String comparisons don't work in shell scripts?

Thanks for the Hint , For whomever you wrote it it helped my purpose

In string comparisons in shell scripts, instead of using "test expression" or "[ expression ]," I suggest that folks try using the "extended test facility" (not available in all shells). The extended test facility is "[[ expression ]]," like so:

[[ $str1 < $str2 ]]

Notice that I purposely left out the backslash character before the angle bracket above. It seems to work fine on my system (OSX Snow Leopard ver. 10.6.8). The extended test facility is supposed to require less quoting (because it doesn't do word splitting or pathname expansion), and indeed, that seems to be the case here.

Notice that I've included spaces liberally around everything above. It's been my experience in working with language translators (interpreters [like the shell command interpreters] and compilers) that this helps with debugging, because it often seems to make it easier for the translator to give more meaningful error messages when it encounters a syntax error. If you compress and run things together as much as possible, with as little white space as possible, then it makes things worse--not only for the error processing routines to try and guess at what you meant, but also for humans trying to read the code!

So, I try to space things apart whenever possible; removing extra spaces only when absolutely necessary. It seems like, in some programming environments, programmers have traditionally done just the opposite. Of course, there are some situations where spaces must not be used; the trick seems to be in knowing when they're required, when they're optional, and when they must be left out.

If you happen to know for sure that spaces won't work in a particular place, then don't put them in. Otherwise, if you're not sure whether spaces will work or not, I suggest that you either put them in (and test your code accordingly) or else read enough of the documentation to determine whether to include them or leave them out in that particular place.

Note that using the extended test facility probably will make a shell script less portable. So, if portability is important to you, you probably should either do some testing on the different systems and shells you plan to use, or else stick to the other, more universal, ways of doing this, such as the "test expression" and "[ expression ]" facilities that are in most shells.

The new code then becomes:

#!/bin/sh

a="aardvark" # then try 'zebra'
b="banjo"

if [[ $a < $b ]] ; then
echo "$a is less than $b"
else
echo "$a is NOT less than $b"
fi

exit 0

The above code produced the correct output for me, both for "aardvark" and for "zebra".