func OpenFile(name string, flag int, perm FileMode) (*File, error) 

// Flags to OpenFile wrapping those of the underlying system. Not all
// flags may be implemented on a given system.
const (// Exactly one of O_RDONLY, O_WRONLY, or O_RDWR must be specified.// 只读模式O_RDONLY int = syscall.O_RDONLY // open the file read-only.// 只写模式O_WRONLY int = syscall.O_WRONLY // open the file write-only.// 可读可写O_RDWR   int = syscall.O_RDWR   // open the file read-write.// The remaining values may be or'ed in to control behavior.// 追加内容O_APPEND int = syscall.O_APPEND // append data to the file when writing.// 创建文件，如果文件不存在O_CREATE int = syscall.O_CREAT  // create a new file if none exists.// 与创建文件一同使用，文件必须存在O_EXCL   int = syscall.O_EXCL   // used with O_CREATE, file must not exist.// 打开一个同步的文件流O_SYNC   int = syscall.O_SYNC   // open for synchronous I/O.// 如果可能，打开时缩短文件O_TRUNC  int = syscall.O_TRUNC  // truncate regular writable file when opened.
)

// The defined file mode bits are the most significant bits of the FileMode.
// The nine least-significant bits are the standard Unix rwxrwxrwx permissions.
// The values of these bits should be considered part of the public API and
// may be used in wire protocols or disk representations: they must not be
// changed, although new bits might be added.
const (// The single letters are the abbreviations// used by the String method's formatting.// 文件夹模式ModeDir        FileMode = 1 << (32 - 1 - iota) // d: is a directory// 追加模式ModeAppend                                     // a: append-only// 单独使用ModeExclusive                                  // l: exclusive use// 临时文件ModeTemporary                                  // T: temporary file; Plan 9 only// 象征性的关联ModeSymlink                                    // L: symbolic link// 设备文件ModeDevice                                     // D: device file// 命名管道ModeNamedPipe                                  // p: named pipe (FIFO)// Unix 主机 socketModeSocket                                     // S: Unix domain socket// 设置uidModeSetuid                                     // u: setuid// 设置gidModeSetgid                                     // g: setgid// UNIX 字符串设备，当设备模式是设置unixModeCharDevice                                 // c: Unix character device, when ModeDevice is set// 粘性的ModeSticky                                     // t: sticky// 非常规文件；对该文件一无所知ModeIrregular                                  // ?: non-regular file; nothing else is known about this file// bit位遮盖，不变的文件设置为none// Mask for the type bits. For regular files, none will be set.ModeType = ModeDir | ModeSymlink | ModeNamedPipe | ModeSocket | ModeDevice | ModeCharDevice | ModeIrregular// 权限位ModePerm FileMode = 0777 // Unix permission bits
)

package mainimport ("os"
)
func main() {fname := "/tmp/t.txt"f, err := os.OpenFile(fname, os.O_CREATE|os.O_RDWR|os.O_APPEND, os.ModeAppend|os.ModePerm)if err != nil {fmt.Println(err)}f.WriteString("test")f.Close()
}

os.MkdirAll(dname,os.ModeDir|os.ModePerm)