module Kernel

def capture(stream)

stream # => "error\n"
stream = capture(:stderr) { system('echo error 1>&2') }

stream # => "notice\n"
stream = capture(:stdout) { system('echo notice') }

even for subprocesses:

stream # => "error\n"
stream = capture(:stderr) { warn 'error' }

stream # => "notice\n"
stream = capture(:stdout) { puts 'notice' }

Captures the given stream and returns it: 
def capture(stream)
  ActiveSupport::Deprecation.warn(
    "`#capture(stream)` is deprecated and will be removed in the next release."
  ) #not thread-safe
  stream = stream.to_s
  captured_stream = Tempfile.new(stream)
  stream_io = eval("$#{stream}")
  origin_stream = stream_io.dup
  stream_io.reopen(captured_stream)
  yield
  stream_io.rewind
  return captured_stream.read
ensure
  captured_stream.close
  captured_stream.unlink
  stream_io.reopen(origin_stream)
end

def class_eval(*args, &block)

class_eval on an object acts like singleton_class.class_eval. 
def class_eval(*args, &block)
  singleton_class.class_eval(*args, &block)
end

def concern(topic, &module_definition)

See Module::Concerning for more.

A shortcut to define a toplevel concern, not within a module. 
def concern(topic, &module_definition)
  Object.concern topic, &module_definition
end

def debugger

Starts a debugging session if the +debugger+ gem has been loaded (call rails server --debugger to do load it). 
def debugger
  message = "\n***** Debugger requested, but was not available (ensure the debugger gem is listed in Gemfile/installed as gem): Start server with --debugger to enable *****\n"
  defined?(Rails.logger) ? Rails.logger.info(message) : $stderr.puts(message)
end

def enable_warnings

original value afterwards.
Sets $VERBOSE to +true+ for the duration of the block and back to its 
def enable_warnings
  with_warnings(true) { yield }
end

def quietly

This method is not thread-safe.

quietly { system 'bundle install' }

Silences both STDOUT and STDERR, even for subprocesses. 
def quietly
  ActiveSupport::Deprecation.warn(
    "`#quietly` is deprecated and will be removed in the next release."
  ) #not thread-safe
  silence_stream(STDOUT) do
    silence_stream(STDERR) do
      yield
    end
  end
end

def silence_stderr #:nodoc:

:nodoc:
For compatibility 
def silence_stderr #:nodoc:
  ActiveSupport::Deprecation.warn(
    "`#silence_stderr` is deprecated and will be removed in the next release."
  ) #not thread-safe
  silence_stream(STDERR) { yield }
end

def silence_stream(stream)

This method is not thread-safe.

puts 'But this will'

end
puts 'This will never be seen'
silence_stream(STDOUT) do

Silences any stream for the duration of the block.
Deprecated : this method is not thread safe 
def silence_stream(stream)
  old_stream = stream.dup
  stream.reopen(RbConfig::CONFIG['host_os'] =~ /mswin|mingw/ ? 'NUL:' : '/dev/null')
  stream.sync = true
  yield
ensure
  stream.reopen(old_stream)
  old_stream.close
end

def silence_warnings

noisy_call # warning voiced

end
value = noisy_call # no warning voiced
silence_warnings do

value afterwards.
Sets $VERBOSE to nil for the duration of the block and back to its original 
def silence_warnings
  with_warnings(nil) { yield }
end

def suppress(*exception_classes)

puts 'This code gets executed and nothing related to ZeroDivisionError was seen'

end
puts 'This code is NOT reached'
1/0
suppress(ZeroDivisionError) do

Blocks and ignores any exception passed as argument if raised within the block. 
def suppress(*exception_classes)
  yield
rescue *exception_classes
end

def with_warnings(flag)

value afterwards.
Sets $VERBOSE for the duration of the block and back to its original 
def with_warnings(flag)
  old_verbose, $VERBOSE = $VERBOSE, flag
  yield
ensure
  $VERBOSE = old_verbose
end