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Class Public methods

atomic_write(file_name, temp_dir = dirname(file_name))

Write to a file atomically. Useful for situations where you don’t want other processes or threads to see half-written files.

File.atomic_write('important.file') do |file|
  file.write('hello')
end

This method needs to create a temporary file. By default it will create it in the same directory as the destination file. If you don’t like this behavior you can provide a different directory but it must be on the same physical filesystem as the file you’re trying to write.

File.atomic_write('/data/something.important', '/data/tmp') do |file|
  file.write('hello')
end

Source: show | on GitHub 

# File activesupport/lib/active_support/core_ext/file/atomic.rb, line 26
def self.atomic_write(file_name, temp_dir = dirname(file_name))
  old_stat = begin
    File.stat(file_name)
  rescue SystemCallError
    nil
  end

  # Names can't be longer than 255B
  tmp_suffix = ".tmp.#{SecureRandom.hex}"
  tmp_name = ".#{basename(file_name).byteslice(0, 254 - tmp_suffix.bytesize)}#{tmp_suffix}"
  tmp_path = File.join(temp_dir, tmp_name)
  temp_file = open(tmp_path, RDWR | CREAT | EXCL | SHARE_DELETE | BINARY)
  temp_file.binmode

  if old_stat
    # Set correct permissions on new file
    begin
      temp_file.chown(old_stat.uid, old_stat.gid)
      # This operation will affect filesystem ACL's
      temp_file.chmod(old_stat.mode)
    rescue Errno::EPERM, Errno::EACCES
      # Changing file ownership failed, moving on.
    end
  end

  return_val = yield temp_file

  temp_file.close
  rename(temp_file.path, file_name)
  temp_file = nil

  return_val
ensure
  if temp_file
    temp_file.close rescue nil
    unlink(temp_file.path) rescue nil
  end
end