How to check if a file exists in Go?

问题

Go's standard library does not have a function solely intended to check if a file exists or not (like Python's os.path.exists). What is the idiomatic way to do it?

回答1:

To check if a file doesn't exist, equivalent to Python's if not os.path.exists(filename):

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

To check if a file exists, equivalent to Python's if os.path.exists(filename):

Edited: per recent comments

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

} else if os.IsNotExist(err) {
  // 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


}

回答2:

Answer by Caleb Spare posted in gonuts mailing list.

[...] 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.

Taken from: https://groups.google.com/forum/#!msg/golang-nuts/Ayx-BMNdMFo/4rL8FFHr8v4J

回答3:

You should use the os.Stat() and os.IsNotExist() functions as in the following example:

// Exists reports whether the named file or directory exists.
func Exists(name string) bool {
    if _, err := os.Stat(name); err != nil {
        if os.IsNotExist(err) {
            return false
        }
    }
    return true
}

The example is extracted from here.

回答4:

The example by user11617 is incorrect; it will report that the file exists even in cases where it does not, but there was an error of some other sort.

The signature should be Exists(string) (bool, error). And then, as it happens, the call sites are no better.

The code he wrote would better as:

func Exists(name string) bool {
    _, err := os.Stat(name)
    return !os.IsNotExist(err)
}

But I suggest this instead:

func Exists(name string) (bool, error) {
  _, err := os.Stat(name)
  if os.IsNotExist(err) {
    return false, nil
  }
  return err != nil, err
}

回答5:

    _, 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)
    }

回答6:

The function example:

func file_is_exists(f string) bool {
    _, err := os.Stat(f)
    if os.IsNotExist(err) {
        return false
    }
    return err == nil
}

回答7:

Let's look at few aspects first, both the function provided by os package of golang are not utilities but error checkers, what do I mean by that is they are just a wrapper to handle errors on cross platform.

So basically if os.Stat if this function doesn't give any error that means the file is existing if it does you need to check what kind of error it is, here comes the use of these two function os.IsNotExist and os.IsExist.

This can be understood as the Stat of the file throwing error because it doesn't exists or is it throwing error because it exist and there is some problem with it.

The parameter that these functions take is of type error, although you might be able to pass nil to it but it wouldn't make sense.

This also points to the fact that IsExist is not same as !IsNotExist, they are way two different things.

So now if you want to know if a given file exist in go, I would prefer the best way is:

if _, err := os.Stat(path/to/file); !os.IsNotExist(err){
   //TODO
}

回答8:

What other answers missed, is that the path given to the function could actually be a directory. Following function makes sure, that the path is really a file.

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

Another thing to point out: This code could still lead to a race condition, where another thread or process deletes or creates the specified file, while the fileExists function is running.

If you're worried about this, use a lock in your threads, serialize the access to this function or use an inter-process semaphore if multiple applications are involved. If other applications are involved, outside of your control, you're out of luck, I guess.

来源：https://stackoverflow.com/questions/12518876/how-to-check-if-a-file-exists-in-go

标签

file

standard-library