Originální popis anglicky:
cd - change the working directory
Návod, kniha: POSIX Programmer's Manual
cd [-L | -P] [directory]
cd -
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).
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.
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:
which changes to the previous working directory and then writes its name.
Not used.
None.
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.
Default.
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:
Otherwise, there shall be no output.
The standard error shall be used only for diagnostic messages.
None.
None.
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.
None.
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:
In such a shell, the following commands would not necessarily produce equivalent
output for all directories:
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.
None.
Shell Execution Environment ,
pwd , the System Interfaces volume
of IEEE Std 1003.1-2001,
chdir()
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
.
