Temporarily suppress STDOUT and STDERR (ruby)

suppress_ruby_output.rb

# Temporarily redirects STDOUT and STDERR to /dev/null
# but does print exceptions should there occur any.
# Call as:
#   suppress_output { puts 'never printed' }
#
def suppress_output
  original_stderr = $stderr.clone
  original_stdout = $stdout.clone
  $stderr.reopen(File.new('/dev/null', 'w'))
  $stdout.reopen(File.new('/dev/null', 'w'))
  yield
ensure
  $stdout.reopen(original_stdout)
  $stderr.reopen(original_stderr)
end

very nice. i used this for running my sinatra app during some high level cucumber tests. these test used to mix in the sinatra logs with my test output, got very annoying/messy

Fantastic! Thank you, this is exactly what I was looking for. (I also used it to stop output from an inline Sinatra app :)

I believe it can be simplified quite a bit:

• the begin / end is unnecessary since the rescue and ensure clauses can be hooked onto the method itself (I love Ruby!)
• the rescue clause is unnecessary since the ensure clause will run anyway before the exception is passed on up the call stack, meaning output will be turned back on before the exception has a chance to get caught (or not) by the calling code
• the retval is unnecessary since the return value of the method will be the result of yielding to the block anyway
• which means that retval = is also unnecessary

Putting that all together, it now looks like this:

def suppress_output
  original_stdout, original_stderr = $stdout.clone, $stderr.clone
  $stderr.reopen File.new('/dev/null', 'w')
  $stdout.reopen File.new('/dev/null', 'w')
  yield
ensure
  $stdout.reopen original_stdout
  $stderr.reopen original_stderr
end

👍 @iamtheiconoclast

👍 🎉

Nice one guys! Very useful :)

Awesome little ditty.

How can this be edited to instead of just suppressing by sending to dev/null, it instead returned the output so that it can be stored in a variable? Can this be done without redirecting to a file?

@nancy-gomez, for this you might want to use https://docs.ruby-lang.org/en/2.5.0/Open3.html#method-c-popen3

@iamtheiconoclast I realise I never looked at the comments here. 😅 Thanks for your suggested simplifications; I've amended the Gist to reflect them.

Windows Version with File::NULL

# Temporarily redirects STDOUT and STDERR to /dev/null
# but does print exceptions should there occur any.
# Call as:
#   suppress_output { puts 'never printed' }
#
def suppress_output
  original_stderr = $stderr.clone
  original_stdout = $stdout.clone
  $stderr.reopen(File.new(File::NULL, 'w'))
  $stdout.reopen(File.new(File::NULL, 'w'))
  yield
ensure
  $stdout.reopen(original_stdout)
  $stderr.reopen(original_stderr)
end

FYI https://stackoverflow.com/questions/1496019/suppresing-output-to-console-with-ruby/1496040#1496040