Linux命令:builtin

builtin [shell-builtin [arg ...]]

说明：

明确告诉bash执行的是内建命令，而不是和内建命令同名的函数。这实际就是bash容许用户自定义和builtin命令同名的函数，但是执行时，要区分到底执行的是哪个，默认就是函数啦，前面带上builtin就是执行bash自己的内建命令啦。

如果不是builtin命令，而用builtin执行，则返回非0。或者builtin命令的退出码。

Bash允许用户定义和builtin同名的函数，这有点像c++里的重载，用户自定义函数override内部命令了。

help builtin

 1 builtin: builtin [shell-builtin [arg ...]]
 2     Execute shell builtins.
 3 
 4     Execute SHELL-BUILTIN with arguments ARGs without performing command
 5     lookup.  This is useful when you wish to reimplement a shell builtin
 6     as a shell function, but need to execute the builtin within the function.
 7 
 8     Exit Status:
 9     Returns the exit status of SHELL-BUILTIN, or false if SHELL-BUILTIN is
10     not a shell builtin..