# Open4-0.9.2

**URL:** <https://www.ruby-forum.com/t/open4-0-9-2/90122>\
**Category:** Ruby\
**Created:** [March 26, 2007, 7:18am UTC](https://www.ruby-forum.com/t/open4-0-9-2/90122 "2007-03-26T07:18:56Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\
**Post date:** [March 26, 2007, 7:18am UTC](https://www.ruby-forum.com/t/open4-0-9-2/90122/1 "2007-03-26T07:18:56Z")

</div>

URIS

[http://rubyforge.org/projects/codeforpeople/](http://rubyforge.org/projects/codeforpeople/)  
[http://www.codeforpeople.com/lib/ruby/](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

0.9.2:  
- fixed a descriptor leak. thanks Andre N…

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

removed\_email\_address@domain.invalid

LICENSE

ruby’s

-a