How to execute shell cmd (python) using php and print all constant-updated outputs? -

i pretty new php actually. here's thing: want make simple web-shell well-known youtube-dl, made simple webpage , simple php page, trying use php execute youtube-dl , display outputs browser.

i've try command thing , escapeshellcmd(), both of them can output first few lines of constant-updating outputs youtube-dl (and work other cmd "ls"), seems when first line, python script stop, no more updates, , there no downloaded video file on server.

btw, it's on ubuntu 14 lts.

so far, have tried these:

    <?php     $command = shell_exec('youtube-dl https://www.youtube.com/watch?v=z456k6ybeo0');     echo "<pre>$command</pre>";     ?> 

and

    <?php     echo `youtube-dl https://www.youtube.com/watch?v=z456k6ybeo0`     > 

and

    <?php     $command = escapeshellcmd('youtube-dl https://www.youtube.co/watch?v=z456k6ybeo0');     $output = shell_exec($command);     echo $output;     ?> 

both of them work "ls",but not working youtube-dl

try shell_exec function:

<?php $output = shell_exec('ls -lart'); echo "<pre>$output</pre>"; ?>