preg_replace在数组php中

$search = array("<?php", "god", "gOd"); //do not want to do this in so many words\\
$replace = array("<-php", "God", "God");
$comment = str_replace($search, $replace, mysqli_real_escape_string($conexao, $_POST['comment']));

I want to include uppercase and lowercase letters in the array, how to do this for $search and $replace?

If you have to use regular expressions, write your code like this:

preg_replace('/regular expression here/i', 'replacement here', $string);

Otherwise use str_ireplace(): http://php.net/manual/en/function.str-ireplace.php

<?php
$db = new mysqli('localhost', 'root');
$a = array("<?php", "god", "gOd");
foreach ($a as &$v) {
    $v = mysqli_real_escape_string(
        $db,
        preg_replace("/[^A-Za-z0-9?!]/", '', $v)
    );
}
var_export($a);

Result:

array (
  0 => '?php',
  1 => 'god',
  2 => 'gOd',
)