Question

Just as a demo, try the following code:

<?php
echo '<pre>';      
ob_end_flush();
for($i=0;$i<2;$i++) {
passthru("ping -n 8 127.0.0.1");
@ob_flush();
}
echo '</pre>';
?>

This is the output:

Pinging stackoverflow.com [64.34.119.12] with 32 bytes of data:
Reply from 64.34.119.12: bytes=32 time=28ms TTL=56
Reply from 64.34.119.12: bytes=32 time=29ms TTL=56
Reply from 64.34.119.12: bytes=32 time=29ms TTL=56
Reply from 64.34.119.12: bytes=32 time=28ms TTL=56

Ping statistics for 64.34.119.12:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 28ms, Maximum = 29ms, Average = 28ms

Pinging stackoverflow.com [64.34.119.12] with 32 bytes of data:
Reply from 64.34.119.12: bytes=32 time=28ms TTL=56
Reply from 64.34.119.12: bytes=32 time=27ms TTL=56
Reply from 64.34.119.12: bytes=32 time=26ms TTL=56
Reply from 64.34.119.12: bytes=32 time=29ms TTL=56

Ping statistics for 64.34.119.12:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 26ms, Maximum = 29ms, Average = 27ms

It actually does it twice (which is from the “is less than 2” loop). If you test the script, you’ll notice that it takes a few seconds to do the first one, then it outputs it all at once. After that (second loop) it goes line by line. My goal is just to have a single output, go line by line and not buffer any output, like the following does except as it happens:

<?php
system("ping -n 8 127.0.0.1");
?>

Note: This is running on a Windows server with PHP 5.

Answer 1

So, what is happening here is your browser is likely buffering. I think if you look at a packet sniffer, your flushes are probably working.

Just to be sure, call flush() as well as ob_flush().

You can never clear out all of the buffers, as PHP is only aware of its own. The server can buffer, and the clients almost always buffer.