[U-Boot] [PATCH] cmd_nvedit.c: Add env exists command

[Andrew Ruder <andy@aeruder.net>]

On Wed, Oct 23, 2013 at 06:55:02AM -0700, James Chargin wrote:
> I have, more recently, been using scripting of the form
> 
> 	if test "X" != "X${var}"; then
> 		echo defined
> 	else
> 		echo undefined
> 	fi

Thanks for the feedback.

I was attempting to do something like that originally but was hitting
problems related to the expansion which I'm still tracking down:

   WRONG:
   $ set var
   $ test "x${var}" = "x" && echo undefined
   undefined
   $ set var 1
   $ test "x${var}" = "x" && echo undefined
   $ set var "1; 2; 3"
   $ test "x${var}" = "x" && echo undefined
>> undefined

It DOES seem to work a lot better with != as you mentioned above
though...

   RIGHT:
   $ set var
   $ test "x${var}" != "x" && echo defined
   $ set var 1
   $ test "x${var}" != "x" && echo defined
   defined
   $ set var "1; 2; 3"
   $ test "x${var}" != "x" && echo defined
   defined

- Andy