12. 命令
• Shell关键字 alias别名
!
• 内建命令 function函数
!
• 外部命令
bash-3.2$ type if
if is a shell keyword
bash-3.2$ type type
type is a shell builtin
bash-3.2$ type grep
grep is /usr/bin/grep
bash-3.2$ type ll
ll is an alias for ls -l
bash-3.2$ type take
take is a shell function