zsh: directory bookmarks

change_directory_bookmarks.sh

## directory bookmarks
DB_HISTORY=~/.directory_bookmarks
function _cdb_list() {
    local I=1
    while read LINE;
    do
	printf "%2d %s\n" ${I} ${LINE}
	((I++))
    done < $DB_HISTORY
    unset LINE
}
function cdb() {
    local USAGE='usage: cdb [command] [bookmark number]'

    if [ $# = 0 ]
    then
	_cdb_list
    elif [ $# = 1 ]
    then
	case $1 in
	    add)
		touch $DB_HISTORY
		echo `pwd` >> $DB_HISTORY
		;;
	    list | ls)
		_cdb_list
		;;
	    edit)
		local E='vi'
		if [[ -n $EDITOR ]]
		then
		    E=$EDITOR
		fi
		$E $DB_HISTORY
		;;
	    *)
		expr ${1} + 1 > /dev/null 2>&1
		if [ $? -lt 2 ]
		then
		    local I=1
		    while read LINE
		    do
			if [ ${1} -eq $I ]
			then
			    cd $LINE
			fi
			((I++))
		    done < $DB_HISTORY
		    unset LINE
		else
		    echo $USAGE
		    return 1
		fi
		;;
	esac
    fi
}