how to redirect STDOUT to a file in PHP?

It is possible to write STDOUT directly to a file in PHP, which is much easier and more straightforward than using output bufferering.

Do this in the very beginning of your script:

fclose(STDIN);
fclose(STDOUT);
fclose(STDERR);
$STDIN = fopen('/dev/null', 'r');
$STDOUT = fopen('application.log', 'wb');
$STDERR = fopen('error.log', 'wb');

Why at the very beginning you may ask? No file descriptors should be opened yet, because when you close the standard input, output and error file descriptors, the first three new descriptors will become the NEW standard input, output and error file descriptors.

In my example here I redirected standard input to /dev/null and the output and error file descriptors to log files. This is common practice when making a daemon script in PHP.

To write to the application.log file, this would suffice:

echo "Hello world\n";

To write to the error.log, one would have to do:

fwrite($STDERR, "Something went wrong\n"); 

Please note that when you change the input, output and error descriptors, the build-in PHP constants STDIN, STDOUT and STDERR will be rendered unusable. PHP will not update these constants to the new descriptors and it is not allowed to redefine these constants (they are called constants for a reason after all).

here's a way to divert OUTPUT which appears to be the original problem

$ob_file = fopen('test.txt','w');

function ob_file_callback($buffer)
{
  global $ob_file;
  fwrite($ob_file,$buffer);
}

ob_start('ob_file_callback');

more info here:

http://my.opera.com/zomg/blog/2007/10/03/how-to-easily-redirect-php-output-to-a-file

No, output buffering is as good as it gets. Though it's slightly nicer to just do

ob_start();
echo 'xxx';
$contents = ob_get_flush();
file_put_contents($file,$contents);

None of the answers worked for my particular case where I needed a cross platform way of redirecting the output as soon as it was echo'd out so that I could follow the logs with tail -f log.txt or another log viewing app. I came up with the following solution:

$logFp = fopen('log.txt', 'w');

ob_start(function($buffer) use($logFp){
    fwrite($logFp, $buffer);
}, 1); //notice the use of chunk_size == 1

echo "first output\n";
sleep(10)
echo "second output\n";

ob_end_clean();

I haven't noticed any performance issues but if you do, you can change chunk_size to greater values.

Now just tail -f the log file:

tail -f log.txt