如何使用preg_replace（）删除除“Post”或“Posts”之外的任何内容？

I have a string that returns various stuff like numbers, spaces, etc. All I want from it is just "Post" or "Posts". Can someone give me an example of how to do this in PHP?

Yup, use preg_match like so:

$myData = "There are 15 posts in this forum.";
preg_match("/Posts?/", $myData, $results);
if($results[0][0] === "Posts") {
     // It was "posts"
} else {
     // Assume it was "post"
}

$post = preg_replace('/.*(Posts?).*/', '$1', $string);

If you just want to detect if the word Post is in the string, then using strpos() would be far more efficient.

if (strpos($string, 'Post') !== FALSE) {
   ... Post  is present ...
}

if you are testing to see if the string contains the word "Posts" then you could use something like this:

if (preg_match("/Posts/i", $theString)) {
  // do something
}

If I'm reading that correctly, it seems that you don't need the string Post/Posts, just if they exist. If that is the case the fastest way would be to use the strpos function. You could use it as follows:

if( strpos($haystack,"Post") !== false ) {
    //You get here if Post or Posts was found.
}