Команда cd linux что делает

Команда cd linux что делает

NAME

cd - change the working directory

SYNOPSIS

cd [-L | -P] [directory] cd - 

DESCRIPTION

The cd utility shall change the working directory of the current shell execution environment (see Shell Execution Environment ) by executing the following steps in sequence. (In the following steps, the symbol curpath represents an intermediate value used to simplify the description of the algorithm used by cd. There is no requirement that curpath be made visible to the application.) 1. If no directory operand is given and the HOME environment variable is empty or undefined, the default behavior is implementation-defined and no further steps shall be taken. 2. If no directory operand is given and the HOME environment variable is set to a non- empty value, the cd utility shall behave as if the directory named in the HOME environment variable was specified as the directory operand. 3. If the directory operand begins with a slash character, set curpath to the operand and proceed to step 7. 4. If the first component of the directory operand is dot or dot-dot, proceed to step 6. 5. Starting with the first pathname in the colon-separated pathnames of CDPATH (see the ENVIRONMENT VARIABLES section) if the pathname is non-null, test if the concatenation of that pathname, a slash character, and the directory operand names a directory. If the pathname is null, test if the concatenation of dot, a slash character, and the operand names a directory. In either case, if the resulting string names an existing directory, set curpath to that string and proceed to step 7. Otherwise, repeat this step with the next pathname in CDPATH until all pathnames have been tested. 6. Set curpath to the string formed by the concatenation of the value of PWD , a slash character, and the operand. 7. If the -P option is in effect, the cd utility shall perform actions equivalent to the chdir() function, called with curpath as the path argument. If these actions succeed, the PWD environment variable shall be set to an absolute pathname for the current working directory and shall not contain filename components that, in the context of pathname resolution, refer to a file of type symbolic link. If there is insufficient permission on the new directory, or on any parent of that directory, to determine the current working directory, the value of the PWD environment variable is unspecified. If the actions equivalent to chdir() fail for any reason, the cd utility shall display an appropriate error message and not alter the PWD environment variable. Whether the actions equivalent to chdir() succeed or fail, no further steps shall be taken. 8. The curpath value shall then be converted to canonical form as follows, considering each component from beginning to end, in sequence: a. Dot components and any slashes that separate them from the next component shall be deleted. b. For each dot-dot component, if there is a preceding component and it is neither root nor dot-dot, the preceding component, all slashes separating the preceding component from dot-dot, dot-dot and all slashes separating dot-dot from the following component shall be deleted. c. An implementation may further simplify curpath by removing any trailing slash characters that are not also leading slashes, replacing multiple non-leading consecutive slashes with a single slash, and replacing three or more leading slashes with a single slash. If, as a result of this canonicalization, the curpath variable is null, no further steps shall be taken. 9. The cd utility shall then perform actions equivalent to the chdir() function called with curpath as the path argument. If these actions failed for any reason, the cd utility shall display an appropriate error message and no further steps shall be taken. The PWD environment variable shall be set to curpath. If, during the execution of the above steps, the PWD environment variable is changed, the OLDPWD environment variable shall also be changed to the value of the old working directory (that is the current working directory immediately prior to the call to cd).

OPTIONS

The cd utility shall conform to the Base Definitions volume of IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines. The following options shall be supported by the implementation: -L Handle the operand dot-dot logically; symbolic link components shall not be resolved before dot-dot components are processed (see steps 8. and 9. in the DESCRIPTION). -P Handle the operand dot-dot physically; symbolic link components shall be resolved before dot-dot components are processed (see step 7. in the DESCRIPTION). If both -L and -P options are specified, the last of these options shall be used and all others ignored. If neither -L nor -P is specified, the operand shall be handled dot-dot logically; see the DESCRIPTION.

OPERANDS

The following operands shall be supported: directory An absolute or relative pathname of the directory that shall become the new working directory. The interpretation of a relative pathname by cd depends on the -L option and the CDPATH and PWD environment variables. If directory is an empty string, the results are unspecified. - When a hyphen is used as the operand, this shall be equivalent to the command: cd "$OLDPWD" && pwd which changes to the previous working directory and then writes its name.

STDIN

INPUT FILES

ENVIRONMENT VARIABLES

The following environment variables shall affect the execution of cd: CDPATH A colon-separated list of pathnames that refer to directories. The cd utility shall use this list in its attempt to change the directory, as described in the DESCRIPTION. An empty string in place of a directory pathname represents the current directory. If CDPATH is not set, it shall be treated as if it were an empty string. HOME The name of the directory, used when no directory operand is specified. LANG Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume of IEEE Std 1003.1-2001, Section 8.2, Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.) LC_ALL If set to a non-empty string value, override the values of all the other internationalization variables. LC_CTYPE Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multi-byte characters in arguments). LC_MESSAGES Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error. NLSPATH Determine the location of message catalogs for the processing of LC_MESSAGES . OLDPWD A pathname of the previous working directory, used by cd -. PWD This variable shall be set as specified in the DESCRIPTION. If an application sets or unsets the value of PWD , the behavior of cd is unspecified.

ASYNCHRONOUS EVENTS

STDOUT

If a non-empty directory name from CDPATH is used, or if cd - is used, an absolute pathname of the new working directory shall be written to the standard output as follows: "%s\n", new directory> Otherwise, there shall be no output.

The standard error shall be used only for diagnostic messages.

The following exit values shall be returned: 0 The directory was successfully changed. >0 An error occurred.

The working directory shall remain unchanged. The following sections are informative. 

Since cd affects the current shell execution environment, it is always provided as a shell regular built-in. If it is called in a subshell or separate utility execution environment, such as one of the following: (cd /tmp) nohup cd find . -exec cd <> \; it does not affect the working directory of the caller's environment. The user must have execute (search) permission in directory in order to change to it.

The use of the CDPATH was introduced in the System V shell. Its use is analogous to the use of the PATH variable in the shell. The BSD C shell used a shell parameter cdpath for this purpose. A common extension when HOME is undefined is to get the login directory from the user database for the invoking user. This does not occur on System V implementations. Some historical shells, such as the KornShell, took special actions when the directory name contained a dot-dot component, selecting the logical parent of the directory, rather than the actual parent directory; that is, it moved up one level toward the '/' in the pathname, remembering what the user typed, rather than performing the equivalent of: chdir(".."); In such a shell, the following commands would not necessarily produce equivalent output for all directories: cd .. && ls ls .. This behavior is now the default. It is not consistent with the definition of dot-dot in most historical practice; that is, while this behavior has been optionally available in the KornShell, other shells have historically not supported this functionality. The logical pathname is stored in the PWD environment variable when the cd utility completes and this value is used to construct the next directory name if cd is invoked with the -L option.

Shell Execution Environment , pwd , the System Interfaces volume of IEEE Std 1003.1-2001, chdir()