---
layout: page
category-page: fs
category-title: FileSystem
tags: change directory
author: Mirko Ponzio
title: cd
---
<p> In the operative system Unix and Unix-like, and in general in the system
  POSIX, cd  (change directory) is an internal command of shell that change the
  corrent directory. <br><br>

The command is only an internal command of shell, it can't be an external program,
because one process can modified only the own corrent directory and not that of
other processes.
So the Shell has to implement this function autonomously.


La new setting of the corrent directory it has been inherited from the started
programs.
 <br> <br>

After the change of the directory, the variable pwd it is automatically updated
with the pathname of the new directory.
</p> <br> <br>

<h2> Some usefull command for CD<h2>
  <ul>
<li> cd by itself or cd ~ will always put you in your home directory.</li>
<li> cd . will leave you in the same directory you are currently in (i.e. your current directory won't change).
This can be useful if your shell's internal code can't deal with the directory you are in being recreated; running cd . will place your
shell in the recreated directory. </li>
<li> cd ~username will put you in username's home directory. </li>
<li> cd dir (without a /) will put you in a subdirectory; for example, if you are in /usr, typing cd bin will put you in /usr/bin, while cd /bin puts you in /bin.</li>
<li> cd .. will move you up one directory. So, if you are /usr/bin/tmp, cd .. moves you to /usr/bin, while cd ../.. moves you to /usr (i.e. up two levels).
  You can use this indirection to access subdirectories too. So, from /usr/bin/tmp, you can use cd ../../local to go to /usr/local.</li>
<li> cd - will switch you to the previous directory. For example, if you are in /usr/bin/tmp, and go to /etc,
  \you can type cd - to go back to /usr/bin/tmp. You can use this to toggle back and forth between two directories. </li>
</ul>

<h2> sintax of cd </h2>
<p>
La sintassi generale di cd è la seguente:

cd [opzioni] [--] [dir]
Il parametro facoltativo dir indica la nuova directory corrente. Se non è specificato, viene usato al suo posto il valore della variabile d'ambiente HOME,
che normalmente indica la home directory dell'utente. Se invece è un trattino ("-"), allora viene usata la directory corrente precedente.

Se il parametro dir è un pathname relativo che non ha come primo elemento "." o "..", allora esso viene unito a ciascuna delle directory
elencate nella variabile d'ambiente CDPATH: se il risultato corrisponde ad una directory esistente, allora essa diviene la nuova directory corrente.
Altrimenti dir viene considerato relativo alla directory corrente.

Il doppio trattino -- (facoltativo) indica che i parametri successivi non sono da considerarsi opzioni.</p>