At its core, mod_rewrite operates through a simple but powerful syntax:

<IfModule mod_rewrite.c>
    RewriteEngine On
    RewriteRule pattern substitution [flags]
</IfModule>

The real magic happens in the pattern matching using PCRE (Perl Compatible Regular Expressions). Here's a basic example that forces HTTPS:

RewriteEngine On
RewriteCond %{HTTPS} !=on
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]

Understanding these PCRE patterns is crucial:

• ^ - Start of string anchor
• $ - End of string anchor
• (.*) - Captures any character (except newline)
• ([a-z]+) - Matches one or more lowercase letters
• \d{4} - Matches exactly 4 digits

Here are practical examples you'll frequently encounter:

1. HTTP to HTTPS Redirect

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

2. Non-www to www

RewriteEngine On
RewriteCond %{HTTP_HOST} !^www\.
RewriteRule ^(.*)$ https://www.%{HTTP_HOST}/$1 [R=301,L]

3. Old URL to New URL

RewriteEngine On
RewriteRule ^old-page\.html$ /new-page.html [R=301,L]

Enable logging in your Apache config:

RewriteLog "/var/log/apache2/rewrite.log"
RewriteLogLevel 3

Use the NC (no case) and OR flags carefully:

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

• Place frequently accessed rules first
• Use [L] flag to stop processing when matched
• Avoid complex regex in high-traffic scenarios
• Consider using Redirect or RedirectMatch for simple cases

Here's a complex rule that handles multiple conditions:

RewriteEngine On
RewriteCond %{REQUEST_URI} !^/static/
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ /index.php?path=$1 [NC,L,QSA]

This rule:

1. Excludes /static/ directory
2. Checks if requested file doesn't exist
3. Checks if requested directory doesn't exist
4. Routes everything else to index.php

Always use 301 (permanent) redirects for moved content:

Redirect 301 /old-path.html /new-path.html

For parameter changes while maintaining SEO value:

RewriteRule ^category/([^/]+)/([^/]+)/?$ /products.php?cat=$1&subcat=$2 [L]

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Apache's mod_rewrite module provides a powerful way to manipulate URLs through rule-based rewriting. The basic syntax follows this structure:

RewriteEngine On
RewriteCond %{REQUEST_URI} pattern [flags]
RewriteRule pattern substitution [flags]

mod_rewrite uses Perl-compatible regular expressions (PCRE). Key patterns include:

• ^ - Start of string
• $ - End of string
• . - Any single character
• * - Zero or more of preceding element
• + - One or more of preceding element
• ? - Makes preceding element optional

HTTP to HTTPS Redirection

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

URL Format Conversion

Convert ?id=123 to /id/123:

RewriteEngine On
RewriteCond %{QUERY_STRING} ^id=([0-9]+)$
RewriteRule ^(.*)$ /id/%1? [R=301,L]

Enable logging for troubleshooting:

RewriteLog "/path/to/rewrite.log"
RewriteLogLevel 3

Keep these in mind:

• Use [L] flag to stop processing further rules
• Place most frequently matched rules first
• Avoid complex regex patterns when possible

Watch out for:

• Infinite redirect loops
• Case sensitivity issues
• Missing RewriteEngine On directive
• Incorrect flag usage (e.g., forgetting [R] for external redirects)

Consider these when mod_rewrite might be overkill:

• Use Redirect or RedirectMatch for simple redirects
• Implement URL routing at application level when possible
• Use Alias for simple path translations