How can the Referer be used to determine the source of a page request in PHP?

The Referer header can be used in PHP to determine the source of a page request by checking the value of $_SERVER['HTTP_REFERER']. This can be useful for tracking where visitors are coming from or implementing referral-based functionality on a website. 

if(isset($_SERVER['HTTP_REFERER'])) {
    $referer = $_SERVER['HTTP_REFERER'];
    // Use $referer to determine the source of the page request
    echo "The page was accessed from: " . $referer;
} else {
    echo "No referer information available.";
}

Keywords

$_SERVER HTTP_REFERER parsing URL validation

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