URL Rewrite Pattern Matching
This article talks about pattern matches for URL rewriting with the Apache server .htaccess file. You'll learn what the characters "^", "\", and "!" are for.
(If you just want to know how to do simple URL rewriting and don't really care about all the details, see Always www.example.com Or
This is not a comprehensive pattern matching tutorial. Only pattern matching pertinent to URL rewriting is addressed.
Below are 3 lines for URL rewriting. With those 3 lines, whenever a browser requests a page from
RewriteEngine On
RewriteCond %{HTTP_HOST} ^example\.com
RewriteRule (.*) http://www.example.com/$1 [R=301,L]
We will talk about only the RewriteCond line, the middle line in the above example. (URL rewriting may contain several RewriteCond lines.)
The RewriteCond line compares a server value (%{HTTP_HOST} in the example) to a pattern ("^example\.com" in the example).
RewriteCond %{HTTP_HOST} pattern
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"RewriteCond" labels the line as a condition to the URL rewrite.
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"%{HTTP_HOST}" is the domain name in the URL the browser uses to request something from the server.
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"pattern" represents the string of characters that make up a pattern to compare with %{HTTP_HOST}.
If the pattern finds a match within %{HTTP_HOST}, the line succeeds. Otherwise, it fails.
So, let's talk about patterns.
The "^" Character
The caret character ("^") says the beginning of the pattern must match the beginning of %{HTTP_HOST}. Without the caret character, the matching can begin anywhere within %{HTTP_HOST}.
| Pattern: | ^example |
| Matches: | example.com |
| Fails: | www.example.com |
| Fails: | books.example.com |
| Pattern: | example |
| Matches: | example.com |
| Matches: | www.example.com |
| Matches: | books.example.com |
The "\" Character
The backslash character ("\") says the following punctuation character shall be taken literally.
In pattern matching, the period character (".") is a symbol to match any character. When preceded with a backslash character, it is considered a literal period character and not a character with special meaning.
| Pattern: | ^example\.com |
| Matches: | example.com |
| Fails: | examplestuff.com |
| Pattern: | ^example.com |
| Matches: | example.com |
| Matches: | examplescom.com |
The "!" Character
The exclamation mark ("!") at the beginning of the pattern reverses the pattern match result.
If the match would have succeeded, it now fails. If the match would have failed, it now succeeds.
| Pattern: | !^example\.com |
| Fails: | example.com |
| Matches: | www.example.com |
| Matches: | books.example.com |
| Pattern: | ^example\.com |
| Matches: | example.com |
| Fails: | www.example.com |
| Fails: | books.example.com |
| Pattern: | !^www\.example\.com |
| Matches: | example.com |
| Fails: | www.example.com |
| Matches: | books.example.com |
| Pattern: | ^www\.example\.com |
| Fails: | example.com |
| Matches: | www.example.com |
| Fails: | books.example.com |
The characters "^", "\", and "!" have special meaning in pattern matching. You now have a reference to the most common uses of those characters in URL rewrite pattern matching.
Will Bontrager
