Linux命令之type顯示命令的類型

type命令用途說明

type命令用來顯示指定命令的類型。一個命令的類型可以是如下之一

    alias 別名
    keyword 關鍵字，Shell保留字
    function 函數，Shell函數
    builtin 內建命令，Shell內建命令
    file 檔案，磁碟檔案，外部命令
    unfound 沒有找到

它是Linux系統的一種自省機制，知道了是那種類型，我們就可以針對性的擷取協助。比如內建命令可以用help命令來擷取協助，外部命令用man或者info來擷取協助。
常用參數WIIU創意之路：體感手柄與玩遊戲的改變

type命令的基本使用方式就是直接跟上命令名字。

type -a可以顯示所有可能的類型，比如有些命令如pwd是shell內建命令，也可以是外部命令。

type -p只返回外部命令的資訊，相當於which命令。

type -f只返回shell函數的資訊。

type -t 只返回指定類型的資訊。
使用樣本
樣本一 type自己是什麼類型的命令

[root@new55 ~]# type -a type
type is a shell builtin
[root@new55 ~]# help type
type: type [-afptP] name [name ...]
    For each NAME, indicate how it would be interpreted if used as a
    command name.
   
    If the -t option is used, `type' outputs a single word which is one of
    `alias', `keyword', `function', `builtin', `file' or `', if NAME is an
    alias, shell reserved word, shell function, shell builtin, disk file,
    or unfound, respectively.
   
    If the -p flag is used, `type' either returns the name of the disk
    file that would be executed, or nothing if `type -t NAME' would not
    return `file'.
   
    If the -a flag is used, `type' displays all of the places that contain
    an executable named `file'.  This includes aliases, builtins, and
    functions, if and only if the -p flag is not also used.
   
    The -f flag suppresses shell function lookup.
   
    The -P flag forces a PATH search for each NAME, even if it is an alias,
    builtin, or function, and returns the name of the disk file that would
    be executed.
typeset: typeset [-afFirtx] [-p] name[=value] ...
    Obsolete.  See `declare'.
[root@new55 ~]#
樣本二 常見命令的類型

[root@new55 ~]# type -a cd
cd is a shell builtin
[root@new55 ~]# type -a pwd
pwd is a shell builtin
pwd is /bin/pwd
[root@new55 ~]# type -a time
time is a shell keyword
time is /usr/bin/time
[root@new55 ~]# type -a date
date is /bin/date
[root@new55 ~]# type -a which
which is aliased to `alias | /usr/bin/which --tty-only --read-alias --show-dot --show-tilde'
which is /usr/bin/which
[root@new55 ~]# type -a whereis
whereis is /usr/bin/whereis
[root@new55 ~]# type -a whatis
whatis is /usr/bin/whatis
[root@new55 ~]# type -a function
function is a shell keyword
[root@new55 ~]# type -a ls
ls is aliased to `ls --color=tty'
ls is /bin/ls
[root@new55 ~]# type -a ll
ll is aliased to `ls -l --color=tty'
[root@new55 ~]# type -a echo
echo is a shell builtin
echo is /bin/echo
[root@new55 ~]# type -a bulitin
-bash: type: bulitin: not found
[root@new55 ~]# type -a builtin
builtin is a shell builtin
[root@new55 ~]# type -a keyword
-bash: type: keyword: not found
[root@new55 ~]# type -a command
command is a shell builtin
[root@new55 ~]# type -a alias
alias is a shell builtin
[root@new55 ~]# type -a grep
grep is /bin/grep
[root@new55 ~]#