使用“{}”和“？”的Preg_match（）用法

Question

I'm currently trying things with reggae (PCRE) and PhP.

It seems that the function pre_match() does not work properly with the signs {} and ? and I'm wondering why. Can someone help me?

Here is the code I'm using just for the example:

    <?php
        $search = "aaaah";

        //Return "valid" while I ask for 3 "a" specifically
        if(preg_match("&a{3}&", $search)){
              echo 'Valid <br/>';
        }else{
              echo 'Invalid <br/>';
        }

        //Also return "valid" while I ask for 0 or 1 "a"
        if(preg_match("&a?&", $search)){
              echo 'Valid <br/>';
        }else{
              echo 'Invalid <br/>';
        }
    ?>

There must be something I misunderstood. Can someone explain? I did not find anything anywhere. Thank you in advance!

I'm using MAMP with a Mac and coding in utf-8.

Answer 1

The results you get are expected as:

1. You ask for 3 a 's in a row and in your example there are two of those series possible, the first 3 a 's and the last 3 a 's. So that is a match as you don't specify what has to happen before or after your series of 3 a 's.
2. You ask for an optional a character. Any input will match that as you are looking for 0 or 1 a's and that will always be true for everything you feed it, whether it contains a 's or not.