###9. I/O introduction ####9.1 Streams
####9.2 Using the File Class
文件读取
mode = "r+"
file = File.open("xxx",mode)
文件的读取模式mode有如下可选
Mode | Meaning
-----+--------------------------------------------------------
"r" | Read-only, starts at beginning of file (default mode).
-----+--------------------------------------------------------
"r+" | Read-write, starts at beginning of file.
-----+--------------------------------------------------------
"w" | Write-only, truncates existing file
| to zero length or creates a new file for writing.
-----+--------------------------------------------------------
"w+" | Read-write, truncates existing file to zero length
| or creates a new file for reading and writing.
-----+--------------------------------------------------------
"a" | Write-only, starts at end of file if file exists,
| otherwise creates a new file for writing.
-----+--------------------------------------------------------
"a+" | Read-write, starts at end of file if file exists,
| otherwise creates a new file for reading and
| writing.
-----+--------------------------------------------------------
"b" | Binary file mode (may appear with
| any of the key letters listed above).
| Suppresses EOL <-> CRLF conversion on Windows. And
| sets external encoding to ASCII-8BIT unless explicitly
| specified.
-----+--------------------------------------------------------
"t" | Text file mode (may appear with
| any of the key letters listed above except "b").
