From: "jonforums (Jon Forums)" Date: 2012-09-28T04:01:05+09:00 Subject: [ruby-core:47715] [ruby-trunk - Bug #7070] sometimes backticks can fail to return data Issue #7070 has been updated by jonforums (Jon Forums). While I can repro with this snippet on Win7 32bit, your ffmpeg command (nonexistent 'dummy' input file?) appears to be causing the problem. # file: backtick_loop.rb CYCLES = (ENV['BT_TEST_CYCLES'] ||= '200').to_i puts 'backticking curl...' CYCLES.times do |i| data = `curl --manual` abort "[#{i}] backticked curl returned no data" if data.nil? or data.empty? end puts 'backticking ffmpeg...' CYCLES.times do |i| data = `C:/Users/Jon/Documents/FFmpeg/bin/ffmpeg.exe -list_devices true -f dshow -i dummy 2>&1` abort "[#{i}] backticked ffmpeg returned no data" if data.nil? or data.empty? end puts 'OK' ### results ### C:\Users\Jon\Documents\RubyDev\sandbox>pik ruby backtick_loop.rb ruby 1.8.7 (2012-06-29 patchlevel 370) [i386-mingw32] backticking curl... backticking ffmpeg... [15] backticked ffmpeg returned no data ruby 1.9.3p125 (2012-02-16) [i386-mingw32] backticking curl... backticking ffmpeg... [7] backticked ffmpeg returned no data ruby 1.9.3p277 (2012-09-25 revision 37029) [i386-mingw32] backticking curl... backticking ffmpeg... [4] backticked ffmpeg returned no data tcs-ruby 1.9.3p231 (2012-05-25, TCS patched 2012-05-27) [i386-mingw32] backticking curl... backticking ffmpeg... [2] backticked ffmpeg returned no data ruby 2.0.0dev (2012-09-26 trunk 37036) [i386-mingw32] backticking curl... backticking ffmpeg... [30] backticked ffmpeg returned no data But given the following cmd.exe ffmpeg invocation ends with the error "dummy: Immediate exit requested" I suspect your ffmpeg command is the cause of the problem. When I remove the `-i dummy` part (nonexistent input file) I haven't been able to repro using the above script. Try it on your system and see if the failure persists. C:\Users\Jon\Documents\RubyDev\sandbox>C:\Users\Jon\Documents\FFmpeg\bin\ffmpeg.exe -list_devices true -f dshow -i dummy 2>&1 ffmpeg version N-44727-gbbe9fe4 Copyright (c) 2000-2012 the FFmpeg developers built on Sep 24 2012 16:51:07 with gcc 4.7.1 (GCC) configuration: --enable-gpl --enable-version3 --disable-pthreads --enable-runtime-cpudetect --enable-avisynth --enable-bzlib --enable-frei0r --enable-libass --enable-libcelt --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libfreetype --enable-libgsm --enable-libmp3lame --enable-libnut --enable-libopenjpeg --enable-librtmp --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libutvideo --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxavs --enable-libxvid --enable-zlib libavutil 51. 73.101 / 51. 73.101 libavcodec 54. 58.100 / 54. 58.100 libavformat 54. 28.101 / 54. 28.101 libavdevice 54. 2.101 / 54. 2.101 libavfilter 3. 17.100 / 3. 17.100 libswscale 2. 1.101 / 2. 1.101 libswresample 0. 15.100 / 0. 15.100 libpostproc 52. 0.100 / 52. 0.100 [dshow @ 0036c260] DirectShow video devices [dshow @ 0036c260] "Integrated Webcam" [dshow @ 0036c260] "Google Camera Adapter 0" [dshow @ 0036c260] "Google Camera Adapter 1" [dshow @ 0036c260] DirectShow audio devices [dshow @ 0036c260] "Microphone (High Definition Aud" dummy: Immediate exit requested C:\Users\Jon\Documents\RubyDev\sandbox>echo %errorlevel% 1 ---------------------------------------- Bug #7070: sometimes backticks can fail to return data https://bugs.ruby-lang.org/issues/7070#change-29765 Author: rogerdpack (Roger Pack) Status: Open Priority: Normal Assignee: Category: Target version: ruby -v: ruby 1.9.3p194 (2012-04-20) [i386-mingw32] Basically, if you have ffmpeg for windows, ex: http://ffmpeg.zeranoe.com/builds Then run it like this: enum = `ffmpeg.exe -list_devices true -f dshow -i dummy 2>&1` "every so often" the value returned is "" (presumably in error). Example: 39 times you'll get this: >> enum = `temp\\ffmpeg.exe -list_devices true -f dshow -i dummy 2>&1` => "ffmpeg version N-44123-g5d55830 Copyright (c) 2000-2012 the FFmpeg developers\n built on Sep 2 2012 20:23:29 with gcc 4.7.1 (GCC)\n configuration: --enable-gpl --enable-version3 --disable-pthreads --enable-runtime-cpudetect --enable-avisynth --enable-bzlib --enable-frei0r --enable-libass --enable-libcelt --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libfreetype --enable-libgsm --enable-libmp3lame --enable-libnut --enable-libopenjpeg --enable-librtmp --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libutvideo --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxavs --enable-libxvid --enable-zlib\n libavutil 51. 70.100 / 51. 70.100\n libavcodec 54. 55.100 / 54. 55.100\n libavformat 54. 25.104 / 54. 25.104\n libavdevice 54. 2.100 / 54. 2.100\n libavfilter 3. 15.102 / 3. 15.102\n libswscale 2. 1.101 / 2. 1.101\n libswresample 0. 15.100 / 0. 15.100\n libpostproc 52. 0.100 / 52. 0.100\n[dshow @ 003cc3a0] DirectShow video devices\n[dshow @ 003cc3a0] \"screen-capture-recorder\"\n[dshow @ 003cc3a0] DirectShow audio devices\n[dshow @ 003cc3a0] \"Microphone (USB Audio Device)\"\n[dshow @ 003cc3a0] \"virtual-audio-capturer\"\ndummy: Immediate exit requested\n" irb(main):036:0> enum = `temp\\ffmpeg.exe -list_devices true -f dshow -i dummy 2>&1` then the 40th will be >> enum = `temp\\ffmpeg.exe -list_devices true -f dshow -i dummy 2>&1` => "" Running using C's "popen" seems to work reliably. https://gist.github.com/3784971 I would note that jruby seems to suffer from the same difficulty for whatever reason. Running it with other executables Thanks! -- http://bugs.ruby-lang.org/