The Process Component

Installation¶

You can install the component in 2 different ways:

• Install it via Composer (symfony/process on Packagist);
• Use the official Git repository (https://github.com/symfony/Process).

Usage¶

The Process class allows you to execute a command in a sub-process:

use SymfonyComponentProcessProcess;

$process = new Process('ls -lsa');
$process->run();

// executes after the command finishes
if (!$process->isSuccessful()) {
    throw new RuntimeException($process->getErrorOutput());
}

echo $process->getOutput();

The component takes care of the subtle differences between the different platforms when executing the command.

The getOutput() method always return the whole content of the standard output of the command and getErrorOutput() the content of the error output. Alternatively, the getIncrementalOutput() and getIncrementalErrorOutput() methods returns the new outputs since the last call.

The clearOutput() method clears the contents of the output and clearErrorOutput() clears the contents of the error output.

The mustRun() method is identical to run(), except that it will throw a ProcessFailedException if the process couldn’t be executed successfully (i.e. the process exited with a non-zero code):

use SymfonyComponentProcessExceptionProcessFailedException;
use SymfonyComponentProcessProcess;

$process = new Process('ls -lsa');

try {
    $process->mustRun();

    echo $process->getOutput();
} catch (ProcessFailedException $e) {
    echo $e->getMessage();
}

Getting real-time Process Output¶

When executing a long running command (like rsync-ing files to a remote server), you can give feedback to the end user in real-time by passing an anonymous function to the run() method:

use SymfonyComponentProcessProcess;

$process = new Process('ls -lsa');
$process->run(function ($type, $buffer) {
    if (Process::ERR === $type) {
        echo 'ERR > '.$buffer;
    } else {
        echo 'OUT > '.$buffer;
    }
});

Running Processes Asynchronously¶

You can also start the subprocess and then let it run asynchronously, retrieving output and the status in your main process whenever you need it. Use the start() method to start an asynchronous process, the isRunning() method to check if the process is done and the getOutput() method to get the output:

$process = new Process('ls -lsa');
$process->start();

while ($process->isRunning()) {
    // waiting for process to finish
}

echo $process->getOutput();

You can also wait for a process to end if you started it asynchronously and are done doing other stuff:

$process = new Process('ls -lsa');
$process->start();

// ... do other things

$process->wait(function ($type, $buffer) {
    if (Process::ERR === $type) {
        echo 'ERR > '.$buffer;
    } else {
        echo 'OUT > '.$buffer;
    }
});

Stopping a Process¶

Any asynchronous process can be stopped at any time with the stop() method. This method takes two arguments: a timeout and a signal. Once the timeout is reached, the signal is sent to the running process. The default signal sent to a process is SIGKILL. Please read the signal documentation below to find out more about signal handling in the Process component:

$process = new Process('ls -lsa');
$process->start();

// ... do other things

$process->stop(3, SIGINT);

Executing PHP Code in Isolation¶

If you want to execute some PHP code in isolation, use the PhpProcess instead:

use SymfonyComponentProcessPhpProcess;

$process = new PhpProcess(<<<EOF
    <?php echo 'Hello World'; ?>
EOF
);
$process->run();

To make your code work better on all platforms, you might want to use the ProcessBuilder class instead:

use SymfonyComponentProcessProcessBuilder;

$builder = new ProcessBuilder(array('ls', '-lsa'));
$builder->getProcess()->run();

In case you are building a binary driver, you can use the setPrefix() method to prefix all the generated process commands.

The following example will generate two process commands for a tar binary adapter:

use SymfonyComponentProcessProcessBuilder;

$builder = new ProcessBuilder();
$builder->setPrefix('/usr/bin/tar');

// '/usr/bin/tar' '--list' '--file=archive.tar.gz'
echo $builder
    ->setArguments(array('--list', '--file=archive.tar.gz'))
    ->getProcess()
    ->getCommandLine();

// '/usr/bin/tar' '-xzf' 'archive.tar.gz'
echo $builder
    ->setArguments(array('-xzf', 'archive.tar.gz'))
    ->getProcess()
    ->getCommandLine();

Process Timeout¶

You can limit the amount of time a process takes to complete by setting a timeout (in seconds):

use SymfonyComponentProcessProcess;

$process = new Process('ls -lsa');
$process->setTimeout(3600);
$process->run();

If the timeout is reached, a RuntimeException is thrown.

For long running commands, it is your responsibility to perform the timeout check regularly:

$process->setTimeout(3600);
$process->start();

while ($condition) {
    // ...

    // check if the timeout is reached
    $process->checkTimeout();

    usleep(200000);
}

Process Idle Timeout¶

In contrast to the timeout of the previous paragraph, the idle timeout only considers the time since the last output was produced by the process:

use SymfonyComponentProcessProcess;

$process = new Process('something-with-variable-runtime');
$process->setTimeout(3600);
$process->setIdleTimeout(60);
$process->run();

In the case above, a process is considered timed out, when either the total runtime exceeds 3600 seconds, or the process does not produce any output for 60 seconds.

Process Signals¶

When running a program asynchronously, you can send it POSIX signals with the signal() method:

use SymfonyComponentProcessProcess;

$process = new Process('find / -name "rabbit"');
$process->start();

// will send a SIGKILL to the process
$process->signal(SIGKILL);

Process Pid¶

You can access the pid of a running process with the getPid() method.

use SymfonyComponentProcessProcess;

$process = new Process('/usr/bin/php worker.php');
$process->start();

$pid = $process->getPid();

Disabling Output¶

As standard output and error output are always fetched from the underlying process, it might be convenient to disable output in some cases to save memory. Use disableOutput() and enableOutput() to toggle this feature:

use SymfonyComponentProcessProcess;

$process = new Process('/usr/bin/php worker.php');
$process->disableOutput();
$process->run();