PHP Execute shell command asynchronously and retrieve live output

Question

I'd like to execute a shell command asynchronously in PHP. I.e. PHP shouldn't wait for the command to be finished to continue execution. However in contrast to the numerous question about that topic on Stackoverflow I do care about the output of the program. In particular I would like to do something like this:

exec("some command", $output_array, $has_finished);
while(count($output_array) > 0 && !$has_finished)
{
    if(count($output_array) > 0)
    {
        $line = array_shift($output_array);
        do_something_with_that($line);
    } else
        sleep(1);
}

do_something_with_that($line)
{
    echo $line."\n";
    flush();
}

The above code would work if exec would return immediately while still adding elements to the array and if there was a method to check if the process has terminated or not.

Is there a way to do that?

You can spawn a thread that does that and check the status of that thread. There's probably lots of resources that you can check. However you can't do this with native PHP and will need a module or library. — apokryfos
– apokryfos, Commented Feb 14, 2017 at 10:55
@apokryfos proc_open is a very native PHP function. Libs just make it a bit more convenient to to work with it. — Alex Blex
– Alex Blex, Commented Feb 14, 2017 at 13:29

Scindix · Accepted Answer · 2017-02-24 08:09:33Z

I've solved the problem by piping the output STDIN to a temporary file and then reading from it.

Here's my

Implementation

class ExecAsync {

    public function __construct($cmd) {
        $this->cmd = $cmd;
        $this->cacheFile = ".cache-pipe-".uniqid();
        $this->lineNumber = 0;
    }

    public function getLine() {
        $file = new SplFileObject($this->cacheFile);
        $file->seek($this->lineNumber);
        if($file->valid())
        {
            $this->lineNumber++;
            $current = $file->current();
            return $current;
        } else
            return NULL;
    }

    public function hasFinished() {
        if(file_exists(".status-".$this->cacheFile) ||
            (!file_exists(".status-".$this->cacheFile) && !file_exists($this->cacheFile)))
        {
            unlink($this->cacheFile);
            unlink(".status-".$this->cacheFile);
            $this->lineNumber = 0;
            return TRUE;
        } else
            return FALSE;
    }

    public function run() {
        if($this->cmd) {
            $out = exec('{ '.$this->cmd." > ".$this->cacheFile." && echo finished > .status-".$this->cacheFile.";} > /dev/null 2>/dev/null &");
        }
    }
}

Usage

$command = new ExecAsync("command to execute");
//run the command
$command->run();
/*We want to read from the command output as long as
 *there are still lines left to read
 *and the command hasn't finished yet

 *if getLine returns NULL it means that we have caught up
 *and there are no more lines left to read
 */
while(($line = $command->getLine()) || !$command->hasFinished())
{
    if($line !== NULL)
    {
        echo $line."\n";
        flush();
    } else
    {
        usleep(10);
    }
}

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