<?php
$arraystring = ['cat','google','test','catty', 'meow'];
$substring = 'at';
filter($arraystring,$substring);
function filter ($arraystring,$substring){
    $resultarray = array();
    foreach ($arraystring as  $substringword) {
        $checkSubstring = sub($substringword,$substring);
        if ($checkSubstring){
            $resultarray[] = $substringword;
        }
    }

    return $resultarray;
}

function sub($substringword,$substring){
    for ($i = 0; $i <strlen($substringword); $i++) {
                    $checkResult = 0;
        for ($j = 0;$j < strlen($substring);$j++){
            if ($substringword[$i + $j] === $substring[$j])  {
                $checkResult++;
                if ($checkResult == strlen($substring)) {

                    return true;
                }

            }
        }
    }
        return false;
}
var_dump(filter($arraystring,$substring));