PHP .htaccess -> pretty url (in reverse) - php

Question

I know how to make URL's rewrite, for example:
www.example.com/index.php?id=1&cat=3 to www.example.com/1/3/ (or whatever). I know that.
What I don't know is how on earth to change my whole links in all pages to link to pretty URL's. All my site's links are old fashion (<a href="index.php?id=1&cat=2">) and there are many.
I`m asking if someone has an idea or know how to automaticaly redirect to that pretty url if the user click on index.php?id=1. (Almost like this site Stackoverflow if you change title in the url).
So my presumtions are...
Use .htaccess to read the index.php?id=1&cat=2 to rewrite index/1/3 that itself interprets again (strange)
a php file to do the redirects that htaccess rewrites back to original...
Conclusion: change <a href="index.php?id=1&....."> automaticaly to index/1/2
SOLVED
Options +FollowSymLinks
RewriteEngine On
RewriteBase /
##################################
# This turns index.php?id=1&cat=2 into index/1/2 and then back 'transparent' into index.php?id=1&cat=2 if you have old fashioned
# links in your site and don't want to change them :)
# Avoid mod_rewrite infinite loops
# This is critical if you want to use this code
RewriteCond %{ENV:REDIRECT_STATUS} 200
RewriteRule .* - [L]
# Hard-rewrite ("[R]") to "friendly" URL.
# Needs RewriteCond to match original querystring.
# Uses "?" in target to remove original querystring,
# and "%n" backrefs to move its components.
# Target must be a full path as it's a hard-rewrite.
RewriteCond %{QUERY_STRING} ^id=(\d+)&cat=(\d+)$
RewriteRule ^index.php$ http://localhost/index/%1/%2/? [L,R]
# Soft-rewrite from "friendly" URL to "real" URL.
# Transparent to browser.
# Won't re-trigger the above rewrite, though I'm
# not really sure why! The order of the rules
# doesn't seem to make a difference.
RewriteRule ^index/(\d+)/(\d+)/$ index.php?id=$1&cat=$2 [L]

Answer 1

RewriteEngine on
# Prevents browser looping, which does seem
# to occur in some specific scenarios. Can't
# explain the mechanics of this problem in
# detail, but there we go.
RewriteCond %{ENV:REDIRECT_STATUS} 200
RewriteRule .* - [L]
# Hard-rewrite ("[R]") to "friendly" URL.
# Needs RewriteCond to match original querystring.
# Uses "?" in target to remove original querystring,
# and "%n" backrefs to move its components.
# Target must be a full path as it's a hard-rewrite.
RewriteCond %{QUERY_STRING} ^id=(\d+)&cat=(\d+)$
RewriteRule ^index\.php$ http://example.com/index/%1/%2/? [L,R]
# Soft-rewrite from "friendly" URL to "real" URL.
# Transparent to browser.
RewriteRule ^index/(\d+)/(\d+)/$ /index.php?id=$1&cat=$2
Of course, ideally, you'd just fix your links, and then you'd only require the soft-rewrite. :)
Tested with Apache/2.2.3. I think I made up the terms "hard-rewrite" and "soft-rewrite".

Answer 2

Why not just change your index.php file to do it? You could theoretically do a little more error checking that way, allowing for the variables to be in any order and still get routed to the correct end location.
<?php
// Permanent redirection
header("HTTP/1.1 301 Moved Permanently");
header("Location: http://www.example.com/{$_GET['id']}/{$_GET['cat']}");
I didn't do any error checking here, but wanted to give a base example.
On second thought I guess this is adding in functionality to the index.php file which you then want to use for your application itself, so perhaps it would end up confusing the functionality in the code.