Redifines the change directory command /cd/. When using /cd/ without parameters, instead of changing to home directory, /cd/ will output the latest directories you visited and let you change directory using an index number.
/etc/X11/xkb$ cd
1 /usr/include/linux/android
2 /usr/include/linux/mmc
3 /usr
4 /usr/local
/etc/X11/xkb$ cd 4
/usr/local$ cd
1 /etc/X11/xkb
2 /usr/include/linux/android
3 /usr/include/linux/mmc
4 /usr
5 /usr/local