Class Better::Tempfile

  1. lib/better/tempfile.rb
Parent: DelegateClass(File)

A utility class for managing temporary files. When you create a Tempfile object, it will create a temporary file with a unique filename. A Tempfile objects behaves just like a File object, and you can perform all the usual file operations on it: reading data, writing data, changing its permissions, etc. So although this class does not explicitly document all instance methods supported by File, you can in fact call any File instance method on a Tempfile object.

Comparison to Ruby’s bundled version

  • Much better documentation.
  • Is unit tested.
  • Ruby 1.8’s version can generate “weird” path names that can confuse certain command line tools such as Curl. Better::Tempfile is based on Ruby 1.9’s version and generates saner filenames.
  • Ruby 1.8’s version has a bug which makes unlink-before-close (as described below) unusable: it raises an an exception when close is called if the tempfile was unlinked before.
  • Ruby 1.9.1’s version closes the file when unlink is called. This makes unlink-before-close unusable.
  • Ruby’s bundled version deletes the temporary file in its finalizer, even when unlink was called before. As a result it may potentially delete other Ruby processes’ temp files when it’s not supposed to.

Better::Tempfile is based on Ruby 1.9.2’s version (SVN 24594).


require 'better/tempfile'

file ='foo')
file.path      # => A unique filename in the OS's temp directory,
               #    e.g.: "/tmp/foo.24722.0"
               #    This filename contains 'foo' in its basename.
file.write("hello world")
file.rewind      # => "hello world"
file.unlink    # deletes the temp file

Good practices

Explicit close

When a Tempfile object is garbage collected, or when the Ruby interpreter exits, its associated temporary file is automatically deleted. This means that’s it’s unnecessary to explicitly delete a Tempfile after use, though it’s good practice to do so: not explicitly deleting unused Tempfiles can potentially leave behind large amounts of tempfiles on the filesystem until they’re garbage collected. The existance of these temp files can make it harder to determine a new Tempfile filename.

Therefore, one should always call unlink or close in an ensure block, like this:

file ='foo)
begin something with file...
   file.unlink   # deletes the temp file

Unlink after creation

On POSIX systems, it’s possible to unlink a file right after creating it, and before closing it. This removes the filesystem entry without closing the file handle, so it ensures that only the processes that already had the file handle open can access the file’s contents. It’s strongly recommended that you do this if you do not want any other processes to be able to read from or write to the Tempfile, and you do not need to know the Tempfile’s filename either.

For example, a practical use case for unlink-after-creation would be this: you need a large byte buffer that’s too large to comfortably fit in RAM, e.g. when you’re writing a web server and you want to buffer the client’s file upload data.

Please refer to unlink for more information and a code example.

Minor notes

Tempfile’s filename picking method is both thread-safe and inter-process-safe: it guarantees that no other threads or processes will pick the same filename.

Tempfile itself however may not be entirely thread-safe. If you access the same Tempfile object from multiple threads then you should protect it with a mutex.


public class

  1. new
  2. open

public instance

  1. close
  2. close!
  3. delete
  4. length
  5. open
  6. path
  7. size
  8. unlink
  9. unlinked?

Public class methods

new(basename, [tmpdir = Dir.tmpdir], [options])

Creates a temporary file with permissions 0600 (= only readable and writable by the owner) and opens it with mode “w+”.

The basename parameter is used to determine the name of the temporary file. You can either pass a String or an Array with 2 String elements. In the former form, the temporary file’s base name will begin with the given string. In the latter form, the temporary file’s base name will begin with the array’s first element, and end with the second element. For example:

file ='hello')
file.path  # => something like: "/tmp/foo2843-8392-92849382--0"

# Use the Array form to enforce an extension in the filename:
file =['hello', '.jpg'])
file.path  # => something like: "/tmp/foo2843-8392-92849382--0.jpg"

The temporary file will be placed in the directory as specified by the tmpdir parameter. By default, this is Dir.tmpdir (see ‘tmpdir.rb’ in the Ruby standard library.) When $SAFE > 0 and the given tmpdir is tainted, it uses ’/tmp’ as the temporary directory. Please note that ENV values are tainted by default, and Dir.tmpdir’s return value might come from environment variables (e.g. $TMPDIR).

file ='hello', '/home/aisaka')
file.path  # => something like: "/home/aisaka/foo2843-8392-92849382--0"

You can also pass an options hash. Under the hood, Better::Tempfile creates the temporary file using These options will be passed to This is mostly useful on Ruby 1.9 for specifying encoding options, e.g.:'hello', '/home/aisaka', :encoding => 'ascii-8bit')

# You can also omit the 'tmpdir' parameter:'hello', :encoding => 'ascii-8bit')


Under rare circumstances, this constructor can raise an instance of Better::Tempfile::CreationError. This could happen if a large number of threads or processes are simultaneously trying to create temp files and stepping on each others’ toes. If cannot find a unique filename within a limited number of tries, then it will raise this exception.

[show source]
# File lib/better/tempfile.rb, line 214
  def initialize(basename, *rest)
    # I wish keyword argument settled soon.
    if rest.last.respond_to?(:to_hash)
      opts = rest.last.to_hash
      opts = nil
    tmpdir = rest[0] || Dir::tmpdir
    if $SAFE > 0 && tmpdir.tainted?
      tmpdir = '/tmp'

    lock = tmpname = nil
    n = failure = 0
    @@lock.synchronize do
          tmpname = File.join(tmpdir, make_tmpname(basename, n))
          lock = tmpname + '.lock'
          n += 1
        end while @@live_tempfiles.include?(tmpname) ||
                  File.exist?(lock) ||
      rescue SystemCallError
        failure += 1
        retry if failure < MAX_TRIES
        raise CreationError, ("cannot generate tempfile `%s'" % tmpname)

    @finalizer_info = [tmpname]
    @finalizer_callback = self.class.create_finalizer_callback(@finalizer_info)
    ObjectSpace.define_finalizer(self, @finalizer_callback)

    if opts.nil?
      opts = []
      opts = [opts]
    @tmpfile =, File::RDWR | File::CREAT | File::EXCL, 0600, *opts)
    @tmpname = tmpname
    @@live_tempfiles << tmpname
    @finalizer_info[1] = @tmpfile
    @finalizer_info[2] = @@live_tempfiles


    # Now we have all the File/IO methods defined, you must not
    # carelessly put bare puts(), etc. after this.

open (*args) {|tempfile| ...}

Creates a new Tempfile.

If no block is given, this is a synonym for

If a block is given, then a Tempfile object will be constructed, and the block is run with said object as argument. The Tempfile oject will be automatically closed after the block terminates. The call returns the value of the block.

In any case, all arguments (+*args+) will be passed to'foo', '/home/temp') do |f|
   ... do something with f ...

# Equivalent:
f ='foo', '/home/temp')
   ... do something with f ...
[show source]
# File lib/better/tempfile.rb, line 132
    def open(*args)
      tempfile = new(*args)

      if block_given?

Public instance methods

close (unlink_now = false)

Closes the file. If unlink_now is true, then the file will be unlinked (deleted) after closing. Of course, you can choose to later call unlink if you do not unlink it now.

[show source]
# File lib/better/tempfile.rb, line 280
  def close(unlink_now = false)
    if unlink_now
close! ()

Closes and unlinks (deletes) the file. Has the same effect as called close(true).

[show source]
# File lib/better/tempfile.rb, line 290
  def close!
    unlink if !unlinked?
delete ()

Alias for unlink

length ()

Alias for size

open ()

Opens or reopens the file with mode “r+”.

[show source]
# File lib/better/tempfile.rb, line 270
  def open
    @tmpfile.close if @tmpfile
    @tmpfile =, 'r+')
    @finalizer_info[1] = @tmpfile
path ()

Returns the full path name of the temporary file. This will be nil if unlink has been called.

[show source]
# File lib/better/tempfile.rb, line 350
  def path
size ()

Returns the size of the temporary file. As a side effect, the IO buffer is flushed before determining the size.

[show source]
# File lib/better/tempfile.rb, line 356
  def size
    if @tmpfile
unlink ()

Unlinks (deletes) the file from the filesystem. One should always unlink the file after using it, as is explained in the “Explicit close” good practice section in the Tempfile overview:

file ='foo)
begin something with file...
   file.unlink   # deletes the temp file


On POSIX systems it’s possible to unlink a file before closing it. This practice is explained in detail in the Tempfile overview (section “Unlink after creation”); please refer there for more information.

However, unlink-before-close may not be supported on non-POSIX operating systems. Microsoft Windows is the most notable case: unlinking a non-closed file will result in an error, which this method will silently ignore. If you want to practice unlink-before-close whenever possible, then you should write code like this:

file ='foo')
file.unlink   # On Windows this silently fails.
   ... do something with file ...
   file.close!   # Closes the file handle. If the file wasn't unlinked
                 # because #unlink failed, then this method will attempt
                 # to do so again.
[show source]
# File lib/better/tempfile.rb, line 328
  def unlink
      if File.exist?(@tmpname) # keep this order for thread safeness
      @finalizer_info = @tmpname = nil
    rescue Errno::EACCES
      # may not be able to unlink on Windows; just ignore
unlinked? ()

Returns whether unlink has been called on this Tempfile, and whether it succeeded.

[show source]
# File lib/better/tempfile.rb, line 344
  def unlinked?