Upper to Lower Case

echo "program to convert uppercase to lower case"
echo "enter the filename to be created:"
read str
vi $str
echo "1.lowercase to uppercase"
echo "2.uppercase to lowercase"
echo "select your choice:"
read ch
case $ch in
1)cat $str | tr "{a-z}" "{A-Z}" | tee $str cat $str;;
2)cat $str | tr "{A-Z}" "{a-z}" | tee $str cat $str;;
*)echo "invalid choice"
esac