# I'm a process-spawning idiot **URL:** \ **Category:** Ruby\ **Created:** [November 29, 2006, 8:02am UTC](https://www.ruby-forum.com/t/im-a-process-spawning-idiot/77625 "2006-11-29T08:02:19Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![twifkak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/a88e4f/32.png) [@twifkak](https://www.ruby-forum.com/u/twifkak)\ **Post date:** [November 29, 2006, 8:02am UTC](https://www.ruby-forum.com/t/im-a-process-spawning-idiot/77625/1 "2006-11-29T08:02:19Z")
I’m looking for a method that, like Kernel#`and IO::popen, allows me to call out to the system and grab its stdout. However, I'd like it to accept multiple args (like Kernel#system), so I don't have to worry about filenames with spaces and backslashes and the like. Alternatively, I'll take a lib that escapes strings for Kernel#`, provided it works on win32, unix, cygwin… I’m sure I’m just missing the obvious. Help? Thanks, Devin ---
**Author:** ![twifkak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/a88e4f/32.png) [@twifkak](https://www.ruby-forum.com/u/twifkak)\ **Post date:** [November 29, 2006, 8:50am UTC](https://www.ruby-forum.com/t/im-a-process-spawning-idiot/77625/2 "2006-11-29T08:50:26Z")
Devin M. wrote: > I’m looking for a method that, like Kernel#`and IO::popen, allows me to call out to the system and grab its stdout. However, I'd like it to accept multiple args (like Kernel#system), so I don't have to worry about filenames with spaces and backslashes and the like. Alternatively, I'll take a lib that escapes strings for Kernel#`, provided it works on > win32, unix, cygwin… > > I’m sure I’m just missing the obvious. Help? You want to what? You want to execute an arbitrary system command and collect the command’s output? data = `command arg1 arg2 arg3` Obviously if the provided command line works in a shell, it will work here, and vice versa. ---
**Author:** ![twifkak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/a88e4f/32.png) [@twifkak](https://www.ruby-forum.com/u/twifkak)\ **Post date:** [November 29, 2006, 2:59pm UTC](https://www.ruby-forum.com/t/im-a-process-spawning-idiot/77625/3 "2006-11-29T14:59:15Z")
Eric H. wrote: > That said, try playing with shell.rb. I don’t really know what it > does, though. > Thanks! This Ruby program: STDOUT.reopen open(‘log.txt’,‘w’) exec ‘echo’, ‘Hi!’ **END** outputs “Hi!” to log.txt. shell.rb (or, more specifically, shell/process-controller.rb), uses this combined with fork (since exec replaces the process) to do its dirty work. Downloading win32-process now… 😃 Devin ---
**Author:** ![twifkak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/a88e4f/32.png) [@twifkak](https://www.ruby-forum.com/u/twifkak)\ **Post date:** [November 29, 2006, 9:00am UTC](https://www.ruby-forum.com/t/im-a-process-spawning-idiot/77625/4 "2006-11-29T09:00:27Z")
On Nov 28, 2006, at 2350 , Paul L. wrote: > > win32, unix, cygwin… > > and vice versa. > > system ‘command’, ‘arg with spaces’ will execute correctly (ARGV[0] > > will be ‘arg with spaces’) `command arg with spaces` requires manual intervention (ARGV[0] will be ‘arg’). That said, try playing with shell.rb. I don’t really know what it does, though. – Eric H. - removed\_email\_address@domain.invalid - [http://blog.segment7.net](http://blog.segment7.net) I LIT YOUR GEM ON FIRE! ---
**Author:** ![twifkak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/a88e4f/32.png) [@twifkak](https://www.ruby-forum.com/u/twifkak)\ **Post date:** [November 29, 2006, 3:41pm UTC](https://www.ruby-forum.com/t/im-a-process-spawning-idiot/77625/5 "2006-11-29T15:41:24Z")
For reference’s sake, I don’t need fork. The same trick works with Kernel#system. Some ugly code: inp, out = IO.pipe # start Thread.critical old\_stdout = STDOUT.dup STDOUT.reopen out system ‘echo’, ‘matz is nice!’ STDOUT.reopen old\_stdout # end Thread.critical out.close puts “Hey guess what: #{inp.read}” **END** Out of curiosity, is this one of those places where I’d _have_ to use Thread.critical (assuming I don’t want other threads putsing to my pipe)? Devin ---
**Author:** ![twifkak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/a88e4f/32.png) [@twifkak](https://www.ruby-forum.com/u/twifkak)\ **Post date:** [November 29, 2006, 3:45pm UTC](https://www.ruby-forum.com/t/im-a-process-spawning-idiot/77625/6 "2006-11-29T15:45:24Z")
On Wed, 29 Nov 2006, Devin M. wrote: > shell.rb (or, more specifically, shell/process-controller.rb), uses this > combined with fork (since exec replaces the process) to do its dirty work. > > Downloading win32-process now… 😃 > > Devin systemu.rb allows capture of stdout, stderr, and exit\_status and specification of stdin in an cross platform way. NAME systemu.rb SYNOPSIS univeral capture of stdout and stderr and handling of child process pid for windows, \*nix, etc. URIS [http://rubyforge.org/projects/codeforpeople/](http://rubyforge.org/projects/codeforpeople/) [http://codeforpeople.com/lib/ruby/](http://codeforpeople.com/lib/ruby/) INSTALL gem install systemu SAMPLES \<========\< samples/a.rb \>========\> ~ \> cat samples/a.rb ``` # # systemu can be used on any platform to return status, stdout, and ``` stderr of # any command. unlike other methods like open3/popen4 there is zero danger of # full pipes or threading issues hanging your process or subprocess. # require ‘systemu’ ``` date = %q( ruby -e" t = Time.now; STDOUT.puts t; STDERR.puts t ``` " ) ``` status, stdout, stderr = systemu date p [status, stdout, stderr] ``` ~ \> ruby samples/a.rb ``` [#, "Fri Nov 03 17:22:23 MST ``` 2006\n", “Fri Nov 03 17:22:23 MST 2006\n”] \<========\< samples/b.rb \>========\> ~ \> cat samples/b.rb ``` # # quite a few keys can be passed to the command to alter it's ``` behaviour. if # either stdout or stderr is supplied those objects should respond\_to? ‘\<\<’ # and only status will be returned # require ‘systemu’ ``` date = %q( ruby -e" t = Time.now; STDOUT.puts t; STDERR.puts t ``` " ) ``` stdout, stderr = '', '' status = systemu date, 'stdout' => stdout, 'stderr' => stderr p [status, stdout, stderr] ``` ~ \> ruby samples/b.rb ``` [#, "Fri Nov 03 17:22:23 MST ``` 2006\n", “Fri Nov 03 17:22:23 MST 2006\n”] \<========\< samples/c.rb \>========\> ~ \> cat samples/c.rb ``` # # of course stdin can be supplied too. synonyms for 'stdin' ``` include ‘0’ and # 0. the other stdio streams have similar shortcuts # require ‘systemu’ ``` cat = %q( ruby -e" ARGF.each{|line| puts line} " ) status = systemu cat, 0=>'the stdin for cat', 1=>stdout='' puts stdout ``` ~ \> ruby samples/c.rb ``` the stdin for cat ``` \<========\< samples/d.rb \>========\> ~ \> cat samples/d.rb ``` # # the cwd can be supplied # require 'systemu' require 'tmpdir' pwd = %q( ruby -e" STDERR.puts Dir.pwd " ) status = systemu pwd, 2=>(stderr=''), :cwd=>Dir.tmpdir puts stderr ``` ~ \> ruby samples/d.rb ``` /tmp ``` \<========\< samples/e.rb \>========\> ~ \> cat samples/e.rb ``` # # any environment vars specified are merged into the child's ``` environment # require ‘systemu’ ``` env = %q( ruby -r yaml -e" puts ENV['answer'] " ) status = systemu env, 1=>stdout='', 'env'=>{ 'answer' => 0b101010 ``` } puts stdout ~ \> ruby samples/e.rb ``` 42 ``` \<========\< samples/f.rb \>========\> ~ \> cat samples/f.rb ``` # # if a block is specified then it is passed the child pid and run ``` in a # background thread. note that this thread will **not** be blocked during the # execution of the command so it may do useful work such as killing the child # if execution time passes a certain threshold # require ‘systemu’ ``` looper = %q( ruby -e" loop{ STDERR.puts Time.now.to_i; sleep 1 } ``` " ) ``` status, stdout, stderr = systemu looper do |cid| sleep 3 Process.kill 9, cid end p [status, stdout, stderr] ``` ~ \> ruby samples/f.rb ``` [#, "", ``` “1162599744\n1162599745\n1162599746\n1162599747\n”] -a ---
**Author:** ![twifkak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/a88e4f/32.png) [@twifkak](https://www.ruby-forum.com/u/twifkak)\ **Post date:** [November 29, 2006, 3:53pm UTC](https://www.ruby-forum.com/t/im-a-process-spawning-idiot/77625/7 "2006-11-29T15:53:28Z")
On Wed, 29 Nov 2006, Devin M. wrote: > puts “Hey guess what: #{inp.read}” > **END** this is an insanely bad idea: a cross platform way to hang you system. try this: ``` harp:~ > cat a.rb big = 42.chr * 4242 inp, out = IO.pipe old_stdout = STDOUT.dup STDOUT.reopen out system 'echo', big STDOUT.reopen old_stdout harp:~ > ruby a.rb # hung process ``` you can’t keep writing to a pipe **unless** someone is guarunteed to be reading from the other end! make it easy on yourself: ``` harp:~ > cat a.rb require 'rubygems' require 'systemu' # gem install systemu systemu ['echo', 'matz is nice!'], :stdout=>STDOUT systemu ['echo', 'matz is nice!'], :stdout=>stdout='' p stdout systemu 'cat', :stdin=>['line1', 'line2'], :stdout=>stdout p stdout harp:~ > ruby a.rb matz is nice! "matz is nice!\n" "matz is nice!\nline1line2" ``` kind regards -a ---
**Author:** ![twifkak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/a88e4f/32.png) [@twifkak](https://www.ruby-forum.com/u/twifkak)\ **Post date:** [November 30, 2006, 2:50am UTC](https://www.ruby-forum.com/t/im-a-process-spawning-idiot/77625/8 "2006-11-30T02:50:12Z")
removed\_email\_address@domain.invalid wrote: > On Wed, 29 Nov 2006, Devin M. wrote: > > this is an insanely bad idea: a cross platform way to hang you system. > well, then. no need to be curt about it. 😛 > gem install systemu > aha! i had a stinking suspicion i should just’ve emailed you, and not > all of ruby-talk. thanks for the info, and the cool lib, ara. devin (tmp\_dir? Marshal.dump? Yikes. Glad I didn’t have to write that crap. Quick, someone put in an RCR for Kernel#backtick(cmd, \*args) so this craziness can go away.)