The Process Component
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The Process Component
The Process component executes commands in sub-processes.
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).
Then, require the vendor/autoload.php
file to enable the autoloading mechanism
provided by Composer. Otherwise, your application won't be able to find the classes
of this Symfony component.
Usage
The Process class allows you to execute a command in a sub-process:
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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 getIncrementalOutput()
and getIncrementalErrorOutput()
methods return the new output 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):
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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 run() method:
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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 > '.$buffer;
}
});
Running Processes Asynchronously
You can also start the subprocess and then let it run asynchronously, retrieving output and the status in your main process whenever you need it. Use the start() method to start an asynchronous process, the isRunning() method to check if the process is done and the getOutput() method to get the output:
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$process = new Process('ls -lsa');
$process->start();
while ($process->isRunning()) {
// waiting for process to finish
}
echo $process->getOutput();
You can also wait for a process to end if you started it asynchronously and are done doing other stuff:
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$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 > '.$buffer;
}
});
Note
The wait() method is blocking, which means that your code will halt at this line until the external process is completed.
Stopping a Process
Any asynchronous process can be stopped at any time with the
stop() method. This method takes
two arguments: a timeout and a signal. Once the timeout is reached, the signal
is sent to the running process. The default signal sent to a process is SIGKILL
.
Please read the signal documentation below
to find out more about signal handling in the Process component:
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$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:
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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 ProcessBuilder class instead:
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use Symfony\Component\Process\ProcessBuilder;
$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:
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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):
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use Symfony\Component\Process\Process;
$process = new Process('ls -lsa');
$process->setTimeout(3600);
$process->run();
If the timeout is reached, a RuntimeException is thrown.
For long running commands, it is your responsibility to perform the timeout check regularly:
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$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:
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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
When running a program asynchronously, you can send it POSIX signals with the signal() method:
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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
You can access the pid of a running process with the getPid() method.
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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 disableOutput() and enableOutput() to toggle this feature:
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use Symfony\Component\Process\Process;
$process = new Process('/usr/bin/php worker.php');
$process->disableOutput();
$process->run();
Caution
You can not 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
.