如果文件夹和单页的正则表达式我如何使用PHP

<?php if (preg_match('/\/(contact|news)\//', $_SERVER['REQUEST_URI']) === 1): ?>
   <a href="/">link</a>
<?php endif; ?>

Is there a way I can also specify a single page such as /index.html in a regex specifying folders in a php if?

Try the below :

<?php if (preg_match('/\/(contact|news)\/index\.html/', $_SERVER['REQUEST_URI']) === 1): ?>
   <a href="/">link</a>
<?php endif; ?>

UPDATE

Based on your comment below this is the code that should work :

<?php
// you can add .* after index\.html you want to match index.html with get variables
echo preg_match('/\/(index\.html.*|contact\/.*|news\/.*)/','/index.html');
// or just make it strict to match only index.html
echo preg_match('/\/(index\.html|contact\/.*|news\/.*)/','/index.html');
echo '<br>';
echo preg_match('/\/(index\.html|contact\/.*|news\/.*)/','/contact/blablabla');
echo '<br>';
echo preg_match('/\/(index\.html|contact\/.*|news\/.*)/','/news/blablabla');

?>

Written like this:

<?php 
if (preg_match('/\/(contact\/|news\/|index\.html)/', $_SERVER['REQUEST_URI'])): 
?>

You can define as many pages as you like (note the last / has been moved). Though, that could very quickly become unwieldy.

You may also wish to consider using preg_quote:

<?php 
$startsWith = array(
    'contact/',
    'news/',
    'index.html'
);
foreach($startsWith as &$string) {
    $string = preg_quote($string);
}
if (preg_match('/\/(' . implode('|', $startsWith) . ')/', $_SERVER['REQUEST_URI'])): ?>

Which, especially if unfamiliar with regex syntax, would make managing things a little easier.