Here's something a little more informative, if you need it, but it's in ksh. Dunno if that's normal enough for you. -e is not available in sh:

#!/bin/ksh
if [ -s /path/to/file ] ; then
echo We have a file with stuff in it
elif [ -e /path/to/file ] ; then
echo We have a file with 0-length
else
echo "The file isn't even there!"
fi

do a "man test" on a UNIX box near you.

BTW, if you're on Linux then /sbin/sh is likely really bash, and you can use the -e.