说明
mixed
readline_info ( [string varname [, string newvalue]] )
Gets or sets various internal readline variables.
返回值
If called with no parameters, this function returns an array of
values for all the setting readline uses. The elements will
be indexed by the following values: done, end, erase_empty_line,
library_version, line_buffer, mark, pending_input, point, prompt,
readline_name, and terminal_name.
If called with one or two parameters, the old value is returned.