Check if a string is palindrome recursively

recpalcheck.php

<?php
 
// check if a string is a palindrome from the command line 
$inputstring = $argv[1];
 
function isPalindrome($inputstring)
{
    if (strlen($inputstring) <= 1){
        // if there is only one or zero characters, technically it's a palindrome
        return true;
    }
    else {

        if (substr($inputstring,0,1) == substr($inputstring,(strlen($inputstring) - 1),1)) {

             return isPalindrome(substr($inputstring,1,strlen($inputstring) -2));
            
            }
            else { 
            
                return false; 
            
            }
     }
}
 
if (isPalindrome($inputstring) == true){
 
    echo "\n\nCongrats you've got yourself a palindrome.\n\n";
 
}else {
 
    echo "\n\nSorry, This is not a palindrome\n\n";
}