没有cd命令的手册页

Question

Ubuntu Linux 15.10 - 我刚注意到没有手册页 cd

这看起来有点奇怪.

我试过了:

man cd

在cmd线,我回来了

No manual entry for cd

我试图找到文档

cd -

这对于在最后一个目录和当前目录之间翻转非常方便

和 cd --

这似乎是别名

cd ~

我在这里遗漏了一些非常明显的东西,或者手册页应该存在吗？

Answer 1

cd它不是一个命令,它内置在你的shell中.这是必要的,因为您当前的工作目录由PWD以pwd"print working directory"命令命名的环境变量控制.

子进程无法更改父进程的环境变量.因此,如果你的shell运行了/bin/cd哪个更改PWD它只会影响/bin/cd它运行的任何东西.它不会改变shell的PWD.

某些系统(如OS X和CentOS)会将cd手册页映射到builtin列出所有shell内置的手册页,并告诉您应该查看shell的手册页.

你可以检查你有壳echo $SHELL,它可能bash.

Answer 2

cd 是一个内置的shell命令.

您可以打开cdBash 的帮助页面

$ help cd

目前显示的是(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,它没有回答你的问题.还有就是文档,做不过来.

你可以用它来实现

$ man builtins

它打开了许多页面的帮助less,我的默认查看器.我可以通过按键找到cd的帮助/,然后键入cd,然后Enter按n两次让我到子串的第三个实例,帮助,其中显示:

   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.

-从最后寻找关于第七行的论点.

请注意,没有--参数 - 这似乎意味着它实际上忽略了它.