$word2compare = "stupid";
$words = array(
  'stupid',
  'stu and pid',
  'hello',
  'foobar',
  'stpid',
  'upid',
  'stuuupid',
  'sstuuupiiid',
);
while(list($id, $str) = each($words)){
  similar_text($str, $word2compare, $percent);
  print "Comparing '$word2compare' with '$str': ";
  print round($percent) . "%\n";
}
/*
Results:
Comparing 'stupid' with 'stupid': 100%
Comparing 'stupid' with 'stu and pid': 71%
Comparing 'stupid' with 'hello': 0%
Comparing 'stupid' with 'foobar': 0%
Comparing 'stupid' with 'stpid': 91%
Comparing 'stupid' with 'upid': 80%
Comparing 'stupid' with 'stuuupid': 86%
Comparing 'stupid' with 'sstuuupiiid': 71%
*/