# I'm a process-spawning idiot **URL:** \ **Category:** ruby-talk\ **Created:** [29 November 2006 07:00 UTC](https://rubytalk.org/t/im-a-process-spawning-idiot/33300 "2006-11-29T07:00:21Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Devin\_Mullins](https://avatars.discourse-cdn.com/v4/letter/d/958977/32.png) [@Devin\_Mullins](https://rubytalk.org/u/Devin_Mullins)\ **Post date:** [29 November 2006 07:00 UTC](https://rubytalk.org/t/im-a-process-spawning-idiot/33300/1 "2006-11-29T07:00:21Z")
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:** ![Paul\_Lutus](https://avatars.discourse-cdn.com/v4/letter/p/2bfe46/32.png) [@Paul\_Lutus](https://rubytalk.org/u/Paul_Lutus)\ **Post date:** [29 November 2006 07:50 UTC](https://rubytalk.org/t/im-a-process-spawning-idiot/33300/2 "2006-11-29T07:50:05Z")
Devin Mullins 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. > **···** > > -- > Paul Lutus > [http://www.arachnoid.com](http://www.arachnoid.com) ---
**Author:** ![Eric\_Hodel1](https://avatars.discourse-cdn.com/v4/letter/e/a9adbd/32.png) [@Eric\_Hodel1](https://rubytalk.org/u/Eric_Hodel1)\ **Post date:** [29 November 2006 07:58 UTC](https://rubytalk.org/t/im-a-process-spawning-idiot/33300/3 "2006-11-29T07:58:22Z")
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. > **···** > > On Nov 28, 2006, at 2350 , Paul Lutus wrote: > > > Devin Mullins 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. > > -- > Eric Hodel - drbrain@segment7.net - [http://blog.segment7.net](http://blog.segment7.net) > > I LIT YOUR GEM ON FIRE! ---
**Author:** ![Devin\_Mullins](https://avatars.discourse-cdn.com/v4/letter/d/958977/32.png) [@Devin\_Mullins](https://rubytalk.org/u/Devin_Mullins)\ **Post date:** [29 November 2006 13:57 UTC](https://rubytalk.org/t/im-a-process-spawning-idiot/33300/4 "2006-11-29T13:57:40Z")
Eric Hodel 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:** ![Devin\_Mullins](https://avatars.discourse-cdn.com/v4/letter/d/958977/32.png) [@Devin\_Mullins](https://rubytalk.org/u/Devin_Mullins)\ **Post date:** [29 November 2006 14:40 UTC](https://rubytalk.org/t/im-a-process-spawning-idiot/33300/5 "2006-11-29T14:40:12Z")
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 Devin Mullins wrote: > **···** > > > 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... 😃 ---
**Author:** ![Ara.T.Howard6](https://avatars.discourse-cdn.com/v4/letter/a/958977/32.png) [@Ara.T.Howard6](https://rubytalk.org/u/Ara.T.Howard6)\ **Post date:** [29 November 2006 14:44 UTC](https://rubytalk.org/t/im-a-process-spawning-idiot/33300/6 "2006-11-29T14:44:36Z")
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 > **···** > > On Wed, 29 Nov 2006, Devin Mullins wrote: > > > Eric Hodel 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 > >      # >      # 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 > -- > if you want others to be happy, practice compassion. > if you want to be happy, practice compassion. -- the dalai lama ---
**Author:** ![Ara.T.Howard6](https://avatars.discourse-cdn.com/v4/letter/a/958977/32.png) [@Ara.T.Howard6](https://rubytalk.org/u/Ara.T.Howard6)\ **Post date:** [29 November 2006 14:52 UTC](https://rubytalk.org/t/im-a-process-spawning-idiot/33300/7 "2006-11-29T14:52:40Z")
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 > **···** > > On Wed, 29 Nov 2006, Devin Mullins wrote: > > > 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\_\_ > > -- > if you want others to be happy, practice compassion. > if you want to be happy, practice compassion. -- the dalai lama ---
**Author:** ![Devin\_Mullins](https://avatars.discourse-cdn.com/v4/letter/d/958977/32.png) [@Devin\_Mullins](https://rubytalk.org/u/Devin_Mullins)\ **Post date:** [30 November 2006 01:49 UTC](https://rubytalk.org/t/im-a-process-spawning-idiot/33300/8 "2006-11-30T01:49:46Z")
> \ > 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.) > **···** > > ara.t.howard@noaa.gov wrote: > > > On Wed, 29 Nov 2006, Devin Mullins wrote: