Shell scripts to convert file names to lower case and upper case

To convert to lower case:

#!/bin/sh
for i in *
do
j=`echo $i | tr '[A-Z]' '[a-z]'`
mv $i $j
done

And to upper case:

#!/bin/sh
for i in *
do
j=`echo $i | tr '[a-z]' '[A-Z]'`
mv $i $j
done