PHP obtiene flujo de salida o simplemente eco

The first thing that comes to mind for me is output buffering. echo y print interface with the output buffering mechanism, but directly writing to stdout bypasses it.

Considere este guión:

<?php
$stdout = fopen('php://stdout', 'w');
ob_start();
        echo "echo output\n";
        fwrite($stdout, "FWRITTEN\n");
        echo "Also echo\n";
$out = ob_get_clean();
echo $out;

que salidas:

FWRITTEN
echo output
Also echo

which demonstrates that echo is buffered, and fwrite is not.

La diferencia es que echo escribe a php://output which is the output buffer stream. However, php://stdout gives you direct access to the processes' output stream which is unbuffered.

Further information regarding streams can be found in the manual: http://www.php.net/manual/en/wrappers.php.php

In addition to the already noted technical difference, there's also the obvious difference in style and convention. echo/print is the normal way of producing output in PHP; writing to output as if to a file would be abnormal and potentially confusing. For the sake of the clarity of your intent, I wouldn't advise doing this unless you have a good reason to do so.

Aquí php://stdout is not buffered stream, fwrite can buffer the output using php://output