Is there something like a null-stream in Ruby?

Question

I could use:

File.open('/dev/null', 'w')

on Unix systems, but if there is a Ruby way to achieve this, I'd like to use it. I am just looking for an I/O stream, that immediately "trashes" all writes, kind of like a null-object.

If there isn't one already, it'd be insanely easy to make one. Just have a class with write methods that do nothing. — cHao, Dec 30 '11 at 17:02

Marc-André Lafortune · Answer 1 · 2013-03-08T19:16:00.760

83

If you want the full behavior of streams, the best is probably to use:

File.open(File::NULL, "w")

Note that File::NULL is new to Ruby 1.9.3; you can use my backports gem:

require 'backports/1.9.3/file/null' # => Won't do anything in 1.9.3+
File.open(File::NULL, "w")          # => works even in Ruby 1.8.6

You could also copy the relevant code if you prefer.

edited Mar 08 '13 at 19:16

answered Dec 30 '11 at 17:10

Marc-André Lafortune

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That's excellent. This is how I use it: `STDNULL = File.open(File::NULL, 'w')` then I use STDNULL every where – Jagtesh Chadha Jun 26 '15 at 19:31

score 10 · Answer 2 · edited Sep 22 '21 at 18:52

10

There's stringIO, which I find useful when I want to introduce a dummy filestream:

require "stringio"
f = StringIO.new
f.gets # => nil

And here's some code from heckle that finds the bit bucket for both Unix and Windows, slightly modified:

# Is this platform MS Windows-like?
# Actually, I suspect the following line is not very reliable.
WINDOWS = RUBY_PLATFORM =~ /mswin/
# Path to the bit bucket.
NULL_PATH = WINDOWS ? 'NUL:' : '/dev/null'

edited Sep 22 '21 at 18:52

Peter Mortensen

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answered Apr 10 '12 at 04:42

Andrew Grimm

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The StringIO.new trick gets my +1 because it doesn't seem to open a file descriptor, so perhaps doesn't require explicit closing: http://stackoverflow.com/questions/4795447/rubys-file-open-and-the-need-for-f-close – Martin Dorey May 08 '12 at 23:45
2

It doesn't trash input though, so has the potential to cause a memory leak depending on your use case. – Xavier Shay Nov 22 '16 at 23:57

Peter O. · Accepted Answer · 2011-12-30T17:15:37.223

5

No, I don't believe there is anything like a null stream in Ruby, at least in earlier versions. In that case, you must make one yourself. Depending on the methods that it will call, you will need to write stub methods on the null stream class, like this:

class NullStream
   def <<(o); self; end
end

The above example is by no means complete. For example, some streams may require calling the write, puts or other methods. Moreover, some methods should be implemented by returning self in their methods, like <<, others not.

edited Dec 30 '11 at 17:15

answered Dec 30 '11 at 17:03

Peter O.

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That needs to be `def <<(o); self end` to work properly (otherwise `null_stream << foo << bar` will break). – sepp2k Dec 30 '11 at 17:08
This nullifies output only on application or user level (virtual or fake streams, string IOs, etc.), not on system level (real streams, fd, device files, etc.). [Marc-André Lafortune's answer](http://stackoverflow.com/a/8682009/445221) is probably more appropriate. – konsolebox Sep 06 '14 at 06:42

score 2 · Answer 4 · answered Sep 05 '19 at 15:49

2

Logger.new("/dev/null") does the trick

answered Sep 05 '19 at 15:49

Dende

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score 1 · Answer 5 · answered May 21 '14 at 23:41

1

There's a gem called devnull

Ruby implementation of null file (like /dev/null on Un*x, NUL on Windows)

It doesn't interact with the null file, but instead has dummy methods for all the methods that IO objects implement.

answered May 21 '14 at 23:41

Andrew Grimm

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Is there something like a null-stream in Ruby?

5 Answers5