type命令用來顯示指定命令的型別。乙個命令的型別可以是如下之一
它是linux系統的一種自省機制，知道了是那種型別，我們就可以針對性的獲取幫助。比如內建命令可以用help命令來獲取幫助，外部命令用man或者info來獲取幫助。
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型別，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函式的資訊。
type -t 只返回指定型別的資訊。
[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 ~]#
[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 ~]#
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