Why do people use: if [ "x$FOO" = "x" ] .... ?

[L.M.McLoughlin]

In article <361 at ho95b.UUCP> wcs at ho95b.UUCP writes:
>
>	I've seen a lot of Bourne shell scripts that test for
>blank variables using the construct
>	if [ "x$FOO" = "x" ]
>
...
>	if [ "$FOO" = "" ]
>or
>	if [ -z "$FOO" ]

How about:
	case "$FOO"
	in
	'') echo ALL GONE;;
	*) echo Something here;;
	esac

Unless you have '[' built into your shell this is generally a lot faster
but maybe less readable.

I too used to use the "x$VAR" type tests and kicked myself when I saw the
case equivalent in the rn sources.