io - 标准输入输出（I/O）服务接口函数
- columns/0
- columns/1
- format/1
- format/2
- format/3
- fread/2
- fread/3
- fwrite/1
- fwrite/2
- fwrite/3
- get_chars/2
- get_chars/3
- get_line/1
- get_line/2
- getopts/0
- getopts/1
- nl/0
- nl/1
- parse_erl_exprs/1
- parse_erl_exprs/2
- parse_erl_exprs/3
- parse_erl_form/1
- parse_erl_form/2
- parse_erl_form/3
- put_chars/1
- put_chars/2
- read/1
- read/2
- read/3
- rows/0
- rows/1
- scan_erl_exprs/1
- scan_erl_exprs/2
- scan_erl_exprs/3
- scan_erl_form/1
- scan_erl_form/2
- scan_erl_form/3
- setopts/1
- setopts/2
- write/1
- write/2