.htaccess mod rewrite issue

Experts Needed!

[Roel]

I hope some of the .htaccess experts can fix this one;

I had many url's that look like this:

example.com/subdir1/abc/
example.com/subdir1/xyz/
example.com/subdir1/
example.com/subdir2/abc/
example.com/subdir2/xyz/
example.com/subdir2/
example.com/subdir2/subdir3/abc/
example.com/subdir2/subdir3/abc/
example.com/subdir2/subdir3/

That now look like this:

example.com/abc/subdir1/
example.com/xyz/subdir1/
example.com/subdir1/
example.com/abc/subdir2/
example.com/xyz/subdir2/
example.com/subdir2/
example.com/abc/subdir2/subdir3/
example.com/xyz/subdir2/subdir3/
example.com/subdir2/subdir3/

So all URL's with abc and xyz ONLY have changed abc and xyz has moved to the front. Other URL's have not changed.

How can I write a mod_rewrite so that all these are changed automatically?

[edited by: Roel at 5:31 am (utc) on Aug. 2, 2007]

[jdMorgan]

How you do this, and whether it's even possible to do it, depends on how much the "xyz" and "subdir" parts of the URL can change -- In other words, it depends on how many different cases must be handled.

The main problem is recognizing a URL that needs to be rewritten from one that does not. Therefore, you have to pattern-match at least part of the URL based on prior knowledge of what its values can be, so that you can recognize that it needs to be rewritten.

Jim

[Roel]

Hi Jim

Thanks for your help.

There are around 10 possibilities for abc/xyz

let's say they are 111,222,333,444,555,666,777,888,999,000

Then how would I write this rewrite?

Thanks again!

[jdMorgan]

Well, it also depends on how the subdirs can change as well. These concepts of "degrees of freedom of variability", URL-classes, or URL taxonomy are a bit tough to get across. But the basis of the question lies in the capabilities of the regular-expressions-based pattern-matching used by mod_rewrite (and many modern scripting languages). Regular expressions can detect:

uppercase alphabetic characters [A-Z]

lowercase alphabetic characters [a-z]

mixed-case alphabetic characters [A-Za-z]

numerals [0-9]

punctuation [`~!@#$%^&*()_+\-={}\[\]¦\\:";'<>?,./]

any single character .

combinations of the above types [a-z0-9_]

It can also detect quantities of those characters:

zero or one ?

zero or more *

one (literal character)

one or more +

any fixed number {3}

a minimum number {3,}

a maximum number {,9}

a range of numbers between minimum and maximum inclusive {3,9}

These capabilities, when combined, allow you to "classify" URLs. Just as an example, the pattern:
^[a-z]{2,8}[0-9]-p-[0-9]{4,}[abcABC]?/$
describes a URL-path that starts with two to eight lowercase characters, followed by a single digit 0 through 9, followed by "-p-", followed by a minimum of 4 digits 0 through 9, followed by an optional character a, b, c, A, B, or C, and ending with a trailing slash.

Any URL-path that matches this description will be accepted -- i.e. the rule based on this pattern will be invoked. Any URL-path that does not match this pattern will be rejected, and the rule won't run.

You must classify *all* of your URL-paths that need to be rewritten using this system. If there are too many URL-paths to consider, then you may wish to classify all of the URL-paths that *should not* be rewritten -- again using this system. If you cannot classify them this way, then the problem cannot be solved by using a generalized regular expressions pattern in mod_rewrite, and will have to be solved on a case-by-case basis, that is, one rule for each specific URL-path.

So here's one level of classification. This is a literal substitution only -- The pattern is literal and describes only one URL-path; Only that specific URL-path will be rewritten:

RewriteRule ^subdir1/abc/$ /abc/subdir1/ [L]

Now here's an almost-completely-generic rule -- one that is likely to rewrite far too many URLs, giving you undesired side effects:

RewriteRule ^([^/]+)/([^/]+)/$ $2/$1/ [L]

Here the numeric variables $1 and $2 refer back to (they "back-reference") the first and second parenthesized subpatterns. Each of those patterns "[^/]+" will match one or more characters that are not slashes.

So if the URL-path "subdir1/abc/" is requested, then $1 becomes "subdir1" and $2 becomes "abc". The variables are then used on the right side to re-assemble these two URL-path-parts in reverse to form the new URL-path, "abc/subdir1/"

However, this second rule will match *any* URL-path with the form
<non-slash-characters> / <non-slash-characters> /
which is probably not what you want. So you'll likely need to develop a more-specific pattern or patterns, based on your knowledge of the URL-classes you need to rewrite -- both now and (if you're actively adding URLs) in the future.

Jim

[edited by: jdMorgan at 9:20 pm (utc) on Aug. 5, 2007]

[Roel]

Hi Jim

Wow that was quite a bit. I started playing with it, but the issue for me is that I am using wordpress already. So this is my current .htacess:

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME}!-f
RewriteCond %{REQUEST_FILENAME}!-d
RewriteRule . /index.php [L]
</IfModule>

I tried doing the following:

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{THE_REQUEST} ^.*/abc/.*$ [NC]
RewriteRule ^([^/]+)/abc/$ abc/$1/ [L]
RewriteCond %{REQUEST_FILENAME}!-f
RewriteCond %{REQUEST_FILENAME}!-d
RewriteRule . /index.php [L]
</IfModule>

But that gives me a 404 on example.com/abc/

Any ideas what I am doing wrong here?

[jdMorgan]

RewriteCond %{THE_REQUEST} ^.*/abc/.*$ [NC]
RewriteRule ^([^/]+)/abc/$ abc/$1/ [L]

In this case, the RewriteCond is redundant.

Also, the rule will rewrite the client-requested URL-path "<something>/abc/" to the file /abc/<something>/

Your test URL is missing the "<something/" part, so this rule won't be applied.

However, since the following rule should rewrite all requested URLs that don't resolve to an existing file or directory, passing them to WordPress, I don't see how you're getting a 404 unless the WordPress rewrite isn't working either, or this code is not in the right directory.

Jim