golang

const (
	O_RDONLY = os.O_RDONLY // open the file read-only.
	O_WRONLY = os.O_WRONLY // open the file write-only.
	O_RDWR   = os.O_RDWR   // open the file read-write.
	// The remaining values may be or'ed in to control behavior.
	O_APPEND = os.O_APPEND // append data to the file when writing.
	O_CREATE = os.O_CREATE // create a new file if none exists.
	O_EXCL   = os.O_EXCL   // used with O_CREATE, file must not exist.
	O_SYNC   = os.O_SYNC   // open for synchronous I/O.
	O_TRUNC  = os.O_TRUNC  // truncate regular writable file when opened.
)