foo.plx

#!/usr/bin/perl
# foo.plx
# This is what the other file sends its contents to.

open(FILE, ">/tmp/foo");

print FILE "----start----\n";

# Write all of the piped input to the FILE
while(<STDIN>) {
  print FILE $_;
}

print FILE "----end----";

close(FILE);

web.php

<?php
// Create the process, naming the in/out pipes.
$proc = proc_open(
  '/home/sbisbee/src/foo.plx',
  array( array('pipe', 'r'), array('pipe', 'w') ),
  $pipes
);

if(is_resource($proc)) {
  // Get this file's contents ($_SERVER['SCRIPT_FILENAME']) and write them
  fwrite($pipes[0], file_get_contents($_SERVER['SCRIPT_FILENAME']));
  fclose($pipes[0]);

  // See what the script returns to us (if anything)
  echo '<div>' . stream_get_contents($pipes[1]) . '</div>';

  // Always make sure you clean up your procs before terminating.
  fclose($pipes[1]);
  echo 'command returned ' . proc_close($proc);
}
else {
  echo 'could not open the process';
}
?>