host2 -c '--without-gsl' -T package-foo
>
> teston host3 -T package-foo
> teston host3 -c '--with-threads' -T package-foo
> teston host3 -c '--with-mpi' -T package-foo
> teston host3 -c '--without-gsl' -T package-foo
>
> so package-foo.tar.gz gets configure/built on 3 hosts, with 4
> different options to the configure script, in ****hopefully**** 4
> different directories on each host.
>
> My problem is that I need to put each set of file into a separate
> directory, as otherwise they mess each other up. Currently I'm using
> as a directory $HOME/$REMOTE_HOSTNAME/$PID, where $PID is the PID on
> the local machine from where this is started. There is no risk of
> files from host1 interfering with those of host2, since they are in
> different directories. But there is nothing preventing those with each
> different configuration option screwing each other up on the same
> host, as I can't guarantee the PIDs will be different each time.
>
> Hence I want a random number that is portable, so not relying on perl
> or /dev/random. It doesn't need to by crytograpically secure, but
> hopefully the risk of it producing the same number on the one system
> is very small (say < 1 in 10^5).
>
> I don't want to use the systems 'rand' (or similar) and seed it from
> the system's clock, since if these scripts are run in parallel (which
> is what I would do on a multi-processor machine), there is every
> chance that they will be seeded with the same number, as they would
> start at the same time.
>
> Any thoughts? Perhaps the PID is reasonable, given the consequences
> for it going wrong are not that huge, but I'd like to make it a bit
> more robust, if only for peace of mind.
>
> --
> Dr. David Kirkby,
> Senior Research Fellow,
> Department of Medical Physics,
> University College London,
> 11-20 Capper St, London, WC1E 6JA.
> Tel: 020 7679 6408 Fax: 020 7679 6269
> Internal telephone: ext 46408
> e-mail davek@medphys.ucl.ac.uk

/bin/ksh supports ${RANDOM} which is always some random number.
Your shell is /bin/sh but you could simply do this
RANDOM=`/bin/ksh -c 'echo $RANDOM'`

-- 
http://ftp.opensysmon.com is a shell script archive site with an
open source system monitoring and network monitoring software package.
Many platforms are supplied already compiled.

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• In reply to: Dr. David Kirkby: "How can I get a random number in a UNIX shell script???"
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