File Ports

Two special procedures work on file ports:

• (flush-output [port]) forces all buffered data in the given file output port to be physically written. Buffered data is automatically flushed after each newline. The initial standard output and error ports are automatically flushed when read, read-line, read-string, or read-string! are performed on the initial standard input port. When called on a non-file port, flush-output takes no action. If port is omitted, then the current output port is flushed.
• (file-position port) returns the current read/write position of the file port port, and (file-position port pos) sets the read/write position to pos. Calling file-position without a position on a non-file input port returns the number of characters that have been read from that port. The file-position procedure can return the current position for any import or export port, but calling file-position with a position and a non-file port raises the exn:application-file-position exception.