Apache rewrite rule leading slash

Leading slash first argument: ignored?

What's the syntax difference between

RewriteRule help help.php?q=noslash [L]     #1
RewriteRule /help help.php?q=withslash [L]  #2

If I hit http://local开发者_开发技巧host/help, it goes to #1, if I hit http://localhost//help it still goes to #1.

Am I right in saying the leading slash in the first argument to RewriteRule is essentially ignored?

Leading slash second argument: error?

Also, why doesn't this rewrite rule work?

RewriteRule help /help.php [L]     #1

Putting a leading slash in front of the second arg actually creates a 500 error for the server. Why?

I should note I'm using a .htaccess file to write these rules in

Strangely enough,

RewriteRule   ^/help    help.php?q=2              [L]

The above rule fails and never matches.

This rule:

RewriteRule   ^help      help.php?q=1             [L]

Matches http://localhost/help, http://localhost//help and http://localhost///help

It appears RewriteRule never sees leading slashes of the path, and as TheCoolah said they are collapsed (to 0.. when using a .htaccess file anyway) no matter how many there are.

For the second part of the question,

RewriteRule   ^help    /help.php

I'm getting the answer from Definitive Guide to Apache Mod_rewrite

... a rewrite target that does not begin with http:// or another protocol designator is assumed to be a file system path. File paths that do not begin with a slash are interpreted as being relative to the directory in which the rewriting is taking place.

So /help.php looks in the root of the system for a file called help.php, which on my system it cannot find.

To make /help.php appear as a relative URL (relative to the root of the site) you can use the [PT] directive:

RewriteRule   ^/help    /help.php    [PT]

That directs http://localhost/help to http://localhost/help.php.

Regarding double slashes: Most Web servers silently collapse multiple slashes into a single slash early in the request processing pipeline. This is true for at least Apache, Tomcat and Jetty. Most Unix-based file systems work the same way. If you really want to check for this, you need to do something like:

RewriteCond %{REQUEST_URI} ^(.*)//(.*)$ 

help matches "help" anywhere in the path.

/help matches nothing since the rewriterule directive omits the leading slash for matching purposes (i.e., you must use ^, not / or ^/, to reference the current directory).

(This can be very confusing if you've used %{REQUEST_URI} in rewritecond because %{REQUEST_URI} does begin with a trailing slash. When matching against %{REQUEST_URI}, ^ and ^/ are equivalent and a directory name will always be preceded by a slash character regardless of whether or not it is in the top-level directory.)

The server error is caused by an infinite loop. "help" becomes "/help.php" which is then matched by the same directive that did the rewriting. So, after the first match, "/help.php" becomes "/help.php" infinitely resulting in a URL that can't be resolved.

I believe such loops can be fixed with the end flag (i.e., [end]), but that flag requires Apache 2.3.9+ whereas Apache 2.2 seems to be more common in deployment. It'd probably be better to just fix the regular expression anyway; ^help$ would seem to be the better choice here.

The way RewriteRule works is that if the given regular expression matches any part of the path part of the URL (the part after the host and port but before the query string), then the entire path part is completely replaced with the given substitution. This explains the behaviour you're seeing in the first part of your question.

I'm not sure what could be causing the 500 errors on the second part; maybe the collapsing of doubled slashes doesn't happen after the rewrite engine has run and then generates a server error.

The reason for the 500 Error is an infinitive Loop:

• help gets rewritten to /help
• /help gets stripped to help
• help gets rewritten to /help etc. until the MaxRewrites limit is hit -> 500

Whereas if the rule rewrites help to help, Apache is smart enough to abort rewriting at that point.