Simple function to get file extension

The method is a bit clumsy, but the idea is relatively clear, and it is written for novices, so the explanation is a bit long-winded, so experts should avoid it :)
Reprinted from PHP interview questions: http://phpmst.com/

$path=str_replace('\','/',__FILE__);//Slightly adjust the format of the file path and replace \ with /
function substr_1($path){
 $ str_1= strrchr($path,'.');//Get the content after . and . in the file path
 $str_2=(strpos($str_1,'?')===false)?$str_1:preg_replace(' /[?][w]*/','',$str_1);
/*
Determine whether the file contains parameters. If you just get the file on the computer, there will definitely be no parameters. You can ignore this step. , but if it is a url, it may have parameters such as ?a=444&b=33. We only need to get the extension name, so we need to remove these parameters. Here we use regular expressions to replace them all with empty characters. ;
*/
 return ltrim($str_2,'.');//If you want to get the ".php" format, you can remove this step. If you want to get the "php" format, keep this step;
}
//The following is the test
echo substr_1($path);
?>