flush output error

hi guys i have a little problem with flushing the buffer output, in this loop it should be downloading a file and changing the progress of a progress bar, although it waits until the shell_exec of all the files are done and then flushes the buffer which will start @ 95% , so it wont start until shell_exec is finished , is this a bug ? foreach ($filename as $file){ shell_exec("curl -O ".$url.$file); //shell_exec("wget ".$url.$file); //echo $file; $bar->progressbar_percentage($i,$filename,'NewWin','Percentage','Downloading '.$file); $i++; }