class Tempfile

A utility class for managing temporary files.

There are two kind of methods of creating a temporary file:

Tempfile.create creates a usual File object. The timing of file deletion is predictable. Also, it supports open-and-unlink technique which removes the temporary file immediately after creation.

Tempfile.new and Tempfile.open creates a Tempfile object. The created file is removed by the GC (finalizer). The timing of file deletion is not predictable.

Synopsis

require 'tempfile'

# Tempfile.create with a block
# The filename are choosen automatically.
# (You can specify the prefix and suffix of the filename by an optional argument.)
Tempfile.create {|f|
  f.puts "foo"
  f.rewind
  f.read                # => "foo\n"
}                       # The file is removed at block exit.

# Tempfile.create without a block
# You need to unlink the file in non-block form.
f = Tempfile.create
f.puts "foo"
f.close
File.unlink(f.path)     # You need to unlink the file.

# Tempfile.create(anonymous: true) without a block
f = Tempfile.create(anonymous: true)
# The file is already removed because anonymous.
f.path                  # => "/tmp/"  (no filename since no file)
f.puts "foo"
f.rewind
f.read                  # => "foo\n"
f.close

# Tempfile.create(anonymous: true) with a block
Tempfile.create(anonymous: true) {|f|
  # The file is already removed because anonymous.
  f.path                # => "/tmp/"  (no filename since no file)
  f.puts "foo"
  f.rewind
  f.read                # => "foo\n"
}

# Not recommended: Tempfile.new without a block
file = Tempfile.new('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
file.read      # => "hello world"
file.close
file.unlink    # deletes the temp file

About Tempfile.new and Tempfile.open

This section does not apply to Tempfile.create because it returns a File object (not a Tempfile object).

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.

A Tempfile object has a finalizer to remove the temporary file. This means that the temporary file is removed via GC. This can cause several problems:

There are legacy good practices for Tempfile.new and Tempfile.open as follows.

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 it’s unnecessary to explicitly delete a Tempfile after use, though it’s a good practice to do so: not explicitly deleting unused Tempfiles can potentially leave behind a large number of temp files on the filesystem until they’re garbage collected. The existence 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 = Tempfile.new('foo')
begin
   # ...do something with file...
ensure
   file.close
   file.unlink   # deletes the temp file
end

Tempfile.create { … } exists for this purpose and is more convenient to use. Note that Tempfile.create returns a File instance instead of a Tempfile, which also avoids the overhead and complications of delegation.

Tempfile.create('foo') do |file|
   # ...do something with file...
end

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.

Also, this guarantees the temporary file is removed even if Ruby exits abnormally. The OS reclaims the storage for the temporary file when the file is closed or the Ruby process exits (normally or abnormally).

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.

‘Tempfile.create(anonymous: true)` supports this behavior. It also works on Windows.

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.

Constants

VERSION

The version

Public Class Methods

create(basename="", tmpdir=nil, mode: 0, anonymous: false, **options, &block) click to toggle source

Creates a file in the underlying file system; returns a new File object based on that file.

With no block given and no arguments, creates and returns file whose:

  • Class is File (not Tempfile).

  • Directory is the system temporary directory (system-dependent).

  • Generated filename is unique in that directory.

  • Permissions are 0600; see File Permissions.

  • Mode is 'w+' (read/write mode, positioned at the end).

The temporary file removal depends on the keyword argument anonymous and whether a block is given or not. See the description about the anonymous keyword argument later.

Example:

f = Tempfile.create     # => #<File:/tmp/20220505-9795-17ky6f6>
f.class                 # => File
f.path                  # => "/tmp/20220505-9795-17ky6f6"
f.stat.mode.to_s(8)     # => "100600"
f.close
File.exist?(f.path)     # => true
File.unlink(f.path)
File.exist?(f.path)     # => false

Tempfile.create {|f|
  f.puts "foo"
  f.rewind
  f.read                # => "foo\n"
  f.path                # => "/tmp/20240524-380207-oma0ny"
  File.exist?(f.path)   # => true
}                       # The file is removed at block exit.

f = Tempfile.create(anonymous: true)
# The file is already removed because anonymous
f.path                  # => "/tmp/"  (no filename since no file)
f.puts "foo"
f.rewind
f.read                  # => "foo\n"
f.close

Tempfile.create(anonymous: true) {|f|
  # The file is already removed because anonymous
  f.path                # => "/tmp/"  (no filename since no file)
  f.puts "foo"
  f.rewind
  f.read                # => "foo\n"
}

The argument basename, if given, may be one of the following:

  • A string: the generated filename begins with basename:

    Tempfile.create('foo') # => #<File:/tmp/foo20220505-9795-1gok8l9>
    
  • An array of two strings [prefix, suffix]: the generated filename begins with prefix and ends with suffix:

    Tempfile.create(%w/foo .jpg/) # => #<File:/tmp/foo20220505-17839-tnjchh.jpg>
    

With arguments basename and tmpdir, the file is created in the directory tmpdir:

Tempfile.create('foo', '.') # => #<File:./foo20220505-9795-1emu6g8>

Keyword arguments mode and options are passed directly to the method File.open:

  • The value given for mode must be an integer and may be expressed as the logical OR of constants defined in File::Constants.

  • For options, see Open Options.

The keyword argument anonymous specifies when the file is removed.

  • +anonymous=false+ (default) without a block: the file is not removed.

  • +anonymous=false+ (default) with a block: the file is removed after the block exits.

  • +anonymous=true+ without a block: the file is removed before returning.

  • +anonymous=true+ with a block: the file is removed before the block is called.

In the first case (+anonymous=false+ without a block), the file is not removed automatically. It should be explicitly closed. It can be used to rename to the desired filename. If the file is not needed, it should be explicitly removed.

The +File#path+ method of the created file object returns the temporary directory with a trailing slash when anonymous is true.

When a block is given, it creates the file as described above, passes it to the block, and returns the block’s value. Before the returning, the file object is closed and the underlying file is removed:

Tempfile.create {|file| file.path } # => "/tmp/20220505-9795-rkists"

Implementation note:

The keyword argument +anonymous=true+ is implemented using FILE_SHARE_DELETE on Windows. O_TMPFILE is used on Linux.

Related: Tempfile.new.

# File lib/tempfile.rb, line 554
def Tempfile.create(basename="", tmpdir=nil, mode: 0, anonymous: false, **options, &block)
  if anonymous
    create_anonymous(basename, tmpdir, mode: mode, **options, &block)
  else
    create_with_filename(basename, tmpdir, mode: mode, **options, &block)
  end
end
new(basename="", tmpdir=nil, mode: 0, **options) click to toggle source

Creates a file in the underlying file system; returns a new Tempfile object based on that file.

If possible, consider instead using Tempfile.create, which:

  • Avoids the performance cost of delegation, incurred when Tempfile.new calls its superclass DelegateClass(File).

  • Does not rely on a finalizer to close and unlink the file, which can be unreliable.

Creates and returns file whose:

  • Class is Tempfile (not File, as in Tempfile.create).

  • Directory is the system temporary directory (system-dependent).

  • Generated filename is unique in that directory.

  • Permissions are 0600; see File Permissions.

  • Mode is 'w+' (read/write mode, positioned at the end).

The underlying file is removed when the Tempfile object dies and is reclaimed by the garbage collector.

Example:

f = Tempfile.new # => #<Tempfile:/tmp/20220505-17839-1s0kt30>
f.class               # => Tempfile
f.path                # => "/tmp/20220505-17839-1s0kt30"
f.stat.mode.to_s(8)   # => "100600"
File.exist?(f.path)   # => true
File.unlink(f.path)   #
File.exist?(f.path)   # => false

Argument basename, if given, may be one of:

  • A string: the generated filename begins with basename:

    Tempfile.new('foo') # => #<Tempfile:/tmp/foo20220505-17839-1whk2f>
    
  • An array of two strings [prefix, suffix]: the generated filename begins with prefix and ends with suffix:

    Tempfile.new(%w/foo .jpg/) # => #<Tempfile:/tmp/foo20220505-17839-58xtfi.jpg>
    

With arguments basename and tmpdir, the file is created in directory tmpdir:

Tempfile.new('foo', '.') # => #<Tempfile:./foo20220505-17839-xfstr8>

Keyword arguments mode and options are passed directly to method File.open:

  • The value given with mode must be an integer, and may be expressed as the logical OR of constants defined in File::Constants.

  • For options, see Open Options.

Related: Tempfile.create.

Calls superclass method
# File lib/tempfile.rb, line 219
def initialize(basename="", tmpdir=nil, mode: 0, **options)
  warn "Tempfile.new doesn't call the given block.", uplevel: 1 if block_given?

  @unlinked = false
  @mode = mode|File::RDWR|File::CREAT|File::EXCL
  @finalizer_obj = Object.new
  tmpfile = nil
  ::Dir::Tmpname.create(basename, tmpdir, **options) do |tmpname, n, opts|
    opts[:perm] = 0600
    tmpfile = File.open(tmpname, @mode, **opts)
    @opts = opts.freeze
  end
  ObjectSpace.define_finalizer(@finalizer_obj, Remover.new(tmpfile.path))
  ObjectSpace.define_finalizer(self, Closer.new(tmpfile))

  super(tmpfile)
end
open(*args, **kw) { |tempfile| ... } click to toggle source

Creates a new Tempfile.

This method is not recommended and exists mostly for backward compatibility. Please use Tempfile.create instead, which avoids the cost of delegation, does not rely on a finalizer, and also unlinks the file when given a block.

Tempfile.open is still appropriate if you need the Tempfile to be unlinked by a finalizer and you cannot explicitly know where in the program the Tempfile can be unlinked safely.

If no block is given, this is a synonym for Tempfile.new.

If a block is given, then a Tempfile object will be constructed, and the block is run with the Tempfile object as argument. The Tempfile object will be automatically closed after the block terminates. However, the file will not be unlinked and needs to be manually unlinked with Tempfile#close! or Tempfile#unlink. The finalizer will try to unlink but should not be relied upon as it can keep the file on the disk much longer than intended. For instance, on CRuby, finalizers can be delayed due to conservative stack scanning and references left in unused memory.

The call returns the value of the block.

In any case, all arguments (*args) will be passed to Tempfile.new.

Tempfile.open('foo', '/home/temp') do |f|
   # ... do something with f ...
end

# Equivalent:
f = Tempfile.open('foo', '/home/temp')
begin
   # ... do something with f ...
ensure
   f.close
end
# File lib/tempfile.rb, line 435
def open(*args, **kw)
  tempfile = new(*args, **kw)

  if block_given?
    begin
      yield(tempfile)
    ensure
      tempfile.close
    end
  else
    tempfile
  end
end

Private Class Methods

create_anonymous(basename="", tmpdir=nil, mode: 0, **options) { |tmpfile| ... } click to toggle source
# File lib/tempfile.rb, line 592
        def create_anonymous(basename="", tmpdir=nil, mode: 0, **options, &block)
  tmpfile = nil
  tmpdir = Dir.tmpdir() if tmpdir.nil?
  if defined?(File::TMPFILE) # O_TMPFILE since Linux 3.11
    begin
      tmpfile = File.open(tmpdir, File::RDWR | File::TMPFILE, 0600)
    rescue Errno::EISDIR, Errno::ENOENT, Errno::EOPNOTSUPP
      # kernel or the filesystem does not support O_TMPFILE
      # fallback to create-and-unlink
    end
  end
  if tmpfile.nil?
    mode |= File::SHARE_DELETE | File::BINARY # Windows needs them to unlink the opened file.
    tmpfile = create_with_filename(basename, tmpdir, mode: mode, **options)
    File.unlink(tmpfile.path)
  end
  path = File.join(tmpdir, '')
  if tmpfile.path != path
    # clear path.
    tmpfile.autoclose = false
    tmpfile = File.new(tmpfile.fileno, mode: File::RDWR, path: path)
  end
  if block
    begin
      yield tmpfile
    ensure
      tmpfile.close
    end
  else
    tmpfile
  end
end
create_with_filename(basename="", tmpdir=nil, mode: 0, **options) { |tmpfile| ... } click to toggle source
# File lib/tempfile.rb, line 563
        def create_with_filename(basename="", tmpdir=nil, mode: 0, **options)
  tmpfile = nil
  Dir::Tmpname.create(basename, tmpdir, **options) do |tmpname, n, opts|
    mode |= File::RDWR|File::CREAT|File::EXCL
    opts[:perm] = 0600
    tmpfile = File.open(tmpname, mode, **opts)
  end
  if block_given?
    begin
      yield tmpfile
    ensure
      unless tmpfile.closed?
        if File.identical?(tmpfile, tmpfile.path)
          unlinked = File.unlink tmpfile.path rescue nil
        end
        tmpfile.close
      end
      unless unlinked
        begin
          File.unlink tmpfile.path
        rescue Errno::ENOENT
        end
      end
    end
  else
    tmpfile
  end
end

Public Instance Methods

close(unlink_now=false) click to toggle source

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.

If you don’t explicitly unlink the temporary file, the removal will be delayed until the object is finalized.

# File lib/tempfile.rb, line 277
def close(unlink_now=false)
  _close
  unlink if unlink_now
end
close!() click to toggle source

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

# File lib/tempfile.rb, line 284
def close!
  close(true)
end
delete()
Alias for: unlink
length()
Alias for: size
open() click to toggle source

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

# File lib/tempfile.rb, line 257
def open
  _close
  ObjectSpace.undefine_finalizer(self)
  mode = @mode & ~(File::CREAT|File::EXCL)
  __setobj__(File.open(__getobj__.path, mode, **@opts))
  ObjectSpace.define_finalizer(self, Closer.new(__getobj__))
  __getobj__
end
path() click to toggle source

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

# File lib/tempfile.rb, line 337
def path
  @unlinked ? nil : __getobj__.path
end
size() click to toggle source

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

# File lib/tempfile.rb, line 343
def size
  if !__getobj__.closed?
    __getobj__.size # File#size calls rb_io_flush_raw()
  else
    File.size(__getobj__.path)
  end
end
Also aliased as: length