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From: wcs@ho95b.UUCP (Bill Stewart)
Newsgroups: net.unix
Subject: Why do people use:  if [ "x$FOO" = "x" ] .... ?
Message-ID: <361@ho95b.UUCP>
Date: Tue, 9-Apr-85 00:37:49 EST
Article-I.D.: ho95b.361
Posted: Tue Apr  9 00:37:49 1985
Date-Received: Tue, 9-Apr-85 08:41:00 EST
Organization: AT&T Bell Labs, Holmdel NJ
Lines: 20


	I've seen a lot of Bourne shell scripts that test for
blank variables using the construct
	if [ "x$FOO" = "x" ]

Why the x's?  If you leave out the quotes, then the test dies if $FOO
is empty, but why not just use
	if [ "$FOO" = "" ]
or
	if [ -z "$FOO" ]

I've seen this construct in new code as well as old, from reputable
programmers.  I've checked a few obscure cases like
	FOO='`echo You Lose!!`'
but even they don't die.  Is this just another superstition, like
	sync; sync; sync;
or am I forgetting something stupid and obvious?
			Thanks;
				Bill Stewart, AT&T Bell Labs, Holmdel NJ
				{ihnp4,allegra,cbosg}!ho95c!wcs