URIS

   http://rubyforge.org/projects/codeforpeople/
   http://www.codeforpeople.com/lib/ruby/

SYNOPSIS

   open child process with handles on pid, stdin, stdout, and stderr: manage
   child processes and their io handles easily.

HISTORY

   0.8.0:

     - fixed a critical bug whereby a process producing tons of stdout, but for
       which the stdout was not handled, would cause the child process to
       become blocked/hung writing to the pipe.  eg, this command would cause a
       hang

         include Open4

         spawn 'ruby -e"  puts Array.new(65536){ 42 }  "'

       whereas this one would not

         include Open4

         spawn 'ruby -e"  puts Array.new(65536){ 42 }  "', :stdout=>StringIO.new

       this version handles the former by spawning a 'null' thread which reads,
       but does not process stdout/stderr.  that way commands which generate
       tons of output will never become blocked.


INSTALL

   ~> gem install open4

SAMPLES

   ----------------------------------------------------------------------------
   simple usage
   ----------------------------------------------------------------------------

     harp: > cat sample/simple.rb
     require "open4"

     pid, stdin, stdout, stderr = Open4::popen4 "sh"

     stdin.puts "echo 42.out"
     stdin.puts "echo 42.err 1>&2"
     stdin.close

     ignored, status = Process::waitpid2 pid

     puts "pid        : #{ pid }"
     puts "stdout     : #{ stdout.read.strip }"
     puts "stderr     : #{ stderr.read.strip }"
     puts "status     : #{ status.inspect }"
     puts "exitstatus : #{ status.exitstatus }"


     harp: > ruby sample/simple.rb
     pid        : 17273
     stdout     : 42.out
     stderr     : 42.err
     status     : #<Process::Status: pid=17273,exited(0)>
     exitstatus : 0


   ----------------------------------------------------------------------------
   in block form - the child process is automatically waited for
   ----------------------------------------------------------------------------

     harp: > cat sample/block.rb
     require 'open4'

     status =
       Open4::popen4("sh") do |pid, stdin, stdout, stderr|
         stdin.puts "echo 42.out"
         stdin.puts "echo 42.err 1>&2"
         stdin.close

         puts "pid        : #{ pid }"
         puts "stdout     : #{ stdout.read.strip }"
         puts "stderr     : #{ stderr.read.strip }"
       end

         puts "status     : #{ status.inspect }"
         puts "exitstatus : #{ status.exitstatus }"


     harp: > ruby sample/block.rb
     pid        : 17295
     stdout     : 42.out
     stderr     : 42.err
     status     : #<Process::Status: pid=17295,exited(0)>
     exitstatus : 0

   ----------------------------------------------------------------------------
   exceptions are marshaled from child to parent if fork/exec fails
   ----------------------------------------------------------------------------

     harp: > cat sample/exception.rb
     require "open4"
     Open4::popen4 "noexist"


     harp: > ruby sample/exception.rb
     /dmsp/reference/ruby-1.8.1//lib/ruby/site_ruby/open4.rb:100:in `popen4': No such file or directory - noexist (Errno::ENOENT)
             from sample/exception.rb:3

   ----------------------------------------------------------------------------
   the spawn method provides and even more convenient method of running a
   process, allowing any object that supports 'each', 'read', or 'to_s' to be
   given as stdin and any objects that support '<<' to be given as
   stdout/stderr.  an exception is thrown if the exec'd cmd fails (nonzero
   exitstatus) unless the option 'raise'=>false is given
   ----------------------------------------------------------------------------

     harp: > cat sample/spawn.rb
     require 'open4'
     include Open4

     cat = '  ruby -e"  ARGF.each{|line| STDOUT << line}  "  '

     stdout, stderr = '', ''
     status = spawn cat, 'stdin' => '42', 'stdout' => stdout, 'stderr' => stderr
     p status
     p stdout
     p stderr

     stdout, stderr = '', ''
     status = spawn cat, 0=>'42', 1=>stdout, 2=>stderr
     p status
     p stdout
     p stderr


     harp: > RUBYLIB=lib ruby sample/spawn.rb
     0
     "42"
     ""
     0
     "42"
     ""


   ----------------------------------------------------------------------------
   the bg/background method is similar to spawn, but the process is
   automatically set running in a thread.  the returned thread has several
   methods added dynamically which return the pid and blocking calls to the
   exitstatus.
   ----------------------------------------------------------------------------

     harp: > cat sample/bg.rb
     require 'yaml'
     require 'open4'
     include Open4

     stdin = '42'
     stdout = ''
     stderr = ''

     t = bg 'ruby -e"sleep 4; puts ARGF.read"', 0=>stdin, 1=>stdout, 2=>stderr

     waiter = Thread.new{ y t.pid => t.exitstatus } # t.exitstatus is a blocking call!

     while((status = t.status))
       y "status" => status
       sleep 1
     end

     waiter.join

     y "stdout" => stdout


     harp: > ruby sample/bg.rb
     ---
     status: run
     ---
     status: sleep
     ---
     status: sleep
     ---
     status: sleep
     ---
     21357: 0
     ---
     stdout: "42\n"

   ----------------------------------------------------------------------------
   the timeout methods can be used to ensure execution is preceding at the
   desired interval.  note also how to setup a 'pipeline'
   ----------------------------------------------------------------------------

     harp: > cat sample/stdin_timeout.rb
     require 'open4'

     producer = 'ruby -e" STDOUT.sync = true; loop{sleep(rand+rand) and puts 42} "'

     consumer = 'ruby -e" STDOUT.sync = true; STDIN.each{|line| puts line} "'

     open4(producer) do |pid, i, o, e|

       open4.spawn consumer, :stdin=>o, :stdout=>STDOUT, :stdin_timeout => 1.4

     end


     harp: > ruby sample/stdin_timeout.rb
     42
     42
     42
     42
     42
     /dmsp/reference/ruby-1.8.1//lib/ruby/1.8/timeout.rb:42:in `relay': execution expired (Timeout::Error)

AUTHOR

   ara.t.howard / noaa.gov

LICENSE

   ruby's

-a
-- 
in order to be effective truth must penetrate like an arrow - and that is
likely to hurt. -- wei wu wei