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What shells fail to work if comparing with "" ?

From: Dr. David Kirkby
Subject: What shells fail to work if comparing with "" ?
Date: Thu, 10 Feb 2011 18:56:24 +0000
User-agent: Mozilla/5.0 (X11; U; SunOS i86pc; en-US; rv: Gecko/20100214 Thunderbird/3.0.1

I know its considered bad practice to check for an empty string with something 

if [ "$STR" = "" ] ; then

but what shells do actually break with this, and under what conditions?

I was proposing someone change a test like that to

if [ "x$STR" =  ] ; then

but someone has argued against this, saying he knows of no shell where the former is not acceptable. I realise this issue is probably more of a problem with older shells, but can anyone give me any examples of where the former will break, but the latter will be ok?

A: Because it messes up the order in which people normally read text.
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