cd es un comando de shell integrado.
$ type cd
cd is a shell builtin
Puede abrir una página de ayuda para cd en Bash con
$ help cd
Que muestra actualmente (Ubuntu 16.04):
$ help cd
cd: cd [-L|[-P [-e]] [[email protected]]] [dir]
Change the shell working directory.
Change the current directory to DIR. The default DIR is the value of the
HOME shell variable.
The variable CDPATH defines the search path for the directory containing
DIR. Alternative directory names in CDPATH are separated by a colon (:).
A null directory name is the same as the current directory. If DIR begins
with a slash (/), then CDPATH is not used.
If the directory is not found, and the shell option `cdable_vars' is set,
the word is assumed to be a variable name. If that variable has a value,
its value is used for DIR.
Options:
-L force symbolic links to be followed: resolve symbolic links in
DIR after processing instances of `..'
-P use the physical directory structure without following symbolic
links: resolve symbolic links in DIR before processing instances
of `..'
-e if the -P option is supplied, and the current working directory
cannot be determined successfully, exit with a non-zero status
[email protected] on systems that support it, present a file with extended attributes
as a directory containing the file attributes
The default is to follow symbolic links, as if `-L' were specified.
`..' is processed by removing the immediately previous pathname component
back to a slash or the beginning of DIR.
Exit Status:
Returns 0 if the directory is changed, and if $PWD is set successfully when
-P is used; non-zero otherwise.
Desafortunadamente, no responde a sus preguntas. Hay es sin embargo, la documentación que lo hace.
Puedes llegar a él con
$ man builtins
Abre muchas páginas de ayuda con less , mi visor predeterminado. Puedo encontrar la ayuda para cd presionando / y luego escribe cd , luego Enter y presionando n dos veces me lleva a la tercera instancia de la subcadena y la ayuda, que dice:
cd [-L|[-P [-e]] [[email protected]]] [dir]
Change the current directory to dir. if dir is not supplied,
the value of the HOME shell variable is the default. Any addi‐
tional arguments following dir are ignored. The variable CDPATH
defines the search path for the directory containing dir: each
directory name in CDPATH is searched for dir. Alternative
directory names in CDPATH are separated by a colon (:). A null
directory name in CDPATH is the same as the current directory,
i.e., ``.''. If dir begins with a slash (/), then CDPATH is not
used. The -P option causes cd to use the physical directory
structure by resolving symbolic links while traversing dir and
before processing instances of .. in dir (see also the -P option
to the set builtin command); the -L option forces symbolic links
to be followed by resolving the link after processing instances
of .. in dir. If .. appears in dir, it is processed by removing
the immediately previous pathname component from dir, back to a
slash or the beginning of dir. If the -e option is supplied
with -P, and the current working directory cannot be success‐
fully determined after a successful directory change, cd will
return an unsuccessful status. On systems that support it, the
[email protected] option presents the extended attributes associated with a
file as a directory. An argument of - is converted to $OLDPWD
before the directory change is attempted. If a non-empty direc‐
tory name from CDPATH is used, or if - is the first argument,
and the directory change is successful, the absolute pathname of
the new working directory is written to the standard output.
The return value is true if the directory was successfully
changed; false otherwise.
Busca el - argumento sobre la séptima línea desde el final:
Un argumento de - se convierte a $OLDPWD antes de intentar el cambio de directorio.
Tenga en cuenta que no hay -- argumento, lo que parece significar que en realidad lo ignora.
cd no es un comando, está integrado en su shell. Esto es necesario porque su directorio de trabajo actual está controlado por PWD variable de entorno con el nombre de pwd o comando "imprimir directorio de trabajo".
Las variables de entorno de un proceso padre no pueden ser modificadas por un proceso hijo. Entonces, si su shell ejecutó /bin/cd que cambió PWD solo afectaría a /bin/cd y todo lo que corrió. No cambiaría el PWD del shell .
Algunos sistemas, como OS X y CentOS, mapean el cd página man a builtin que enumera todas las funciones integradas de shell y le permite saber que debe consultar la página de manual de su shell.
Puedes comprobar qué shell tienes con echo $SHELL , probablemente sea bash .