File

Public Class Methods

atomic_write(file_name, temp_dir = Dir.tmpdir) 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
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:     yield temp_file
21:     temp_file.close
22: 
23:     begin
24:       # Get original file permissions
25:       old_stat = stat(file_name)
26:     rescue Errno::ENOENT
27:       # No old permissions, write a temp file to determine the defaults
28:       check_name = join(dirname(file_name), ".permissions_check.#{Thread.current.object_id}.#{Process.pid}.#{rand(1000000)}")
29:       open(check_name, "w") { }
30:       old_stat = stat(check_name)
31:       unlink(check_name)
32:     end
33: 
34:     # Overwrite original file with temp file
35:     FileUtils.mv(temp_file.path, file_name)
36: 
37:     # Set correct permissions on new file
38:     chown(old_stat.uid, old_stat.gid, file_name)
39:     chmod(old_stat.mode, file_name)
40:   end

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