cd(){    case "$#" in        0 | 1)  builtin cd $1 ;;        2    )  newdir=$(echo $PWD | sed -e "s:$1:$2:g")                case "$newdir" in                    $PWD)   echo "bash: cd: bad substitution" >&2 ; return 1 ;;                    *   )   builtin cd "$newdir" ;;                esac ;;        *    )  echo "bash: cd: wrong arg count" 1>&2 ; return 1 ;;    esac}