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From: guy@sun.uucp (Guy Harris)
Newsgroups: net.unix-wizards
Subject: Re: comm '! sort file1' '! sort file2'
Message-ID: <8086@sun.uucp>
Date: Sat, 11-Oct-86 02:05:08 EDT
Article-I.D.: sun.8086
Posted: Sat Oct 11 02:05:08 1986
Date-Received: Sat, 11-Oct-86 21:23:10 EDT
References: <830003@hpcnoe.UUCP> <35@pixutl.UUCP> <3724@umcp-cs.UUCP> <264@desint.UUCP> <7028@elsie.UUCP>
Organization: Sun Microsystems, Inc.
Lines: 22

> Think of the havoc that results if I put a
> 	sort "$1" > ~/fifo & sort "$2" | comm - ~/fifo
> command into a shell script (named, for example, "scomm") and then,
> six months from now when I've forgotten the implementation details,
> type in
> 	scomm firstfile secondfile > results &
> 	scomm thirdfile fourthfile > moreresults &

At which point you say "Since the FIFO is a temporary file, I shouldn't just
save a FIFO in my home directory for a rainy day and use that; I should
create it at the beginning of the script, using "$$" in the name to make the
name unique, and delete it at the end!" and change the script to read like:

	fifoname=/tmp/scomm.$$
	trap "rm -f $fifoname; exit 1" 1 2 15
	/etc/mknod $fifoname p
	sort "$1" > $fifoname & sort "$2" | comm - $fifoname
	rm -f $fifoname
-- 
	Guy Harris
	{ihnp4, decvax, seismo, decwrl, ...}!sun!guy
	guy@sun.com (or guy@sun.arpa)