#Bash 的 cd 命令
cd [-L|-P] [DIRECTORY]
功能
切换工作目录。
类型
Bash 内置命令。
参数
OPTION选项：-L- 逻辑路径；在跟踪符号链接之前解析..（默认）-P- 物理路径；在跟踪符号链接之后解析..
DIRECTORY- 要切换到的目录路径；省略表示切换到用户目录，-表示切换到上次的工作目录
#示例
基本示例
$ pwd # 查看当前路径
/home/user/primers
$ cd bash # 相对路径
$ pwd
/home/user/primers/bash
$ cd - # 切换回之前的目录
$ pwd
/home/user/primers
$ cd /etc # 绝对路径
$ pwd
/etc
符号链接
$ pwd # 查看当前路径
/home/user/primers
$ ln -s /usr/lib lib # 创建符号链接
$ cd lib # 进入 lib
$ pwd
/home/user/primers/bash/lib
$ cd .. # 返回上级目录
$ cd -P lib # 进入 lib，跟踪符号链接
$ pwd
/usr/lib
#相关命令
#推荐阅读
#手册
CD(1P) POSIX Programmer's Manual CD(1P)
PROLOG top
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
NAME top
cd — change the working directory
SYNOPSIS top
cd [-L|-P] [directory]
cd -
DESCRIPTION top
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 top
The cd utility shall conform to the Base Definitions volume of
POSIX.1‐2017, 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 top
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-minus> 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 top
Not used.
INPUT FILES top
None.
ENVIRONMENT VARIABLES top
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.1‐2017, 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 top
Default.
STDOUT top
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 top
The standard error shall be used only for diagnostic messages.
OUTPUT FILES top
None.
EXTENDED DESCRIPTION top
None.
EXIT STATUS top
The following exit values shall be returned:
0 The directory was successfully changed.
>0 An error occurred.
CONSEQUENCES OF ERRORS top
The working directory shall remain unchanged.
The following sections are informative.
APPLICATION USAGE top
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 top
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 top
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 top
None.
SEE ALSO top
Section 2.12, Shell Execution Environment, pwd(1p)
The Base Definitions volume of POSIX.1‐2017, Chapter 8,
Environment Variables, Section 12.2, Utility Syntax Guidelines
The System Interfaces volume of POSIX.1‐2017, chdir(3p)
COPYRIGHT top
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 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 .
Any typographical or formatting errors that appear in this page
are most likely to have been introduced during the conversion of
the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 CD(1P)