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.. index::
   single: Process
   single: Components; Process

The Process Component

The Process component executes commands in sub-processes.

Installation

You can install the component in 2 different ways:

Usage

The :class:`Symfony\\Component\\Process\\Process` class allows you to execute a command in a sub-process:

use Symfony\Component\Process\Process;
use Symfony\Component\Process\Exception\ProcessFailedException;

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

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

echo $process->getOutput();

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

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

The :method:`Symfony\\Component\\Process\\Process::clearOutput` method clears the contents of the output and :method:`Symfony\\Component\\Process\\Process::clearErrorOutput` clears the contents of the error output.

The mustRun() method is identical to run(), except that it will throw a :class:`Symfony\\Component\\Process\\Exception\\ProcessFailedException` if the process couldn't be executed successfully (i.e. the process exited with a non-zero code):

use Symfony\Component\Process\Exception\ProcessFailedException;
use Symfony\Component\Process\Process;

$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 :method:`Symfony\\Component\\Process\\Process::run` method:

use Symfony\Component\Process\Process;

$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 :method:`Symfony\\Component\\Process\\Process::start` method to start an asynchronous process, the :method:`Symfony\\Component\\Process\\Process::isRunning` method to check if the process is done and the :method:`Symfony\\Component\\Process\\Process::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();

// ... do things after the process has finished

Note

The :method:`Symfony\\Component\\Process\\Process::wait` method is blocking, which means that your code will halt at this line until the external process is completed.

Note

If a Response is sent before a child process had a chance to complete, the server process will be killed (depending on your OS). It means that your task will be stopped right away. Running an asynchronous process is not the same as running a process that survives its parent process.

If you want your process to survive the request/response cycle, you can take advantage of the kernel.terminate event, and run your command synchronously inside this event. Be aware that kernel.terminate is called only if you use PHP-FPM.

Caution!

Beware also that if you do that, the said PHP-FPM process will not be available to serve any new request until the subprocess is finished. This means you can quickly block your FPM pool if you're not careful enough. That is why it's generally way better not to do any fancy things even after the request is sent, but to use a job queue instead.

:method:`Symfony\\Component\\Process\\Process::wait` takes one optional argument: a callback that is called repeatedly whilst the process is still running, passing in the output and its type:

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

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

Stopping a Process

.. versionadded:: 2.3
    The ``signal`` parameter of the ``stop()`` method was introduced in Symfony 2.3.

Any asynchronous process can be stopped at any time with the :method:`Symfony\\Component\\Process\\Process::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 :ref:`signal documentation below<reference-process-signal>` 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 Symfony\Component\Process\PhpProcess;

$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 :class:`Symfony\\Component\\Process\\ProcessBuilder` class instead:

use Symfony\Component\Process\ProcessBuilder;

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

.. versionadded:: 2.3
    The :method:`ProcessBuilder::setPrefix<Symfony\\Component\\Process\\ProcessBuilder::setPrefix>`
    method was introduced in Symfony 2.3.

In case you are building a binary driver, you can use the :method:`Symfony\\Component\\Process\\ProcessBuilder::setPrefix` method to prefix all the generated process commands.

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

use Symfony\Component\Process\ProcessBuilder;

$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 Symfony\Component\Process\Process;

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

If the timeout is reached, a :class:`Symfony\\Component\\Process\\Exception\\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 Symfony\Component\Process\Process;

$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

.. versionadded:: 2.3
    The ``signal()`` method was introduced in Symfony 2.3.

When running a program asynchronously, you can send it POSIX signals with the :method:`Symfony\\Component\\Process\\Process::signal` method:

use Symfony\Component\Process\Process;

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

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

Caution!

Due to some limitations in PHP, if you're using signals with the Process component, you may have to prefix your commands with exec. Please read Symfony Issue#5759 and PHP Bug#39992 to understand why this is happening.

POSIX signals are not available on Windows platforms, please refer to the PHP documentation for available signals.

Process Pid

.. versionadded:: 2.3
    The ``getPid()`` method was introduced in Symfony 2.3.

You can access the pid of a running process with the :method:`Symfony\\Component\\Process\\Process::getPid` method.

use Symfony\Component\Process\Process;

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

$pid = $process->getPid();

Caution!

Due to some limitations in PHP, if you want to get the pid of a symfony Process, you may have to prefix your commands with exec. Please read Symfony Issue#5759 to understand why this is happening.

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 :method:`Symfony\\Component\\Process\\Process::disableOutput` and :method:`Symfony\\Component\\Process\\Process::enableOutput` to toggle this feature:

use Symfony\Component\Process\Process;

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

Caution!

You cannot enable or disable the output while the process is running.

If you disable the output, you cannot access getOutput(), getIncrementalOutput(), getErrorOutput() or getIncrementalErrorOutput(). Moreover, you could not pass a callback to the start(), run() or mustRun() methods or use setIdleTimeout().