Create an empty text file

Question

I've been reading and googling all over but I can't seem to find this simple answer.

I have a function that reads a file, but if the files doesn't exists it panics. What I want to do is a function that before reading, checks if the files exists, and if not, it creates an empty file. Here is what I have.

func exists(path string) (bool, error) {
    _, err := os.Stat(path)
    if err == nil {
        return true, nil
    }
    if os.IsNotExist(err) {
        return false, nil
    }
    return true, err
}

Solution 1

Don't try to check the existence first, since you then have a race if the file is created at the same time. You can open the file with the O_CREATE flag to create it if it doesn't exist:

os.OpenFile(name, os.O_RDONLY|os.O_CREATE, 0666)

Solution 2

Just trying to improve the excellent accepted answer.

It's a good idea to check for errors and to Close() the opened file, since file descriptors are a limited resource. You can run out of file descriptors much sooner than a GC runs, and on Windows you can run into file sharing violations.

func TouchFile(name string) error {
    file, err := os.OpenFile(name, os.O_RDONLY|os.O_CREATE, 0644)
    if err != nil {
        return err
    }
    return file.Close()
}

Comments

[Emi]

Thanks for the quick reply, but how can I set flags to ioutil.ReadFile(fileName) ?

[nussjustin]

@CoppolaEmilio You can't pass flags to ioutil.ReadFile, but you could just use os.OpenFile with ioutil.ReadAll

[JimB]

@CoppolaEmilio: you don't. ioutil.ReadFile is just a convenience function to call os.Open and iotuil.ReadAll. If you need more control, you create your own similar function.

[AndreKR]

Doesn't this leak a file descriptor?

[AndreKR]

Ah, never mind, according to stackoverflow.com/a/8595507/476074 they are closed automatically.

[JimB]

@AndreKR: If you're worried about "leaking" file descriptors, you can't depend on the finalizer because finalizers are never guaranteed to run, but you should be closing the file anyway. Using os.O_CREATE to open a file and create it if it doesn't exist has nothing to do with making sure you call "Close"

[AndreKR]

Seems you are right, if there's no memory pressure it might never be GC'd. In that case I think the answer to "how to create an empty file" should include the call to Close().

[Ace.C]

Can this be used to create directories?