Methods

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 code 
# File activesupport/lib/active_support/core_ext/file/atomic.rb, line 21
  def self.atomic_write(file_name, temp_dir = dirname(file_name))
    require "tempfile" unless defined?(Tempfile)

    Tempfile.open(".#{basename(file_name)}", temp_dir) do |temp_file|
      temp_file.binmode
      return_val = yield temp_file
      temp_file.close

      old_stat = if exist?(file_name)
        # Get original file permissions
        stat(file_name)
      else
        # If not possible, probe which are the default permissions in the
        # destination directory.
        probe_stat_in(dirname(file_name))
      end

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

      # Overwrite original file with temp file
      rename(temp_file.path, file_name)
      return_val
    end
  end
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