preg_replace in wordpress code example

Example 1: preg_replace

<?php
$string = 'April 15, 2003';
$pattern = '/(\w+) (\d+), (\d+)/i';
$replacement = '${1}1,$3';
echo preg_replace($pattern, $replacement, $string);

Example 2: preg_replace examples

$result = preg_replace(
    array('/pattern1/', '/pattern2/'),
    array('replace1', 'replace2'),
    $string
);