How do I temporarily redirect stderr in Ruby?

Question

I\'d like to temporarily redirect stderr in a Ruby script for the duration of a block, ensuring that I reset it to its original value at the end of the block.

I had

Answer 1

I like the StringIO answers. But if you are calling an external process, and $stderr = StringIO.new doesn't work, you might write stderr out to a temporary file:

require 'tempfile'

def capture_stderr
  backup_stderr = STDERR.dup
  begin
    Tempfile.open("captured_stderr") do |f|
      STDERR.reopen(f)
      yield
      f.rewind
      f.read
    end
  ensure
    STDERR.reopen backup_stderr
  end
end