A simple way to understand mod rewrite

The world of mod rewrite has too many people getting a fish for a day and not enough people learning to fish. Despite mod_rewrite’s quirky and weird syntax, it’s pretty easy to understand if you look at it the right way. My previous post showed how to remove www and index.html with mod rewrite. Here’s a similar script followed by the same exact logic written in pseudo-code, which should be much easier to understand:

# mod_rewrite script
RewriteCond %{REQUEST_URI} ^/media/
RewriteCond %{HTTP_HOST} ^www\.mrcoles\.com [OR]
RewriteCond %{REQUEST_URI} /index\.html$
RewriteRule (.*?)(index\.html)?$ http://mrcoles.com$1 [NE,R=301,L]

# pseudo-code of that script
if (path starts with "/media/") {
    if (host begins with "www.mrcoles.com" or path ends with "/index.html") {
        redirect to "http://mrcoles.com" + the path excluding "index.html"
    }
}

Key ideas:

1. RewriteCond’s are if-statements
2. A RewriteCond creates a code block that doesn’t get closed until we reach a RewriteRule with an [L] flag
3. Multiple RewriteCond if-statement’s, in a row, wrap around each other (AND’ed together), but if you use an [OR] flag, it OR’s the next RewriteCond with the current one
4. Since this forms one code block, you can put separate mod_rewrite scripts before or after it
5. You have to understand regular expressions (out of the scope of this post)

Now that you have built some intuition on how a mod rewrite script gets executed, go out, cast your nets, and become fishers of urls (that are in need of rewriting). On the contrary, if you still don’t have the intuition, sorry… maybe go read up on regular expressions.

For further reading on what the variables are, what the flags do, how the regular expressions work, etc., here’s a pretty comprehensive mod rewrite cheat sheet (the previous link broke, updated!)

Update:

I originally didn’t think to include the simplest syntax, which is a single RewriteRule—or just one if-statement. So, here’s a script and pseudo code example that removes “index.html” from urls with a 301 redirect:

# mod_rewrite script
RewriteRule (.*?/)(index\.html)$ $1 [NE,R=301,L]

# psuedo-code of that script
if (path ends with "/index.html") {
    redirect to the path without "index.html"
}