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Random thoughts, bright ideas and interesting experiments. In short the ramblings of a fulltime nerd.


SystemProcess - Execute System Commands with Ease

Jakob Westhoff

A current project of mine demanded me to invoke a lot of different programms on the commandline. Some calls were simple executions of a command followed by one or two arguments. Others were more complex with the need to define special environment variables or custom file descriptors. Some of them even needed me to asyncronously run the programs to be able to read their output during execution or run multiple commands at once. Because nobody, includind me, really likes the proc_* family of functions like proc_open in php, I decided to write a simple and yet powerful object oriented wrapper around all this functionality. The wrapper is fully unit tested and licensed under LGPLv3 for you to use in your projects.


The wrapper currently has the following features:

  • Automagically escaping of commands and arguments
  • Redirecting stdout/stderr output
  • Create multiple commands and pipe their output to each other
  • Set custom environment variables
  • Set a custom working directory
  • Provide custom stdin data
  • Use an arbitrary amount of custom file descriptors
  • Execute commands syncronously or asyncronously
  • Send signals to running processes

This is are all currently supported features. I think nearly all of the usecases of invoking an external command are covered by these. If there is any functionality or feature I have not yet thought of, please drop me a line and I will be happy to add it.

Further information and examples

SystemProcess was designed having great flexibility combined with a maximum amount of comfort in mind. The fluent interface pattern is used to provide an easy and readable way of defining complex commandstrings as well as simple ones. There is no need to handle the escaping of your arguments as this will be done automatically.

The constructor takes the executable to run as an argument. The following example will execute the command "echo" with the two arguments "foo" and "bar":

<?php data-preserve-html-node="true"
  $p = new pbsSystemProcess( 'echo' );
  $p->argument( 'foo' )->argument( 'bar' );
  $returnCode = $p->execute();

As you can see the fluent interface is used to combine the argument calls in a readable way.

Quite complex constructs containing redirects, pipes or even custom file descriptors are possible too. They can be realized with nearly no effort:

<?php data-preserve-html-node="true"
  $consumer  = new pbsSystemProcess( 'cat' );
  $consumer->redirect( pbsSystemProcess::STDOUT, pbsSystemProcess::STDERR );

  $provider  = new pbsSystemProcess( 'echo' );
  $provider->nonZeroExitCodeException = true;
  $provider->argument( 'foobar' )
           ->pipe( $consumer )

  var_dump( $provider->stderrOutput );

As you can see even complex commands are still quite readable. If the attribute "nonZeroExitCodeException" is set to true an exception will be thrown instead of just returning a non zero exit code. This exception will contain the stdout- and stderrOutput as well as the executed command string.

In case you need asyncronous execution call the execute function with the first argument set to "true". You will get a set of pipes in return which you can work with like any other stream in php.

If you just want to use this classes api to generate the shell commands, but do have no intention to actually execute it you can use the __toString() functionallity of SystemProcess. An explicit conversion of this object to string will give you the string context as well, as a use in any string context like printf. :

<?php data-preserve-html-node="true"
  $p = new pbsSystemProcess( 'echo' );
  $p->argument( 'foo' )
    ->argument( 'bar' )

  // Store command to a variable
  $command = (string)$p;
  // Or print it out
  echo $p, "\n";

For the more advanced functionallity like sending signals to running processes take a look at the api documentation, which is well structured und quite complete.


You can obtain SystemProcess from its svn repository which can be found at:


If you have the subversion client installed on your system you can use the following command to get a copy of the most recent SystemProcess version:

svn co svn:// systemProcess

Feature requests and bug reports

Currently there is not bug reporting tool available for this project. If you have got a feature request or a bug report please use the comment function of this blog or send me an email and I will see what I can do to make SystemProcess even better.