class File - activesupport-4.2.4 Documentation

# 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 17
    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)
      temp_file.binmode
      yield temp_file
      temp_file.close

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

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

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