PHP Judgment URL originated

PHP Judgment URL Source
Q: Besides using $_server[' http_referer ' to judge

There's no other way. Determine the source of the previous URL.
------to solve the idea----------------------
Http_referer is an incoming CGI environment variable and does not always exist
The browser address bar does not have access, the client can also control does not emit

Use $_server[' Http_referer '] to determine if he has
if (Isset ($_server[' http_referer ')) {
echo $_server[' Http_referer '];
}
------to solve the idea----------------------
PHP only http_referer to judge.
But if the direct access to the page, there is no http_referer, so need to judge
if (Isset ($_server[' http_referer ')) {
echo $_server[' Http_referer '];
}

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