Last updated: Fri, 05 Sep 2008

flush

(PHP 4, PHP 5)

flush — Flush the output buffer

Description

void flush ( void )

Flushes the output buffers of PHP and whatever backend PHP is using (CGI, a web server, etc). This effectively tries to push all the output so far to the user's browser.

flush() has no effect on the buffering scheme of your web server or the browser on the client side. Thus you need to call both ob_flush() and flush() to flush the output buffers.

Several servers, especially on Win32, will still buffer the output from your script until it terminates before transmitting the results to the browser.

Server modules for Apache like mod_gzip may do buffering of their own that will cause flush() to not result in data being sent immediately to the client.

Even the browser may buffer its input before displaying it. Netscape, for example, buffers text until it receives an end-of-line or the beginning of a tag, and it won't render tables until the </table> tag of the outermost table is seen.

Some versions of Microsoft Internet Explorer will only start to display the page after they have received 256 bytes of output, so you may need to send extra whitespace before flushing to get those browsers to display the page.

Return Values

No value is returned.

ob_clean

Output Control Functions

Last updated: Fri, 05 Sep 2008

add a note User Contributed Notes
flush

Sc@venger
02-Sep-2008 01:17


@Koalabear: in <pre> tags, try this:



function hardFlush() {

    // Koalabear solution with comments

    // Send 250 characters extra

    echo '<!--                                              ';

    echo '                                                  ';

    echo '                                                  ';

    echo '                                                  ';

    echo '                                               -->';

    flush();

    ob_flush();

}

Lucas
27-Aug-2008 11:12


I just had some problems with flush() and ob_flush(). What I did to resolve this problem took me some time to figure out so I'd like to share what I came up with.



The main problem is the php setting "output_buffering" which can be set too large and will prevent your text from outputting. To change this value you can either set it in php.ini or you can add the line 



php_value output_buffering "0"



to your .htaccess file. It will not work with ini_set() since it is PHP_INI_PERDIR.



Next thing is to begin with ob_start();

Then you need

ob_flush();

flush();

before any echo or print.



Your code might look like this:



<?php

ob_start();



for($i=0;$i<70;$i++)

{

    echo 'printing...<br />';

    ob_flush();

    flush();



    usleep(300000);

}



?>



Hope this helps anyone with the same problems.

David
07-May-2008 10:32


mod_security 2.x core rules will also prevent flush() from working.

3rowley at uppingham dot co dot uk
30-Apr-2008 07:08


It appears that the flush() command does not work when running under suPHP. I have had it explained to me that this is due to suPHP caching all the PHP output untill the connection has been terminated, thus making this command useless.



Hope that helps someone.

(Also, if anyone comes up with a cunning solution, I would love to hear)



Josh

marques at displague dot com
10-Apr-2008 06:23


flush() will prevent headers from being sent.



<?php

flush();

header('Location: testj.php');

?>



Warning: Cannot modify header information - headers already sent in testk.php on line 3

www.koalabear.nl
12-Mar-2008 12:19


This will work for IE 7.0 :)



Do not use within <PRE> tag because of the extra spaces send



function hardFlush() {

    // Like said in PHP description above, some version of IE (7.0 for example)

    // will not 'update' the page if less then 256 bytes are received

    // Send 250 characters extra

    echo '                                                  ';

    echo '                                                  ';

    echo '                                                  ';

    echo '                                                  ';

    echo '                                                  ';

    flush();

    ob_flush();

}

jr
25-Feb-2008 11:42


It's look like working for IE6 but not working for IE7.

dale3h
08-Nov-2007 05:41


When building a progress bar for a time intensive script, I came across a Firefox bug. I have only tested this in Firefox 2.0.0.9.



When using <div> tags for the progress bar, you MUST have a non-whitespace character inside the <div> upon initialization. If you do not, Firefox will freeze until the script is complete.

chuck at artistan dot org
27-Jun-2007 02:57


had problems flushing tables to screen.

this worked for me

<?

if (ob_get_level() == 0) ob_start();

loop{

    tables and stuff

    echo str_pad("<br>\n",8);

}

ob_flush();

flush();  // needed ob_flush

usleep(50000);// delay minimum of .05 seconds to allow ie to flush to screen

?>

mbilliet at gmail dot com
13-May-2007 11:13


Hello,



I had the same problems with sending a javascript after the <body></body> content has been sent to the browser (the script updates the content of an iframe).



Two solutions work for me:

   - add enough data (i.e.: extra dummy text like spaces) or,

   - echo the '</body>' tag at the end of the page



Note, that for the latter to work one should:

   - turn of output_buffering in php.ini and either:

      * turn on implicit_flush in its php.ini or,

      * call ob_implicit_flush(); at the beginning of a script



I preferr echoing the '</body>' tag at the end as it doesn't require any extra data to be sent over the wire and its much a neater coding technique.



Notes:

   - these worakarounds aren't needed when using perl and cgi,... .

   - you can leave the zlib.output_compression in your php.ini switched on



Kind regards and hoped this is of any help.



Maurits

macott[D0T]daiato[4T]gmail[D0T]com
24-Apr-2007 08:17


If flush() don't work remember to check if you have any antivirus caching the data sent to the browser.

Leon
30-Mar-2007 01:14


I've spent days trying to figure out why flush didn't work all of a sudden, while it used to work perfectly. Apparently, it was McAfee Spamkiller that caused problems. Disabling it didn't work, I had to completely remove it. Hope this helps someone.

Kirk
06-Feb-2007 08:25


If you're not explictly using the buffering functions, then ob_flush() is only necessary if output buffering is turned on in your php.ini file.



flush() is only necessary if implicit_flush is turned off in your php.ini file. Setting implicit_flush to on will remove the need for all these flush() calls, but it's generally only good in an extremely controlled environment. Turning on implicit_flush in a production environment can be bad.

anonymous
10-Nov-2006 10:42


Also, if you don't have a global php.ini file, PHP will laugh at you for calling flush()... and so will I.

no at spam dot com
03-Aug-2006 07:51


ob_flush();flush();



Not the other way around, because it wont work.

vlad at modomail dot com
05-Apr-2006 02:46


Sorry if this is off topic, but it's the closest place I could find :)  I had an issue with essentially running a CPU intensive task while updating the browser with a progress bar via javascript and flushing the buffer a lot.



When the script was running, it effectively blocked other pages from running.  I had a few extra httpd_preforks processes just waiting to be used, but they just sat there.  I wasn't reading a file, locking database tables or anything that I would suspect an exclusive lock on, just outputting a bunch of text to the browser.  I even tried throttling my loops to see if it was processor related but still had problems.



Finally, I found this in the php.ini file and changed the On to Off and it worked.



[Sockets]

; Use the system read() function instead of the php_read() wrapper.

sockets.use_system_read = Off



Posting in case someone else has the same issue (or if someone knows why this would make a difference :) ).

mega023 at gmail dot com
25-Nov-2005 11:54


If flush is not working probably mod_gzip is enabled.

To disable it just add following lines to .htaccess



<IfModule mod_gzip.c>

mod_gzip_on no

</IfModule>

PuTTYshell
20-Nov-2005 03:06


<?php

  header('Content-type: multipart/x-mixed-replace;boundary=endofsection');

  print "\n--endofsection\n";



  $pmt = array("-", "\\", "|", "/" );

  for( $i = 0; $i <10; $i ++ ){

      sleep(1);

      print "Content-type: text/plain\n\n";

      print "Part $i\t".$pmt[$i % 4];

      print "--endofsection\n";

      ob_flush();

      flush();

  }

  print "Content-type: text/plain\n\n";

  print "The end\n";

  print "--endofsection--\n";

?>

Server Push with "multipart/x-mixed-replace", tested on Firefox 1.07.

This is an example requiring both ob_flush and flush.

mikael at oebb dot net
03-Oct-2005 09:47


Hi all.

Been scratching my head over data NOT flushed to IE (6) even though I tried strpad 4096 chars, all headers OK,  TABLE and no TABLE, flush and ob_flush - still a blank page. Tried adding a sleep(1) before flushing - and everything worked as a charm.  



/Mikael

20-Sep-2005 08:37


In my testing, Internet Explorer 6.0 wouldn't flush anything nested in <table> or <td> tags, regardless of padding. But at the <body> level everything flushed with no fuss -- no padding or tags required.



Both Firefox 1.0 and Safari 2.0 could flush within tables, and both required a tag after the text (like <br>). Safari could flush only after the first 1024 characters where received. Firefox needed at least 8 characters per flush (but it could flush anything at the <body> level).



So the only thing that worked on all those browsers was this:



<html>

<body>

<?php  // not in table tags for IE

echo str_pad('',1024);  // minimum start for Safari

for ($i=10; $i>0; $i--) {

    echo str_pad("$i<br>\n",8);

    // tag after text for Safari & Firefox

    // 8 char minimum for Firefox

    flush();  // worked without ob_flush() for me

    sleep(1);

}

?>

</body>

</html>

StanV
08-Aug-2005 09:15


So will this:



<?php



for ($i = 0; $i<10; $i++){



       echo "<br> Line to show.";

       echo str_pad('',4096)."\n";    



       flush();

       sleep(2);

}



echo "Done.";



?> 



I've not found a case where I need to use ob_flush() if I never started caching the buffer in the first place.



There seems to be some confusion you have to start buffering the output to make sure you flush it later with both commands. 



If you don't need to buffer with ob_*, only flush() is enough in my experience.

js at jeansebastien dot com
17-Jul-2005 07:41


This will show each line at a time with a pause of 2 seconds.

(Tested under IEx and Firefox)



<?php



if (ob_get_level() == 0) ob_start();



for ($i = 0; $i<10; $i++){



        echo "<br> Line to show.";

        echo str_pad('',4096)."\n";    



        ob_flush();

        flush();

        sleep(2);

}



echo "Done.";



ob_end_flush();



?>

Colin at ColinsRealm dot Com
13-Jul-2005 02:54


I find that you need to open your ob for it to print . Heres my example that works in IE . Yes - the strings need to be long for it to flush ...



ob_start();

for($i = 1; $i <= 10; $i++){

    $sourceName = 'filetoupload' . $i;

    $imageArray = array();

    if(!is_uploaded_file($_FILES[$sourceName]['tmp_name'])) { $imageArray[$num-1] = NULL; $message="Image $i does not exist (has not been prompted for upload)<br/>"; }

    else {

        move_uploaded_file($_FILES[$sourceName]['tmp_name'], "temporary/$sourceName");

        $message = "Image $i has been uploaded to the server";

    }

    echo $message;

    flush();

    ob_flush();

    usleep(300);

}

ob_end_flush();

Vladimir Kornea of typetango.com
02-Jun-2005 03:37


The documentation for flush() states:



flush() has no effect on the buffering scheme of your webserver or the browser on the client side. Thus you need to call both ob_flush() and flush() to flush the output buffers.



What it does not state is the order in which the functions should be called. This is the correct order:



ob_flush();

flush();



These functions do not need to be called repeatedly (as other have stated), merely in the correct order.

MOELZE �T GMX DOt DE (Michael)
16-May-2005 12:38


It is a bit complicated to work with the funktion flush() and you have to experiment with it a bit.

So if you design a site which has a timeloop at the end that calls a other site via a form data input (Data Submit) you have

to give something out to the buffer to get that new site loaden quick.



For example:



$instant=gettimeofday();

$timenow=$instant["sec"];//Start Time



//timeloop(e.g. for security_save after 30 min)

while (1) { echo "<b></b>";//Useless (only to quickload next

                                    //or same Site when do a switch)

flush();                          //giveout buffer

$instant=gettimeofday();

$timeactual=$instant["sec"]; //get Actual Time in Secs

$flag=(($timeactual>$timenow+$diff)? 1:0);//$diff=switchTime

if ($flag) { what_do_at_switch_Time();//Sec.Save etc.etc.

$timenow=$timeactual; } //Set new Start Time

sleep(5); //Or so...(Important)

} //End of while-Loop



So you can programm a security save or other function in your site and if you do a switch the upload of the new or same site (the called site) works...

Alex
22-Apr-2005 10:35


Modified progress bar.. Works in IE, Mozilla+FF.



<html>

<head>

<style type="text/css"><!--



div {

 margin: 1px;

 height: 20px;

 padding: 1px;

 border: 1px solid #000;

 width: 275px;

 background: #fff;

 color: #000;

 float: left;

 clear: right;

 top: 38px;

 z-index: 9

}



.percents {

 background: #FFF;

 border: 1px solid #CCC;

 margin: 1px;

 height: 20px;

 position:absolute;

 width:275px;

 z-index:10;

 left: 10px;

 top: 38px;

 text-align: center;

}



.blocks {

 background: #EEE;

 border: 1px solid #CCC;

 margin: 1px;

 height: 20px;

 width: 10px;

 position: absolute;

 z-index:11;

 left: 12px;

 top: 38px;

 filter: alpha(opacity=50);

 -moz-opacity: 0.5;

 opacity: 0.5;

 -khtml-opacity: .5

}



-->

</style>

</head>

<body>



<?php



if (ob_get_level() == 0) {

    ob_start();

}

echo str_pad('Loading... ',4096)."<br />\n";

for ($i = 0; $i < 25; $i++) {

    $d = $d + 11;

    $m=$d+10;

    //This div will show loading percents

    echo '<div class="percents">' . $i*4 . '%&nbsp;complete</div>';

    //This div will show progress bar

    echo '<div class="blocks" style="left: '.$d.'px">&nbsp;</div>';

    flush();

    ob_flush();

    sleep(1);

}

ob_end_flush();

?>

<div class="percents" style="z-index:12">Done.</div>

</body>

</html>

storm at stormfx dot com
16-Apr-2005 04:25


Remember when trying to output partial content, that PHP's .ini file setting affects whether or not it succeeds, depending on how you code it, of course. Here's an example using a progress bar done soley in PHP:



// Some HTML/CSS to spice up the spaces...

<html>

<head>

<style type="text/css"><!--

.pbar {

    background: #EEE;

    border: 1px solid #CCC;

    margin: 1px;

    height: 10px;

    width: 10px;

}--></style>

</head>

<body>



<?php

// If the buffer is not set to 0, there's no need to call

// ob_start(), because the buffer is started already.

// You can test that by a call to ob_get_level();. Calling it

// again will cause a second level of buffering to start and

// the script won't work.



if (ob_get_level() == 0) {

    ob_start();

}

echo str_pad('Loading... ',4096)."<br />\n";

for ($i = 0; $i < 25; $i++) {

    echo '<span class="pbar">&nbsp;</span>';

    ob_flush();

    usleep(700000);

}

ob_end_flush();



// Close it out...

?>

</body>

</html>



Note: This is just an example. Normally it's bad practice to use the OB like this :)



This was tested with PHP 5.04 on WinXP Pro/IIS 5.1

Marty
15-Apr-2005 04:33


This is an extention of Rusty's comment below: 



After sitting here for hours trying to make IE6 flush data out in the middle of a page (with it working perfectly in Firefox), I finally figured out the problem. IE will not display flushed data (even if it has it) unless the table that contains it is complete.



Every new element you want IE to display must not be in ANY kind of table at all. You must end all your tables.

Ghostshaw at spymac dot com
07-Apr-2005 12:45


I would like to point out that there is a function to replace ob_flush and flush. If you set ob_implicit_flush(true); at the top of the page it will automatically flush any echo or print you do in the rest of the script.



Note that you still need a minimum amount of data to come through the browser filter. I would advice using str_pad($text,4096); since this automatically lenghtens the text with spaces to 4 KB which is the minimum limit when using FireFox and linux.



I hope this helps you all out a bit.

matt at nospamplease dot hevanet dot com
21-Mar-2005 06:42


Like IE, Safari needs a fair amount of data before it'll display anything, actually more than explorer.  The following code works for me in Firefox and Safari, and should work in IE as well.



<?php



for($i = 0; $i < 40000; $i++)

{

echo ' '; // extra spaces

}

// keeps it flowing to the browser�

flush();

// 50000 microseconds keeps things flowing in safari, IE, firefox, etc

usleep(50000);



?>



This code came from a comment on a blog discussing browser functionality with flush();

crmacd at yahoo dot com
04-Mar-2005 11:28


I figured out a way to create a simple progress bar that is for the most part cross platform. Seeing as I got my ideas from this site it's only share to give back to the community.



Note: Something interesting about browser buffering... you have to have the <html><body> for Firefox and some other browsers to recognize items by their id in Javascript. So I recommend using some sort of header function before calling this function.



<?php



function fn_progress_bar($intCurrentCount = 100, $intTotalCount = 100)

{

    static $intNumberRuns = 0;

    static $intDisplayedCurrentPercent = 0;

    $strProgressBar = '';

    $dblPercentIncrease = (100 / $intTotalCount);

    $intCurrentPercent = intval($intCurrentCount * $dblPercentIncrease);

    $intNumberRuns++;

        

    if(1 == $intNumberRuns)

    {

        $strProgressBar = <<< BAR

<table width='50%' id='progress_bar' summary='progress_bar' align='center'><tbody><tr>

<td id='progress_bar_complete' width='0%' align='center' style='background:#CCFFCC;'>&nbsp;</td>

<td style='background:#FFCCCC;'>&nbsp;</td>

</tr></tbody></table>

<script type='text/javascript' language='javascript'>

function dhd_fn_progress_bar_update(intCurrentPercent)

{

    document.getElementById('progress_bar_complete').style.width = intCurrentPercent+'%';

    document.getElementById('progress_bar_complete').innerHTML = intCurrentPercent+'%';

}

</script>

BAR;

    }

    else if($intDisplayedCurrentPercent <> $intCurrentPercent)

    {

        $intDisplayedCurrentPercent = $intCurrentPercent;

        $strProgressBar = <<< BAR

<script type='text/javascript' language='javascript'>

dhd_fn_progress_bar_update($intCurrentPercent);

</script>

BAR;

    }

    if(100 <= $intCurrentPercent)

    {

        $intNumberRuns = $intDisplayedCurrentPercent = 0;

        $strProgressBar = <<< BAR

<script type='text/javascript' language='javascript'>

document.getElementById('progress_bar').style.visibility='hidden';

</script>

BAR;

    }

    echo $strProgressBar;

    flush();

    ob_flush();

}



?>

siggi AT june systems DOT com
04-Mar-2005 03:54


After searching through the PHP site, google and various forums, not finding a solution to my script not outputting anything while calling flush and ob_flush, I thought of trying to tell PHP to call:



session_write_close();



before starting echo'ing. It worked like a charm. I couldn't find any references to this, so I hope this note will help someone in the future.

Squ1sher
01-Feb-2005 08:25


On Windows xampp 1.3 with php 4.3.4 is use this functions


to force a flush.


<?php


function dummyErrorHandler ($errno, $errstr, $errfile, $errline) {


}





function forceFlush() {    


    ob_start();


    ob_end_clean();


    flush();


    set_error_handler("dummyErrorHandler");


    ob_end_flush();


    restore_error_handler();


}


?>





ob_end_flush generates a warning, which is supressed, using the dummy-errorhander. You could also use @, but then nusphere will also print the warning.

mat.wilmots (at) wanadoo (dot) fr
11-Nov-2004 12:26


This code does not work as expected



<pre>

<?php



echo "Test1\n";

flush();

sleep(3);



echo "Test2\n";



?>

</pre>



It should print Test1, wait 3 seconds then print Test2 but actually it prints everything at the end.

It seems PHP is doing output buffering on its own, here is the way to make it work :



<pre>

<?php



ob_end_flush();



echo "Test1\n";

flush();

sleep(3);



echo "Test2\n";



?>

</pre>



You don't really need to repeat some "fake" text to fill the buffer in order to make this effect.

matt (at) roughest (dot) net
06-Oct-2004 12:57


Something about the Linux version of Firefox makes flush() not work. Not sure if this is specifically a Firefox problem, or something about the way Linux handles HTTP streams, but nothing gets rendered until the HTTP stream is closed.



Interestingly, flush() works fine running IE on Linux under Wine.

Rusty
24-Feb-2004 05:25


Netscape will flush the output as expected at the point it is called from within your script. IE, however, needs a boost.



IE seems to have a condition where it will flush data when it hits an end (</table>) tag AND has at least 256 chars of data.



So, pad your output with necessary spaces, wrap your progressing data around open (<table>) and end (</table>) tags, and then call flush() so that one script will work for Netscape as well.



TESTING ENVIRONMENT

IE: Ver/6.0.2800

Netscape: Ver/7.1

PHP: Ver/4.3.4

Apache: Ver/1.3.27

phpnote at mijav dot dk
23-Jan-2004 11:46


If you are having trouble makeing flush(); or ob_flush(); work the way you want, try both of them.



Using PHP 4.3.3RC1 there was no effect using flush() or ob_flush(), however a combination of both gave me perfect results.



Example:



<?

echo str_repeat(" ", 256);

$i = 100;

while($i > 0)

{

   echo $i." bottle".($i != 1 ? 's' : '')." of beer on the wall, ".$i." bottle".($i != 1 ? 's' : '')." of beer. Take one down and pass it around, ".(--$i)." bottle".($i != 1 ? 's' : '')." of beer on the wall<br>\n";

   flush();

   ob_flush();

   usleep(50000);

}

?>



This could be the result of a server-issue - maybe you are using a public server that has OB enabled by default.

viazenetti
20-Jan-2004 08:25


Note to my last posting:

Since version 4.2.0 you can use ob_flush() instead. This works fine with sessions and cookies disabled.

m@rco
29-Oct-2003 03:22


in order to display in HTML pages something like a "progress bar" or if you want to force the web server to flush output to the browser, or the browser to flush as well, you can print a long enough "dummy" string to make the output buffer grow, as you probably know, like:



print "[";



for($i = 0; $i < 100; $i++){

  $spaces.=" ";

} // for



//and then



for($i = 0; $i < 10; $i++){

  for($ii = 0; $ii < 200000; $ii++){

    //do something slow here

  } // for

  print "$spaces|";

  flush();

} // for



print "]";



/*

but this somethin may be not really what you expect in

a progress bar, as it prints spaces (although rendered as single by the browser) between the bar units..

you can solve this using 

  $spaces.="<!-- bufferme -->";



/*



print "[";



for($i = 0; $i < 100; $i++){

  $spaces.="<!-- bufferme -->";

} // for



//and then



for($i = 0; $i < 10; $i++){

  for($ii = 0; $ii < 200000; $ii++){

    //do something slow here

  } // for

  print "$spaces|";

  flush();

} // for



print "]";



//which looks nice as a progress bar..

scottmacvicar at ntlworld dot com
01-Oct-2003 03:40


Regarding Apache2

flush() will produce the same results as ob_flush() when output buffering is involved.

jthome at fcgov dot com
23-Jul-2003 09:52


This may not be obvious from the previous posts.  



You must flush all HTML up to and including the <body> tag (<head>, <meta>, etc.), or the browser won't respond.  This would have the effect of "blanking" the page while waiting for the script to complete.  This is in addition to the other tips posted.



Most users expect something immediate to happen when they click on a link.  "Blanking" the page is often times better for those not accustomed to keeping an eye on their browser's progress bar.

add a note

ob_clean

Output Control Functions

Last updated: Fri, 05 Sep 2008