1. 可執行程式

   [

   [email protected] ~]# type nexus

   nexus is /usr/bin/nexus

2. 內建shell

   [[email protected] ~]# type cd

   cd is a shell builtin

3. 命令別名

   [[email protected] ~]# type cp

   cp is aliased to `cp -i'

[[email protected] ~]# which ls

alias ls='ls --color=auto'

         /usr/bin/ls

[[email protected] ~]# which cd

/usr/bin/cd

[[email protected] ~]# which nexus

/usr/bin/nexus

[[email protected] ~]# which cp

alias cp='cp -i'

         /usr/bin/cp

[[email protected] ~]#

1. help在前面：
   1. 語法：help common
   2. 舉例：

      [[email protected] ~]# help cd

      cd: cd [-L|[-P [-e]]] [dir]  [ ]表示可選選項，| 表示互斥選項，也就是要麼-L，要麼-P，兩種不能同時出現

          Change the shell working directory.

        

         

          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

2. help在後面：
   1. 語法： common --help
   2. 舉例：

      [[email protected] ~]# cd --help

      -bash: cd: --: invalid option  說明cd 命令不支援後置help，只支援前置help

      cd: usage: cd [-L|[-P [-e]]] [dir]

      [[email protected] ~]# mkdir –help  mkdir後置help

      Usage: mkdir [OPTION]... DIRECTORY...

      Create the DIRECTORY(ies), if they do not already exist.

      Mandatory arguments to long options are mandatory for short options too.

        -m, --mode=MODE   set file mode (as in chmod), not a=rwx - umask

        -p, --parents     no error if existing, make parent directories as needed

        -v, --verbose     print a message for each created directory

        -Z                   set SELinux security context of each created directory

                               to the default type

            --context[=CTX]  like -Z, or if CTX is specified then set the SELinux

                               or SMACK security context to CTX

            --help     display this help and exit

            --version  output version information and exit

 [[email protected] ~]# man cd

 is searched if no file is found in PATH.  If the sourcepath option to the

              shopt builtin command is turned off, the PATH is not  searched.   If  any

              arguments  are supplied, they become the positional parameters when file‐

              name is executed.  Otherwise the  positional  parameters  are  unchanged.

 Manual page cd(1) line 1/1489 2% (press h for help or q to quit)  1/1489:1表示當前頁 1489表示總的頁手

[[email protected] wys_bak]# apropos reset

clearerr (3)         - check and reset stream status

feof (3)             - check and reset stream status

ferror (3)           - check and reset stream status

fileno (3)           - check and reset stream status

[[email protected] wys_bak]# man 3 fileno

clearerr, feof, ferror, fileno - check and reset stream status

[[email protected] wys_bak]# whatis mkdir

mkdir (1)            - make directories

mkdir (1p)           - make directories

mkdir (2)            - create a directory

mkdir (3p)           - make a directory

[[email protected] wys_bak]# man 3 fileno

clearerr, feof, ferror, fileno - check and reset stream status
 

[[email protected] wys_bak]# alias

alias cp='cp -i'

alias egrep='egrep --color=auto'

alias fgrep='fgrep --color=auto'

alias grep='grep --color=auto'

alias l.='ls -d .* --color=auto'

alias ll='ls -l --color=auto'

alias ls='ls --color=auto'

alias mv='mv -i' 預設提示原來在這裡設定了

alias rm='rm -i' 預設提示原來在這裡設定了

alias which='alias | /usr/bin/which --tty-only --read-alias --show-dot --show-tilde'

[[email protected] wys_bak]# alias nexus_home='cd /home/nexus;ls;cd -' 定義別名

[[email protected] wys_bak]# nexus_home 使用命令別名

nexus  nexus-2.14.9-01  sonatype-work

/root/wys_bak

[[email protected] wys_bak]#

1. 定義好別名後可以在當前視窗的任何目錄執行
2. 如果當前視窗關閉後該命令別名就會失效，後續會介紹如何保持視窗永生效

[[email protected] wys_bak]# unalias nexus_home

[[email protected] wys_bak]# nexus_home

-bash: nexus_home: command not found