# class File

### Public Class Methods

atomic_write(file_name, temp_dir = Dir.tmpdir) { |temp_file| ... } click to toggle source

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

If your temp directory is not on the same filesystem as the file you’re trying to write, you can provide a different temporary directory.

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

    # File lib/active_support/core_ext/file/atomic.rb, line 15
    def self.atomic_write(file_name, temp_dir = Dir.tmpdir)
      require 'tempfile' unless defined?(Tempfile)
      require 'fileutils' unless defined?(FileUtils)

      temp_file = Tempfile.new(basename(file_name), temp_dir)
      yield temp_file
      temp_file.close

      begin
        # Get original file permissions
        old_stat = stat(file_name)
      rescue Errno::ENOENT
        # No old permissions, write a temp file to determine the defaults
        check_name = join(dirname(file_name), ".permissions_check.#{Thread.current.object_id}.#{Process.pid}.#{rand(1000000)}")
        open(check_name, "w") { }
        old_stat = stat(check_name)
        unlink(check_name)
      end

      # Overwrite original file with temp file
      FileUtils.mv(temp_file.path, file_name)

      # Set correct permissions on new file
      chown(old_stat.uid, old_stat.gid, file_name)
      chmod(old_stat.mode, file_name)
    end