Ubuntu Manpage: cd - change the working directory

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

       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 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

       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

       None.

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.

COPYRIGHT

       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2003 Edition, Standard for Information Technology  --  Portable  Operating  System
       Interface  (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by
       the Institute of Electrical and Electronics Engineers, Inc and  The  Open  Group.  In  the
       event  of  any  discrepancy  between this version and the original IEEE and The Open Group
       Standard, the original IEEE and The Open Group  Standard  is  the  referee  document.  The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .