class Tempfile
A utility class for managing temporary files.
There are two kind of methods of creating a temporary file:
-
Tempfile.create
(recommended) -
Tempfile.new
andTempfile.open
(mostly for backward compatibility, not recommended)
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:
-
Long
GC
intervals and conservativeGC
can accumulate temporary files that are not removed. -
Temporary files are not removed if Ruby exits abnormally (such as SIGKILL, SEGV).
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
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:
-
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 withprefix
and ends withsuffix
: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 inFile::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 558 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
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 superclassDelegateClass(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 inTempfile.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 withprefix
and ends withsuffix
: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 inFile::Constants
. -
For
options
, see Open Options.
Related: Tempfile.create
.
# 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 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 super(tmpfile) @finalizer_manager = FinalizerManager.new(__getobj__.path) @finalizer_manager.register(self, __getobj__) end
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 439 def open(*args, **kw) tempfile = new(*args, **kw) if block_given? begin yield(tempfile) ensure tempfile.close end else tempfile end end
Public Instance Methods
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 279 def close(unlink_now=false) _close unlink if unlink_now end
Closes and unlinks (deletes) the file. Has the same effect as called close(true)
.
# File lib/tempfile.rb, line 286 def close! close(true) end
Opens or reopens the file with mode “r+”.
# File lib/tempfile.rb, line 257 def open _close mode = @mode & ~(File::CREAT|File::EXCL) __setobj__(File.open(__getobj__.path, mode, **@opts)) @finalizer_manager.register(self, __getobj__) __getobj__ end
Returns the full path name of the temporary file. This will be nil if unlink
has been called.
# File lib/tempfile.rb, line 341 def path @unlinked ? nil : __getobj__.path end
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 347 def size if !__getobj__.closed? __getobj__.size # File#size calls rb_io_flush_raw() else File.size(__getobj__.path) end end
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 = Tempfile.new('foo') begin # ...do something with file... ensure file.close file.unlink # deletes the temp file end
Unlink-before-close¶ ↑
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 = Tempfile.new('foo') file.unlink # On Windows this silently fails. begin # ... do something with file ... ensure file.close! # Closes the file handle. If the file wasn't unlinked # because #unlink failed, then this method will attempt # to do so again. end
# File lib/tempfile.rb, line 323 def unlink return if @unlinked begin File.unlink(__getobj__.path) rescue Errno::ENOENT rescue Errno::EACCES # may not be able to unlink on Windows; just ignore return end @finalizer_manager.unlinked = true @unlinked = true end