Title : A few tips about the cd command
Author: Solène
Date  : 04 September 2020
Tags  : unix

While everyone familiar with a shell know about the command `cd`
there are a few tips you should know.

### Moving to your $HOME directory

    $ pwd
    $ cd
    $ pwd

Using `cd` without argument will change your current directory to
your $HOME.

### Moving into someone $HOME directory

While this should fail most of the time because people shouldn't allow
anyone to visit their $HOME, there are use case it can be used though.

    $ cd ~user1
    $ pwd
    $ cd ~solene
    $ pwd

Using `~user` as a parameter will move to that user $HOME directory,
note that `cd` and `cd ~youruser` have the same result.

### Moving to previous directory

This is a very useful command which allow going back and forth between
two directories.

    $ pwd
    $ cd /tmp
    $ pwd
    $ cd -
    $ pwd

When you use `cd -` the command will move to the previous directory
in which you were. There are two special variables in your shell:
`PWD` and `OLDPWD`, when you move somewhere, `OLDPWD` will hold
your current location before moving and then `PWD` hold the new
path. When you use `cd -` the two variables get exchanged, this
mean you can only jump from two paths using `cd -` multiple times.

Please note that when using `cd -` your new location is displayed.

### Changing directory by modifying current PWD

thfr@ showed me a cd feature I never heard about, and it's the
perfect place to write about it. Note that this work in ksh and zsh
but is reported to not work in bash.

One example will explain better than any text.

    $ pwd
    $ cd 1.2.0 2.4.0

This tells `cd` to replace first parameter pattern by the second
parameter in the current `PWD` and then cd into it.

    $ pwd
    $ cd solene user1

This could be done in a bloated way with the following command:

    $ cd $(echo $PWD | sed "s/solene/user1/")

I learned it a few minutes ago but I see a lot of uses cases where
I could use it.

### Moving into the current directory after removal

In some specific case, like having your shell into a directory that
existed but was deleted and removed (this happens often when you
working into compilation directories).

A simple trick is to tell `cd` to go to the current location.

    $ cd .


    $ cd $PWD

And `cd` will go into the same path and you can start hacking
again in that directory.