linux?type命令用法实战教程
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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。
$ 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
[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
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