[root@VM_0_14_centos ~]# whereis ls ? ? ?/////////查找ls，存在執(zhí)行文件位置以及幫助文件位置

ls: /usr/bin/ls /usr/share/man/man1/ls.1.gz

[root@VM_0_14_centos ~]# whereis cd ? ///////查找 cd，一樣的結果

cd: /usr/bin/cd /usr/share/man/man1/cd.1.gz

[root@VM_0_14_centos ~]# man cd

[6]+ ?Stopped ? ? ? ? ? ? ? ? man cd

[root@VM_0_14_centos ~]# man cd?

[7]+ ?Stopped ? ? ? ? ? ? ? ? man cd

[root@VM_0_14_centos ~]# help cd ? ///////help cd，可以查找出來

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

? ? ? ? -P use the physical directory structure without following symbolic

? ? links

? ? ? ? -e if the -P option is supplied, and the current working directory

? ? cannot be determined successfully, exit with a non-zero status

? ??

? ? The default is to follow symbolic links, as if `-L' were specified.

? ??

? ? Exit Status:

? ? Returns 0 if the directory is changed, and if $PWD is set successfully when

? ? -P is used; non-zero otherwise.

[root@VM_0_14_centos ~]# help ls ? //////help ls，無結果

-bash: help: no help topics match `ls'. ?Try `help help' or `man -k ls' or `info ls'.

疑問：為什么help cd有結果，whereis cd的結果于whereis ls 的結果是一樣的