Can I read the hash portion of the URL on my server-side application (PHP, Ruby, Python, etc.)?

The main problem is that the browser won't even send a request with a fragment part. The fragment part is resolved right there in the browser. So it's reachable through JavaScript.

Anyway, you could parse a URL into bits, including the fragment part, using parse_url(), but it's obviously not your case.

Simple test, accessing http://localhost:8000/hello?foo=bar#this-is-not-sent-to-server

python -c "import SimpleHTTPServer;SimpleHTTPServer.test()"
Serving HTTP on 0.0.0.0 port 8000 ...
localhost - - [02/Jun/2009 12:48:47] code 404, message File not found
localhost - - [02/Jun/2009 12:48:47] "GET /hello?foo=bar HTTP/1.1" 404 -

The server receives the request without the #appendage - anything after the hash tag is simply an anchor lookup on the client.

You can find the anchor name used within the URL via javascript using, as an example:

<script>alert(window.location.hash);</script>

The parse_url() function in PHP can work if you already have the needed URL string including the fragment (http://codepad.org/BDqjtXix):

<?
echo parse_url("http://foo?bar#fizzbuzz",PHP_URL_FRAGMENT);
?>

Output: fizzbuzz

But I don't think PHP receives the fragment information because it's client-only.

It is retrievable from Javascript - as window.location.hash. From there you could send it to the server with Ajax for example, or encode it and put it into URLs which can then be passed through to the server-side.

The hash is never sent to the server, so no.

What about:

Dynamically grab the #hash

<script>
var urlhash = window.location.hash, //get the hash from url
    txthash = urlhash.replace("#", ""); //remove the #
    //alert(txthash);
</script>

<?php
$hash = "<script>document.writeln(txthash);</script>";
echo $hash;
?>

To make it more fluent:

Full Example using just Javascript and PHP

<script>
var urlhash = window.location.hash,  //get the hash from url
txthash = urlhash.replace("#", "");  //remove the #

function changehash(a,b){
   window.location.hash = b; //add hash to url
   //alert(b); //alert to test
   location.reload(); //reload page to show the current hash
}
</script>

<?php $hash = "<script>document.writeln(txthash);</script>";?>

<a onclick="changehash(this,'#hash1')" style="text-decoration: underline;cursor: pointer;" >Change to #hash1</a><br/>
<a onclick="changehash(this,'#hash2')" style="text-decoration: underline;cursor: pointer;">Change to #hash2</a><br/> 

<?php echo "This is the current hash: " . $hash; ?> 

I think the hash-value is only used client-side, so you can't get it with php.

you could redirect it with javascript to php though.

We can do it with another approach too, Like first of all get the hash value from js and call the ajax using that parameter and can do whatever we want