一天一条Linux指令-type

用途说明

type命令用来显示指定命令的类型。一个命令的类型可以是如下之一
alias 别名
keyword 关键字，Shell保留字
function 函数，Shell函数
builtin 内建命令，Shell内建命令
file 文件，磁盘文件，外部命令
unfound 没有找到

它是Linux系统的一种自省机制，知道了是那种类型，我们就可以针对性的获取帮助。比如内建命令可以用help命令来获取帮助，外部命令用man或者info来获取帮助。

常用参数

type命令的基本使用方式就是直接跟上命令名字。

type -a可以显示所有可能的类型，比如有些命令如pwd是shell内建命令，也可以是外部命令。

type -p只返回外部命令的信息，相当于which命令。

type -f只返回shell函数的信息。

type -t 只返回指定类型的信息。

使用示例

示例一 type自己是什么类型的命令

[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 ~]#

示例二 常见命令的类型

[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 ~]#