Question

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?

Answer 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"); errors.Is(err, os.ErrNotExist) {
  // path/to/whatever does not exist
}

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

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


}