在脚本中type可用于检查命令或函数是否存在，存在返回0，表示成功；不存在返回正值，表示不成功。
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$ type foo >/dev/null 2>&1 || { echo >&2 "I require foo but it's not installed. Aborting."; exit 1; } |
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
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[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
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[root@new55 ~]# type -a cd cd is a shell builtin[root@new55 ~]# type -a pwd pwd is a shell builtinpwd is /bin/pwd[root@new55 ~]# type -a time time is a shell keywordtime 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 builtinecho 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 |
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原文链接：https://www.cnblogs.com/embedded-linux/p/6206052.html
