HTTP Request Headers in PHP

In PHP, you can get the values of request headers. They are contained in the $_SERVER superglobal array. The key for each request header starts with 'HTTP_', followed by the name of that header in uppercase letters.

Let's, for example, get the contents of the Host header:

php<?php
  echo $_SERVER['HTTP_HOST'];
?>

If the header name contains hyphens, they are converted to underscores in the key in PHP. As an example, let's get the contents of the header Accept-Encoding:

php<?php
  echo $_SERVER['HTTP_ACCEPT_ENCODING'];
?>