local: local [option] 名称[=值] ...
Define local variables.

    Create a local variable called NAME, and give it VALUE.  OPTION can
    be any option accepted by `declare'.

    Local variables can only be used within a function; they are visible
    only to the function where they are defined and its children.

    Exit Status:
    Returns success unless an invalid option is supplied, a variable
    assignment error occurs, or the shell is not executing a function.