PHP is an interpreter much like Bash, Python, etc, so you can do "normal" scripting with it. For example:
#!/usr/bin/php5
<?php
echo "Hello, world!\n";
while($line = fgets(STDIN)) {
echo "> " . $line;
}
?>
Mark the file as executable, then run:
$ /program/that/generates/lines | /path/to/your/php/script
However, contrary to your original question, it sounds to me like you actually want to use JavaScript and possibly AJAX for web purposes. Sane web applications will have the said script run in the background and safely write the results to a file or stream, using AJAX to read it and update the information on the current page.