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PROGRAM:

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 Section 2.12, 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 if that pathname did not end with 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 directory operand.

7. If the −P option is in effect, proceed to step 10. If curpath does not begin with a
<slash> character, set curpath to the string formed by the concatenation of the value
of PWD, a <slash> character if the value of PWD did not end with a <slash> character,
and curpath.

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 <slash> characters 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, then:

i. If the preceding component does not refer (in the context of pathname
resolution with symbolic links followed) to a directory, then the cd utility
shall display an appropriate error message and no further steps shall be
taken.

ii. The preceding component, all <slash> characters separating the preceding
component from dot-dot, dot-dot, and all <slash> characters separating dot-
dot from the following component (if any) shall be deleted.

c. An implementation may further simplify curpath by removing any trailing <slash>
characters that are not also leading <slash> characters, replacing multiple non-
leading consecutive <slash> characters with a single <slash>, and replacing three
or more leading <slash> characters with a single <slash>. If, as a result of this
canonicalization, the curpath variable is null, no further steps shall be taken.

9. If curpath is longer than {PATH_MAX} bytes (including the terminating null) and the
directory operand was not longer than {PATH_MAX} bytes (including the terminating
null), then curpath shall be converted from an absolute pathname to an equivalent
relative pathname if possible. This conversion shall always be considered possible if
the value of PWD, with a trailing <slash> added if it does not already have one, is an
initial substring of curpath. Whether or not it is considered possible under other
circumstances is unspecified. Implementations may also apply this conversion if
curpath is not longer than {PATH_MAX} bytes or the directory operand was longer than
{PATH_MAX} bytes.

10. The cd utility shall then perform actions equivalent to the chdir() function called
with curpath as the path argument. If these actions fail for any reason, the cd
utility shall display an appropriate error message and the remainder of this step
shall not be executed. If the −P option is not in effect, the PWD environment variable
shall be set to the value that curpath had on entry to step 9 (i.e., before conversion
to a relative pathname). If the −P option is in effect, the PWD environment variable
shall be set to the string that would be output by pwd −P. 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, during the execution of the above steps, the PWD environment variable is set, the
OLDPWD environment variable shall also be set 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 POSIX.1‐2008, 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


Not used.

INPUT FILES


None.

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 POSIX.1‐2008, 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


Default.

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.

STDERR


The standard error shall be used only for diagnostic messages.

OUTPUT FILES


None.

EXTENDED DESCRIPTION


None.

EXIT STATUS


The following exit values shall be returned:

0 The directory was successfully changed.

>0 An error occurred.

CONSEQUENCES OF ERRORS


The working directory shall remain unchanged.

The following sections are informative.

APPLICATION USAGE


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.

EXAMPLES


The following template can be used to perform processing in the directory specified by
location and end up in the current working directory in use before the first cd command
was issued:

cd location
if [ $? -ne 0 ]
then
print error message
exit 1
fi
... do whatever is desired as long as the OLDPWD environment variable
is not modified
cd -

RATIONALE


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.

FUTURE DIRECTIONS


None.

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