class Tempfile - RDoc Documentation

# class Tempfile

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.

## Synopsis¶ ↑

    require 'tempfile'

    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

## 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 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.open('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.

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 Methods

create(basename="", tmpdir=nil, mode: 0, **options) { |tmpfile| ... } click to toggle source

Creates a temporary file as a usual `File` object (not a `Tempfile`). It does not use finalizer and delegation, which makes it more efficient and reliable.

If no block is given, this is similar to `Tempfile.new` except creating `File` instead of `Tempfile`. In that case, the created file is not removed automatically. You should use `File.unlink` to remove it.

If a block is given, then a `File` object will be constructed, and the block is invoked with the object as the argument. The `File` object will be automatically closed and the temporary file is removed after the block terminates, releasing all resources that the block created. The call returns the value of the block.

In any case, all arguments (`basename`, `tmpdir`, `mode`, and `**options`) will be treated the same as for `Tempfile.new`.

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

    # File lib/tempfile.rb, line 349
    def Tempfile.create(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

new(basename="", tmpdir=nil, mode: 0, **options) click to toggle source

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

It is recommended to use `Tempfile.create` { … } instead when possible, because that method avoids the cost of delegation and does not rely on a finalizer to close and unlink the file, which is unreliable.

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 = Tempfile.new('hello')
    file.path  # => something like: "/tmp/hello2843-8392-92849382--0"

    # Use the Array form to enforce an extension in the filename:
    file = Tempfile.new(['hello', '.jpg'])
    file.path  # => something like: "/tmp/hello2843-8392-92849382--0.jpg"

The temporary file will be placed in the directory as specified by the `tmpdir` parameter. By default, this is `Dir.tmpdir`.

    file = Tempfile.new('hello', '/home/aisaka')
    file.path  # => something like: "/home/aisaka/hello2843-8392-92849382--0"

You can also pass an options hash. Under the hood, `Tempfile` creates the temporary file using `File.open`. These options will be passed to `File.open`. This is mostly useful for specifying encoding options, e.g.:

    Tempfile.new('hello', '/home/aisaka', encoding: 'ascii-8bit')

    # You can also omit the 'tmpdir' parameter:
    Tempfile.new('hello', encoding: 'ascii-8bit')

Note: `mode` keyword argument, as accepted by `Tempfile`, can only be numeric, combination of the modes defined in `File::Constants`.

### Exceptions¶ ↑

If `Tempfile.new` cannot find a unique filename within a limited number of tries, then it will raise an exception.

Calls superclass method

    # File lib/tempfile.rb, line 134
    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
      ::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(self, Remover.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 312
    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

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 168
    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 175
    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 150
    def open
      _close
      mode = @mode & ~(File::CREAT|File::EXCL)
      @tmpfile = File.open(@tmpfile.path, mode, **@opts)
      __setobj__(@tmpfile)
    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 228
    def path
      @unlinked ? nil : @tmpfile.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 234
    def size
      if !@tmpfile.closed?
        @tmpfile.size # File#size calls rb_io_flush_raw()
      else
        File.size(@tmpfile.path)
      end
    end

Also aliased as: length
unlink() click to toggle source

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 212
    def unlink
      return if @unlinked
      begin
        File.unlink(@tmpfile.path)
      rescue Errno::ENOENT
      rescue Errno::EACCES
        # may not be able to unlink on Windows; just ignore
        return
      end
      ObjectSpace.undefine_finalizer(self)
      @unlinked = true
    end

Also aliased as: delete