沒有 cd 命令的手冊頁

Question

Ubuntu Linux 15.10 - 我剛剛注意到cd沒有手冊頁

這似乎有點奇怪。

我試過：

man cd

在 cmd 行，我回來了

No manual entry for cd

我試圖找到有關的文檔

cd -

這對於在最后一個目錄和當前目錄之間翻轉非常方便

和cd --

這似乎是一個別名

cd ~

我在這里遺漏了一些非常明顯的東西，還是應該提供手冊頁？

Answer 1

cd不是命令，它內置於您的 shell 中。 這是必要的，因為您當前的工作目錄由以pwd或“打印工作目錄”命令命名的PWD環境變量控制。

子進程不能更改父進程的環境變量。 因此，如果您的 shell 運行/bin/cd更改了PWD它只會影響/bin/cd及其運行的任何內容。 它不會改變外殼的PWD 。

某些系統，如 OS X 和 CentOS，將cd手冊頁映射到builtin ，其中列出了所有 shell 內置程序，並讓您知道應該查看 shell 的手冊頁。

您可以使用echo $SHELL檢查您擁有的echo $SHELL ，它可能是bash 。

Answer 2

cd是一個內置的 shell 命令。

$ type cd
cd is a shell builtin

您可以在 Bash 上打開cd的幫助頁面

$ help cd

目前顯示（Ubuntu 16.04）：

$ help cd
cd: cd [-L|[-P [-e]] [-@]] [dir]
    Change the shell working directory.

    Change the current directory to DIR.  The default DIR is the value of the
    HOME shell variable.

    The variable CDPATH defines the search path for the directory containing
    DIR.  Alternative directory names in CDPATH are separated by a colon (:).
    A null directory name is the same as the current directory.  If DIR begins
    with a slash (/), then CDPATH is not used.

    If the directory is not found, and the shell option `cdable_vars' is set,
    the word is assumed to be  a variable name.  If that variable has a value,
    its value is used for DIR.

    Options:
        -L  force symbolic links to be followed: resolve symbolic links in
        DIR after processing instances of `..'
        -P  use the physical directory structure without following symbolic
        links: resolve symbolic links in DIR before processing instances
        of `..'
        -e  if the -P option is supplied, and the current working directory
        cannot be determined successfully, exit with a non-zero status
        -@  on systems that support it, present a file with extended attributes
            as a directory containing the file attributes

    The default is to follow symbolic links, as if `-L' were specified.
    `..' is processed by removing the immediately previous pathname component
    back to a slash or the beginning of DIR.

    Exit Status:
    Returns 0 if the directory is changed, and if $PWD is set successfully when
    -P is used; non-zero otherwise.

不幸的是，它沒有回答您的問題。 有文檔，做不過來。

你可以用

$ man builtins

它使用我的默認查看器less打開許多幫助頁面。 我可以通過按/鍵找到 cd 的幫助，然后輸入cd ，然后Enter ，然后按兩次n可以找到子字符串的第三個實例，幫助內容如下：

   cd [-L|[-P [-e]] [-@]] [dir]
          Change  the  current  directory to dir.  if dir is not supplied,
          the value of the HOME shell variable is the default.  Any  addi‐
          tional arguments following dir are ignored.  The variable CDPATH
          defines the search path for the directory containing  dir:  each
          directory  name  in  CDPATH  is  searched  for dir.  Alternative
          directory names in CDPATH are separated by a colon (:).  A  null
          directory  name  in CDPATH is the same as the current directory,
          i.e., ``.''.  If dir begins with a slash (/), then CDPATH is not
          used.  The  -P  option  causes  cd to use the physical directory
          structure by resolving symbolic links while traversing  dir  and
          before processing instances of .. in dir (see also the -P option
          to the set builtin command); the -L option forces symbolic links
          to  be followed by resolving the link after processing instances
          of .. in dir.  If .. appears in dir, it is processed by removing
          the  immediately previous pathname component from dir, back to a
          slash or the beginning of dir.  If the  -e  option  is  supplied
          with  -P,  and  the current working directory cannot be success‐
          fully determined after a successful directory  change,  cd  will
          return  an unsuccessful status.  On systems that support it, the
          -@ option presents the extended  attributes  associated  with  a
          file  as  a directory.  An argument of - is converted to $OLDPWD
          before the directory change is attempted.  If a non-empty direc‐
          tory  name  from  CDPATH is used, or if - is the first argument,
          and the directory change is successful, the absolute pathname of
          the  new  working  directory  is written to the standard output.
          The return value is  true  if  the  directory  was  successfully
          changed; false otherwise.

尋找關於從末尾開始的第七行的-參數：

在嘗試更改目錄之前， -的參數被轉換為$OLDPWD 。

請注意，沒有--參數 - 這似乎意味着它實際上忽略了它。

Answer 3

bash 手冊頁的相關摘錄，涵蓋了cd -使用cd -

       cd [-L|[-P [-e]] [-@]] [dir]
              Change the current directory to dir. 
              ...

              An argument of  -
              is  converted to $OLDPWD before the directory change is attempted.  If a non-
              empty directory name from CDPATH is used, or if - is the first argument,  and
              the  directory change is successful, the absolute pathname of the new working
              directory is written to the standard output.  The return value is true if the
              directory was successfully changed; false otherwise.