Linux命令之type - 显示命令的类型

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 ~]#

问题思考

相关资料

【1】Blue_Stone's OpenWorld Linux中的type命令
【2】山海经 Linux中的type命令

【3】鸟哥的私房菜 Bash shell 的內建命令： type
【4】阮一峰的网络日志 Linux的五个查找命令

原文地址：http://codingstandards.iteye.com/blog/831504