Execute a PHP file only if it has changed

<?php
/**
 * Execute a PHP file given by the -f option only if it has changed
 * @author [email protected]
 * @link http://www.fijiwebdesign.com/
 */
 
// eg: php watch.php -f test.php 
//     will have $file = test.php
$opts = getopt("f:");
$file = $opts['f'];
 
if (!is_file($file)) {
  die('Please specify a file via the -f option.');
}
 
// should we execute file
$exec = false;
 
// our compare for this file changes 
$meta_file = sys_get_temp_dir() . '/' . md5($file);
// our file where output is saved
$output_file = $meta_file . '-out';
 
// current hash of file contents
$curr_hash = md5(file_get_contents($file));
 
// old hash of file contents
if (file_exists($meta_file)) {
  $old_hash = file_get_contents($meta_file);
 
  // if the hashes do not match, a change occurred in content
  if ($old_hash != $curr_hash) {
    // execute file since it changed
    $exec = true;
  } 
 
} else {
  // execute file since first run
  $exec = true;
}
 
// save the current file content hash to our meta file
file_put_contents($meta_file, $curr_hash);
 
// our ouput buffer
$output = '';
 
// execute our file if changed
if ($exec) {
  ob_start();
  require($file);
  $output = ob_get_clean();
 
  // save output for display later also
  file_put_contents($output_file, $output);
} else {
  if (file_exists($output_file)) {
    $output = file_get_contents($output_file);
  }
}
 
// display our output
echo $output;