# Open4-0.3.0

**URL:** <https://www.ruby-forum.com/t/open4-0-3-0/94047>\
**Category:** Ruby\
**Created:** [April 19, 2006, 4:53am UTC](https://www.ruby-forum.com/t/open4-0-3-0/94047 "2006-04-19T04:53:34Z")\
**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:** [April 19, 2006, 4:53am UTC](https://www.ruby-forum.com/t/open4-0-3-0/94047/1 "2006-04-19T04:53:34Z")

</div>

URIS

[http://rubyforge.org/frs/?group\_id=1024](http://rubyforge.org/frs/?group_id=1024)  
[http://www.codeforpeople.com/lib/ruby/](http://www.codeforpeople.com/lib/ruby/)

SYNOPSIS

open child process with handles on pid, stdin, stdout, and stderr

HISTORY

0.3.0 :  
- bug fix from jordan breeding. general clean up. added spawn  
method.

0.2.0 :  
- added exception marshaled from child → parent when exec fails.  
thanks  
to jordan breeding for a patch (yay!) and paul brannan for this  
most  
excellent idea.

0.1.0 :  
- fixed docs to correctly show return value of popen4 (pid first  
not last).  
thanks Stefanie T. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) for catching this.  
0.0.0 :  
- initial version

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"
 ""

```

AUTHOR

removed\_email\_address@domain.invalid

LICENSE

ruby’s

enjoy.

-a