Methods
Public Instance methods
atomic_write(file_name, temp_dir = Dir.tmpdir) {|temp_file| ...}

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 |f|
    file.write("hello")
  end

[ show source ]

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