Mod_Rewrite Example, site.tld/USER

[arnage]

This simply changes the dynamic parts of url, such is page.php?var=$user.

First is mod_rewrite in .htaccess file:

RewriteEngine on
Options +FollowSymLinks
RewriteBase /
RewriteRule ^([0-9Aa-zZ]+)/$ page.php?var=$1 [L]

This means that from the part $1 will be token if the content is lower-upper case letters and numbers and set it after RewriteBase which is domain.

Next is setting or changing the links through the script such as ./page/var instead ./page.php?var=var

But if you have done script and just want to change this way, for example, for users, it is much easier to write a redirect page to avoid editing the whole script.
That is pretty much like this.
Make redirect.php with:

$url = !empty($_GET['query']) ? (preg_match('/^[a-z0-9]+$/iD', $_GET['query']) ? $_GET['query'] : null) : null;
if (isset($url)) {

    $url = trim($url);
    if (get_magic_quotes_gpc()) $url = stripslashes($url);
    $query = mysql_query('SELECT * FROM `users` WHERE `nick` = "'.mysql_real_escape_string($url).'" LIMIT 1');
    if (mysql_num_rows($query)) {

        $id = mysql_fetch_array($query);
        $go = (int) $id['id'];

        header('Location: ./index.php?id='.$go.'');
        exit;

    } else {
        header('Location: /');
        exit;
    }
} else { exit('Redirect Error'); } 

With .htaccess code:

RewriteEngine on
Options +FollowSymLinks
RewriteBase /
RewriteRule ^([0-9Aa-zZ]+)/$ redirect.php?query=$1 [L]

Thats it. And if you have some other GET vars across this rewrite, you would have to add it in both parts.

[Ghost]

here is my way of making topic links identical to coding-talk topic links.

RewriteRule ^f([0-9]+)/.*?-([0-9]+)/index([0-9]+).html/$ topic.php?cid=$1&tid=$2&page=$3 [L]
RewriteRule ^f([0-9]+)/.*?-([0-9]+)/index([0-9]+).html$ topic.php?cid=$1&tid=$2&page=$3 [L]
//
//
// 

then function to turn links to seo friendly.

function SEO_Friendly($mysqli, $SEO_Friendly, $Data) {
if($SEO_Friendly == 'On') {
if(preg_match('/topic.php\?cid=(\w+)&tid=(\w+)&page=(\w+)/i', $Data, $matches)) {
$query = $mysqli->query('SELECT * FROM `topics` WHERE id="'.$matches[2].'" LIMIT 1') or die($mysqli->error);
if($query->num_rows > 0) {
while($Row = $query->fetch_assoc()) { $title = str_replace(' ', '-', $Row['topic_title']); }
}
$query->free();
$Data = preg_replace('/topic.php\?cid=(\w+)&tid=(\w+)&page=(\w+)/i', 'f\\1/'.$title.'-\\2/index\\3.html', $Data);
return $Data;
}
} else {
return $Data;
}
return $Data;
}

//
// 

used like this:

echo '<a href="'.SEO_Friendly($mysqli, $SEO_Friendly, 'topic.php?cid='.$cid.'&amp;tid='.$tid.'&amp;page='.$page).'#'.$Row2['id'].'">#'.$Row2['id'].'</a>'."\r\n";
//
// 

add this to config:

$SEO_Friendly = 'On';
//
//
// 

results if seo option is ON:
site.tld/f2/title-here-25/index1.html#92

result if seo option is OFF:
site.tld/topic.php?cid=2&tid=25&page=1#92

seo link description:
f2 = category/forum (2)
title-here-25 = topic name AND topic id (25)
index1.html = page (1) will change to index2, index3 etc
#92 = topic post id (92) for jumping to post