Methods
A
Class Public methods
atomic_write(file_name, temp_dir = Dir.tmpdir)

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

Source: show | on GitHub 

    # File activesupport/lib/active_support/core_ext/file/atomic.rb, line 15
15:   def self.atomic_write(file_name, temp_dir = Dir.tmpdir)
16:     require 'tempfile' unless defined?(Tempfile)
17:     require 'fileutils' unless defined?(FileUtils)
18: 
19:     temp_file = Tempfile.new(basename(file_name), temp_dir)
20:     temp_file.binmode
21:     yield temp_file
22:     temp_file.close
23: 
24:     begin
25:       # Get original file permissions
26:       old_stat = stat(file_name)
27:     rescue Errno::ENOENT
28:       # No old permissions, write a temp file to determine the defaults
29:       check_name = join(dirname(file_name), ".permissions_check.#{Thread.current.object_id}.#{Process.pid}.#{rand(1000000)}")
30:       open(check_name, "w") { }
31:       old_stat = stat(check_name)
32:       unlink(check_name)
33:     end
34: 
35:     # Overwrite original file with temp file
36:     FileUtils.mv(temp_file.path, file_name)
37: 
38:     # Set correct permissions on new file
39:     chown(old_stat.uid, old_stat.gid, file_name)
40:     chmod(old_stat.mode, file_name)
41:   end