Caesar Cipher Encryption in PHP

file.php

<?php

// test case in https://www.hackerrank.com/challenges/linkedin-practice-caesar-cipher/problem

$input = 'DNFjxo?b5h*5<LWbgs6?V5{3M].1hG)pv1VWq4(!][DZ3G)riSJ.CmUj9]7Gzl?VyeJ2dIPEW4GYW*scT8(vhu9wCr]q!7eyaoy.';

$step = 45;

foreach (range('a', 'z') as $value)
{
    $az_lower[$i] = $value;
    $az_upper[$i] = strtoupper($value);
}

$input_array = str_split($input);

foreach ($input_array as $character) 
{
    if (preg_match("/^[a-zA-Z]+$/", $character))
    {
        if (ctype_lower($character))
        {
            $position = array_search($character, $az_lower) + $step;
            if ($position > 26)
            {
                $position = ($position % 26);
                if ($position === 0) 
                {
                    $position = 26;
                }
            }
            echo $az_lower[$position];
        } else 
        {
            $position = array_search($character, $az_upper) + $step;
            if ($position > 26)
            {
                $position = ($position % 26);
                if ($position === 0) 
                {
                    $position = 26;
                }
            }
            echo $az_upper[$position];
        }
    } else
    {
        echo $character;
    }
}