答案由Caleb Spare张贴在gonuts邮件列表中。

[...] It's not actually needed very often and [...] using os.Stat is easy enough for the cases where it is required. [...] For instance: if you are going to open the file, there's no reason to check whether it exists first. The file could disappear in between checking and opening, and anyway you'll need to check the os.Open error regardless. So you simply call os.IsNotExist(err) after you try to open the file, and deal with its non-existence there (if that requires special handling). [...] You don't need to check for the paths existing at all (and you shouldn't). os.MkdirAll works whether or not the paths already exist. (Also you need to check the error from that call.) Instead of using os.Create, you should use os.OpenFile(path, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0666) . That way you'll get an error if the file already exists. Also this doesn't have a race condition with something else making the file, unlike your version which checks for existence beforehand.

摘自:https://groups.google.com/forum/#!味精rl8ffhr8v4j / golang-nuts / Ayx-BMNdMFo / 4

其他答案忽略的是，给函数的路径实际上可能是一个目录。下面的函数确保，路径确实是一个文件。

func fileExists(filename string) bool {
    info, err := os.Stat(filename)
    if os.IsNotExist(err) {
        return false
    }
    return !info.IsDir()
}

另一件需要指出的事情是:这段代码仍然可能导致竞态条件，即在fileExists函数运行时，另一个线程或进程删除或创建指定的文件。

如果您担心这一点，可以在线程中使用锁，序列化对该函数的访问，或者在涉及多个应用程序时使用进程间信号量。如果涉及到其他应用程序，超出了您的控制范围，我想您就不走运了。

检查一个文件是否不存在，相当于Python的if not os.path.exists(filename):

if _, err := os.Stat("/path/to/whatever"); errors.Is(err, os.ErrNotExist) {
  // path/to/whatever does not exist
}

检查一个文件是否存在，相当于Python的if os.path.exists(filename):

编辑:根据最近的评论

if _, err := os.Stat("/path/to/whatever"); err == nil {
  // path/to/whatever exists

} else if errors.Is(err, os.ErrNotExist) {
  // path/to/whatever does *not* exist

} else {
  // Schrodinger: file may or may not exist. See err for details.

  // Therefore, do *NOT* use !os.IsNotExist(err) to test for file existence


}

首先要考虑的是，您很少只想检查一个文件是否存在。在大多数情况下，如果文件存在，您将尝试对它做一些事情。在Go中，每当你试图对一个不存在的文件执行一些操作时，结果应该是一个特定的错误(os.ErrNotExist)，最好的方法是检查返回的err值(例如在调用os.OpenFile(…)这样的函数时)是否为os.ErrNotExist。

这样做的推荐方法是:

file, err := os.OpenFile(...)
if os.IsNotExist(err) {
    // handle the case where the file doesn't exist
}

但是，由于添加了错误。在Go 1.13(2019年底发布)中，新的建议是使用错误。是:

file, err := os.OpenFile(...)
if errors.Is(err, os.ErrNotExist) {
    // handle the case where the file doesn't exist
}

通常最好避免使用os。在尝试对文件做一些事情之前，Stat检查文件是否存在，因为在对文件做一些事情之前，文件总是有可能被重命名、删除等。

然而，如果你接受这个警告，你真的，真的只是想检查一个文件是否存在，而不是继续对它做一些有用的事情(作为一个人为的例子，假设你正在编写一个毫无意义的CLI工具，告诉你一个文件是否存在，然后退出¯\_()_/¯)，那么推荐的方法是:

if _, err := os.Stat(filename); errors.Is(err, os.ErrNotExist) {
    // file does not exist
} else {
    // file exists
}

    _, err := os.Stat(file)
    if err == nil {
        log.Printf("file %s exists", file)
    } else if os.IsNotExist(err) {
        log.Printf("file %s not exists", file)
    } else {
        log.Printf("file %s stat error: %v", file, err)
    }

正如在其他回答中提到的，可以通过使用os.OpenFile的不同标志来构造所需的行为/错误。事实上，os。Create只是这样做的一个合理的默认值简写:

// Create creates or truncates the named file. If the file already exists,
// it is truncated. If the file does not exist, it is created with mode 0666
// (before umask). If successful, methods on the returned File can
// be used for I/O; the associated file descriptor has mode O_RDWR.
// If there is an error, it will be of type *PathError.
func Create(name string) (*File, error) {
    return OpenFile(name, O_RDWR|O_CREATE|O_TRUNC, 0666)
}

你应该自己结合这些标志来获得你感兴趣的行为:

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

根据您选择的内容，您将得到不同的错误。

下面是一个示例，它将截断一个现有文件，或者当文件存在时失败。

openOpts := os.O_RDWR|os.O_CREATE
if truncateWhenExists {
    openOpts |= os.O_TRUNC // file will be truncated
} else {
    openOpts |= os.O_EXCL  // file must not exist
}
f, err := os.OpenFile(filePath, openOpts, 0644)
// ... do stuff