On Tue, 2 Jan 2007, Robert James wrote:

> What's the best way to see if a particular platform supports fork?  I
> know I could check if it's running on Windows, but I'd like something
> more direct (and presumably accurate).

has_fork =
   begin
     fork{ exit }
     Process.wait
     true
   rescue
     false
   end

>
> A similar question: assuming a standard Ruby install (that is, no
> popen4), what's the most robust way of running a shell command and
> capturing STDOUT and STDERR?
> `command 2>&1` seems to not always work on Windows.
>

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://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

     [#<Process::Status: pid=9960,exited(0)>, "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

     [#<Process::Status: pid=9965,exited(0)>, "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

     [#<Process::Status: pid=9985,signaled(SIGKILL=9)>, "", "1162599744\n1162599745\n1162599746\n1162599747\n"]



-a
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if you find yourself slandering anybody, first imagine that your mouth is
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dalai lama