What shells fail to work if comparing with "" ?

[Dr. David Kirkby]

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

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?



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Dave