How Does Mod_Rewrite Work For Pretty Links?

Rewrite Rules Basics

Rewrite rules are the main part of mod_rewrite's functionality. They let you change URLs before the web server processes them. This is useful for creating user-friendly URLs, redirecting old pages to new ones, or handling complex routing logic.

The basic syntax of a rewrite rule is:

RewriteRule Pattern Substitution [Flags]

• Pattern: A regular expression that matches the incoming URL
• Substitution: The new URL or file path to use
• Flags: Optional parameters that change the rule's behavior

Here are some examples of rewrite rules:

1. Add .php to all requests:

   RewriteRule ^(.*)$ $1.php

2. Redirect all traffic to HTTPS:

   RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]

3. Create a simple pretty URL:

   RewriteRule ^product/([0-9]+)$ product.php?id=$1

Regular Expressions in Mod_Rewrite

Regular expressions (regex) are important in mod_rewrite. They help you create flexible patterns that match various URL structures. With regex, you can capture parts of the URL and use them in the rewritten version.

Some common regex patterns used in mod_rewrite:

• ^: Matches the start of the string
• $: Matches the end of the string
• (.*): Captures any character (except newline) zero or more times
• ([0-9]+): Captures one or more digits

Capturing and replacing URL patterns is a useful feature. For example:

RewriteRule ^article/([0-9]+)/([a-z-]+)$ article.php?id=$1&title=$2

This rule would change a URL like /article/123/my-article-title into article.php?id=123&title=my-article-title.

To learn more about regular expressions, these resources are helpful:

1. Regular-Expressions.info: A guide to regex
2. RegexOne: An interactive tutorial for learning regex
3. RegExr: An online tool for testing regex patterns

Common Rewrite Rule Patterns

Mod_rewrite offers patterns to create pretty links. Here are some common patterns:

1. Rule for appending file extensions:

   RewriteRule ^([^.]+)$ $1.php [L]

   This rule adds a .php extension to URLs without one. For example, /about becomes /about.php.

2. Rule for routing all requests through a single file:

   RewriteCond %{REQUEST_FILENAME} !-f
   RewriteCond %{REQUEST_FILENAME} !-d
   RewriteRule ^(.*)$ index.php?url=$1 [QSA,L]

   This pattern sends all requests to index.php, passing the original URL as a parameter. It's useful for front-controller patterns in frameworks.

3. Use cases for different rule patterns:

• SEO-friendly product pages:

  RewriteRule ^product/([0-9]+)/([a-zA-Z0-9-]+)$ product.php?id=$1&name=$2 [L]

  This changes /product/123/blue-shirt to product.php?id=123&name=blue-shirt.

• Blog post URLs:

  RewriteRule ^blog/([0-9]{4})/([0-9]{2})/([a-zA-Z0-9-]+)$ blog.php?year=$1&month=$2&title=$3 [L]

  This transforms /blog/2023/05/summer-trends to blog.php?year=2023&month=05&title=summer-trends.

Configuring Mod_Rewrite

Mod_rewrite configuration depends on your server setup and needs.

1. Where to place rewrite rules:

• Server configuration file (e.g., httpd.conf):

  • Applies to the entire server
  • Requires server restart to apply changes
  • Example:

    <VirtualHost *:80>
    ServerName example.com
    DocumentRoot /var/www/html
    RewriteEngine On
    RewriteRule ^about$ about.php [L]
    </VirtualHost>

• .htaccess file:

  • Applies to specific directories
  • Changes take effect immediately
  • Example content of .htaccess:

    RewriteEngine On
    RewriteRule ^products/([0-9]+)$ product.php?id=$1 [L]

2. Enabling mod_rewrite in Apache:

To use mod_rewrite, make sure it's enabled in your Apache configuration:

1. Open your Apache configuration file (often httpd.conf or apache2.conf)
2. Find or add this line:

   LoadModule rewrite_module modules/mod_rewrite.so

3. Restart Apache to apply changes

Test your rewrite rules to avoid unexpected behavior on your website.