Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!gem.mps.ohio-state.edu!tut.cis.ohio-state.edu!bloom-beacon!snorkelwacker!spdcc!ima!cfisun!lakart!dg
From: dg@lakart.UUCP (David Goodenough)
Newsgroups: comp.unix.questions
Subject: Re: Lock Files From Shell Scripts
Message-ID: <741@lakart.UUCP>
Date: 8 Nov 89 18:23:57 GMT
References: <1691@ncrcce.StPaul.NCR.COM>
Organization: Lakart Corporation, Newton, MA
Lines: 47

mercer@ncrcce.StPaul.NCR.COM (Dan Mercer) sez:
> ..... Then I considered using ln,  thinking an error
> condition would be returned if the file existed.  But no,  the file
> was overwritten unconditionally.

Humm - sounds like SYSV and a funky ln. However, if mkdir will overwrite
an already existing directory then I'd say you have a really badly broken
system. So why not:

--- cut here --- cut here --- cut here --- cut here --- cut here ---
lock=/tmp/lock

until mkdir $lock 2>&1 >/dev/null
do
    sleep 10
done

# critical stuff

# clean up the lock directory
rmdir $lock

exit 0
--- cut here --- cut here --- cut here --- cut here --- cut here ---

You could also use umask and touch, except touch doesn't return an error
status, at least BSD touch doesn't (again, if mkdir doesn't you're in
dead trouble anyway)
-- 
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