Question

• I am running a Ruby gem which relies on a C extension (not a call to system).
• The C code makes several calls to printf.
• I want to silence the output of these calls.
• Changing Ruby’s STDOUT (example) or STDERR does not prevent the text from being output.

Is it possible to do this without modifying the C code? If so, how?

Answer 1

Someone originally commented on my post suggesting to use IO.reopen. This worked for me. The person has unfortunately since deleted his/her comment, so I’m posting the more detailed function I used in the end:

def silence_stdout(log = '/dev/null')
  old = $stdout.dup
  $stdout.reopen(File.new(log, 'w'))
  yield
  $stdout = old
end

Usage:

silence_stdout { foo }              # Won't be displayed, won't be logged.
silence_stdout('log.txt') { bar }   # Won't be displayed, logged in log.txt.