echo "$i" | tr 123456789 abcdefghi

echo "1" | tr 0123456789 abcdefghi

echo "$i" | tr 01234567891011121314151617181920212223 abcdefghijklmnopqrstuvwxyz

echo "$i" | awk 'chr($1+48)' # This only handles the numbers
echo "$i" | awk 'chr($1+87)' # This only handles lowercase

echo -e "x41x42x43"

ABC