Is there a way to use shell_exec without waiting for the command to complete?

Question

I have a process intensive task that I would like to run in the background.

The user clicks on a page, the PHP script runs, and finally, based on some conditions, if required, then it has to run a shell script, E.G.:

shell_exec('php measurePerformance.php 47 844 email@yahoo.com');

Currently I use shell_exec, but this requires the script to wait for an output. Is there any way to execute the command I want without waiting for it to complete?

NOTE: The process has to start immediately so a cron is not an option. — ToughPal, Jun 19 '09 at 20:27
Just a quick note: Make sure the page will not be accessible by everyone (search engines/ fraudulent users) and if you are on a shared environment, the execution time of all your scripts (in particular php!) probably is limited. In any case you may want to take a look at set_time_limit/php.ini. — merkuro, Jun 19 '09 at 20:35
Possible duplicate of [php execute a background process](https://stackoverflow.com/questions/45953/php-execute-a-background-process) — Sean the Bean, Jan 31 '18 at 21:33

score 152 · Accepted Answer · answered Jun 19 '09 at 20:27

152

How about adding.

"> /dev/null 2>/dev/null &"

shell_exec('php measurePerformance.php 47 844 email@yahoo.com > /dev/null 2>/dev/null &');

Note this also gets rid of the stdio and stderr.

answered Jun 19 '09 at 20:27

jitter

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It works perfectly. Are there any problems / side effects of using this?? – ToughPal Jun 19 '09 at 20:39
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No. No side effects. If you sometime decide you want the stdio or stderr output of your process consider http://stackoverflow.com/questions/45953/php-execute-a-background-process/45966#45966 – jitter Jun 19 '09 at 21:00
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Question: That's just discarding the output, right? Does PHP still wait for the process to finish before continuing execution, or does it fire and forget? – Alan Storm Jun 19 '09 at 21:06
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Yes discards out. Yes fire and forget – jitter Jun 19 '09 at 21:17
Works like a charm! Thanks! – buzznfrog Jan 15 '13 at 14:03
it is not working for the following is there any mistake I did? shell_exec('ffmpeg -f dshow -i video="Logitech HD Pro Webcam C920":audio="Rear Input (SoundMAX Integrated" -vcodec libx264 -b:v 600k -b:a 128k -f flv rtmp://127.0.0.1/live/mystream > /dev/null 2>/dev/null &'); – Thirumalai murugan Feb 26 '13 at 13:39
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Note: `> /dev/null 2>&1 &` as seen in other answers is a terse form of `> /dev/null 2>/dev/null &` given here. This is basically saying "redirect STDERR (2) to the same place as STDOUT (&1)". – rymo Jul 10 '15 at 21:26
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I usually get PID of running script by adding echo $! >> /tmp/pid.txt at the end of exec command but by redirecting output & error to /dev/null, no more pid file : does any of you can get PID of script launched by exec while not waiting for output ? – hugsbrugs Feb 22 '16 at 10:21
This answer provides a more comprehensive solution if you need to be able to check if the process is still running: https://stackoverflow.com/a/45966/814160 – Sean the Bean Jan 31 '18 at 21:49
Can't get any more perfect than this. Wish I saw this a few weeks ago. Thanks – user2993497 Oct 20 '19 at 01:21

score 28 · Answer 2 · answered Jun 19 '09 at 20:32

28

This will execute a command and disconnect from the running process. Of course, it can be any command you want. But for a test, you can create a php file with a sleep(20) command it.

exec("nohup /usr/bin/php -f sleep.php > /dev/null 2>&1 &");

answered Jun 19 '09 at 20:32

Brent Baisley

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is it better this or shell_exec ? – realtebo Nov 27 '15 at 10:38
hi, can i run function using this shell_exec("nohup /usr/bin/php -f http://example.com/notifications/sendnotifications_async > /dev/null 2>&1 &"); – Waseem Bashir Feb 01 '17 at 12:53
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Why *both* `nohup` and the `&`? – bugmenot123 Feb 28 '19 at 10:28

score 11 · Answer 3 · answered May 14 '13 at 15:03

11

You can also give your output back to the client instantly and continue processing your PHP code afterwards.

This is the method I am using for long-waiting Ajax calls which would not have any effect on client side:

ob_end_clean();
ignore_user_abort();
ob_start();
header("Connection: close");
echo json_encode($out);
header("Content-Length: " . ob_get_length());
ob_end_flush();
flush();
// execute your command here. client will not wait for response, it already has one above.

You can find the detailed explanation here: http://oytun.co/response-now-process-later

answered May 14 '13 at 15:03

Oytun

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Ops... I was waking a zombie question here, I havent realized. But this bit of information could be beneficial to others. – Oytun May 14 '13 at 15:04
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This has *nothing* to do with shell_exec – bugmenot123 Feb 28 '19 at 10:28

score 9 · Answer 4 · edited Oct 13 '11 at 12:46

On Windows 2003, to call another script without waiting, I used this:

$commandString = "start /b c:\\php\\php.EXE C:\\Inetpub\\wwwroot\\mysite.com\\phpforktest.php --passmsg=$testmsg"; 
pclose(popen($commandString, 'r'));

This only works AFTER giving changing permissions on cmd.exe - add Read and Execute for IUSR_YOURMACHINE (I also set write to Deny).

Pedro Lobito · Answer 5 · 2018-09-05T13:02:45.070

7

Sure, for windows you can use:

$WshShell = new COM("WScript.Shell");
$oExec = $WshShell->Run("C:/path/to/php-win.exe -f C:/path/to/script.php", 0, false);

Note:

If you get a COM error, add the extension to your php.ini and restart apache:

[COM_DOT_NET]
extension=php_com_dotnet.dll

edited Sep 05 '18 at 13:02

answered Feb 10 '17 at 09:20

Pedro Lobito

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I have no idea but it worked for me. Please anyone explain what wscript.shell is and what does it do. – GeekWithGlasses Aug 25 '17 at 23:39
can you please explain why this line is not giving any output? ` $oExec = $WshShell->Run('C:\Users\Shreyash\Desktop\phantomjs-2.1.1-windows\bin\phantomjs.exe -f C:\xampp\htdocs\composer\test_0.js', 0, false);` – GeekWithGlasses Aug 26 '17 at 00:08
You may have an error on test_0.js, check phantom log. – Pedro Lobito May 17 '19 at 11:23

score 6 · Answer 6 · edited Oct 13 '11 at 12:45

6

Use PHP's popen command, e.g.:

pclose(popen("start c:\wamp\bin\php.exe c:\wamp\www\script.php","r"));

This will create a child process and the script will excute in the background without waiting for output.

edited Oct 13 '11 at 12:45

Jason Plank

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answered Jun 26 '09 at 19:11

4

It waits for child process ends. At least on Win – Max Chernopolsky Feb 15 '16 at 05:17
The backgrounding here is achieved with the help of the Windows "start" command that prefixes the exe you want to run, it wont work if you omit it, and I wouldn't expect it to work on another OS... but it DOES works for me, thanks! :-) – Antony Dec 02 '16 at 15:42

score 1 · Answer 7 · answered Jun 19 '09 at 20:23

1

If it's off of a web page, I recommend generating a signal of some kind (dropping a file in a directory, perhaps) and having a cron job pick up the work that needs to be done. Otherwise, we're likely to get into the territory of using pcntl_fork() and exec() from inside an Apache process, and that's just bad mojo.

answered Jun 19 '09 at 20:23

chaos

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you said its a bad mojo. can you please elaborate? – Mayank Feb 07 '17 at 16:21

score 1 · Answer 8 · answered Jun 19 '09 at 23:58

That will work but you will have to be careful not to overload your server because it will create a new process every time you call this function which will run in background. If only one concurrent call at the same time then this workaround will do the job.

If not then I would advice to run a message queue like for instance beanstalkd/gearman/amazon sqs.

Is there a way to use shell_exec without waiting for the command to complete?

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