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git-svn-id: svn+ssh://atelier.inf.usi.ch/home/bevilj/group-1@164 a672b425-5310-4d7a-af5c-997e18724b81
53 lines
2.7 KiB
HTML
53 lines
2.7 KiB
HTML
---
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layout: page
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category-title: fs
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category-page: FileSystem
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tags: change directory
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author: Mirko Ponzio
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title: cd
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---
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<p> In the operative system Unix and Unix-like, and in general in the system
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POSIX, cd (change directory) is an internal command of shell that change the
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corrent directory. <br><br>
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The command is only an internal command of shell, it can't be an external program,
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because one process can modified only the own corrent directory and not that of
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other processes.
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So the Shell has to implement this function autonomously.
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La new setting of the corrent directory it has been inherited from the started
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programs.
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<br> <br>
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After the change of the directory, the variable pwd it is automatically updated
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with the pathname of the new directory.
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</p> <br> <br>
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<h2> Some usefull command for CD<h2>
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<ul>
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<li> cd by itself or cd ~ will always put you in your home directory.</li>
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<li> cd . will leave you in the same directory you are currently in (i.e. your current directory won't change).
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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
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shell in the recreated directory. </li>
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<li> cd ~username will put you in username's home directory. </li>
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<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>
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<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).
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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>
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<li> cd - will switch you to the previous directory. For example, if you are in /usr/bin/tmp, and go to /etc,
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\you can type cd - to go back to /usr/bin/tmp. You can use this to toggle back and forth between two directories. </li>
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</ul>
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<h2> sintax of cd </h2>
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<p>
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La sintassi generale di cd è la seguente:
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cd [opzioni] [--] [dir]
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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,
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che normalmente indica la home directory dell'utente. Se invece è un trattino ("-"), allora viene usata la directory corrente precedente.
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Se il parametro dir è un pathname relativo che non ha come primo elemento "." o "..", allora esso viene unito a ciascuna delle directory
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elencate nella variabile d'ambiente CDPATH: se il risultato corrisponde ad una directory esistente, allora essa diviene la nuova directory corrente.
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Altrimenti dir viene considerato relativo alla directory corrente.
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Il doppio trattino -- (facoltativo) indica che i parametri successivi non sono da considerarsi opzioni.</p>
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