PHP HTML CSS Tutorials

It happens pretty often for me to have to run shell commands in a hosting environment. I do it all the time via a simple php script. I tested it on godaddy and dreamhost and on other hostings environments and it works fine.

Before starting the tutorial you should note that if this script is not handled carefully it can have undesired results. A wrong rm command can delete all the files you have on your hosting, so run the commands with care.

Running Shell Commands from PHP

In the first part of this tutorial we are going to see how we can run a shell command from php and how to retrieve the command ouput. The php function which is responsible to run a shell command is proc_open.

The proc_open function accepts a couple of parameters:

resource proc_open ( string $cmd
                           , array $descriptorspec
                           , array &$pipes
                         [, string $cwd
                         [, array $env
                         [, array $other_options ]]] )

We are going to use the first 3 parameters:

• cmd – the command to execute. The command string will contain the full command as we would write in the shell command line, including the input parameters.
• descriptorspec – is an indexed array containing the description of the pipes. The first element should contain the input pipe, the second one should contain the output pipe and the third one the stderr(the pipe where the command will return the error it encounter). Each one can be one of the types “pipe” of “file”
• pipes – is another indexed array that contains the reference to the pipes that are created during process. For example if in the descriptorsspec is specified a pipe for the input, the pipe array will contain the input pipe, which can be used to write to the input stream. The same can happen with the output stream: a pipe can be used to take the output of the command.

  If a pipe is not used, a file can be used instead. Usually temporary files are used. In our example we are going to use a pipe for the input and tmp files for the output and for the stderr. Because we don’t need to pass any input file to the command we are going to close the input pipe immediately, without writing anything in it.

The proc_open function will be run slightly different on windows and linux environments. Windows processes don’t return a stderr, so it can not be used to test the success of a command on and windows environment.

Here is the function we are going to use to run a command:

function cmd_exec($cmd, &$stdout, &$stderr)
{
   $outfile = tempnam(".", "cmd");
   $errfile = tempnam(".", "cmd");
   $descriptorspec = array(
       0 => array("pipe", "r"),
       1 => array("file", $outfile, "w"),
       2 => array("file", $errfile, "w")
   );
   $proc = proc_open($cmd, $descriptorspec, $pipes);

   if (!is_resource($proc)) return 255;

   fclose($pipes[0]);    //Don't really want to give any input

   $exit = proc_close($proc);
   $stdout = file($outfile);
   $stderr = file($errfile);

   unlink($outfile);
   unlink($errfile);
   return $exit;
}

Adding a Form

Now that we wrote the function to run a shell command from php, we need to write a html form from where to trigger the execution of the shell commands. First we define an html form:

Command:



		

And finally we add the code to run the command entered in the form:

if (isset($_POST['command']))
{
	echo 'Command: ' . $_POST['command'] . '';
	$exit = cmd_exec($_POST['command'],$stdout, $stderr);

	//print the output
	foreach ($stdout as $line)
	{
		echo "$line";
	}

	//in case there an error is returned
	foreach ($stderr as $line)
	{
		echo "$line";
	}
}

Now all you have to do is to put all the snippets described above in a php file. Of you can download it from here. You have to use with caution and keep in mind that it is not protected by password. In the next tutorial we are going to ad a login form to the script.