apache - mod_rewrite配置指令RewriteBase

看了好几遍,还是不太清楚.先记下了,有空再看看.apache发展了这么多年,我也用了这么久,就这样一个指令,会用但是不完全了解实际的含义.

RewriteBase Directive

Description:	Sets the base URL for per-directory rewrites
Syntax:	`RewriteBase URL-path`
Default:	`See usage for information.`
Context:	directory, .htaccess
Override:	FileInfo
Status:	Extension
Module:	mod_rewrite

The RewriteBase directive explicitly sets the base URL for per-directory rewrites. As you will see below, RewriteRule can be used in per-directory config files (.htaccess). In such a case, it will act locally, stripping the local directory prefix before processing, and applying rewrite rules only to the remainder. When processing is complete, the prefix is automatically added back to the path. The default setting is; RewriteBase physical-directory-path

When a substitution occurs for a new URL, this module has to re-inject the URL into the server processing. To be able to do this it needs to know what the corresponding URL-prefix or URL-base is. By default this prefix is the corresponding filepath itself. However, for most websites, URLs are NOT directly related to physical filename paths, so this assumption will often be wrong! Therefore, you can use the RewriteBase directive to specify the correct URL-prefix.

If your webserver's URLs are not directly related to physical file paths, you will need to use RewriteBase in every .htaccess file where you want to use RewriteRule directives.

For example, assume the following per-directory config file:

#
#  /abc/def/.htaccess -- per-dir config file for directory /abc/def
#  Remember: /abc/def is the physical path of /xyz, i.e., the server
#            has a 'Alias /xyz /abc/def' directive e.g.
#
RewriteEngine On
#  let the server know that we were reached via /xyz and not
#  via the physical path prefix /abc/def
RewriteBase   /xyz
#  now the rewriting rules
RewriteRule   ^oldstuff/.html$  newstuff.html

In the above example, a request to /xyz/oldstuff.html gets correctly rewritten to the physical file /abc/def/newstuff.html.

For Apache Hackers

The following list gives detailed information about the internal processing steps:

Request:
/xyz/oldstuff.html
Internal Processing:
/xyz/oldstuff.html     -> /abc/def/oldstuff.html  (per-server Alias)
/abc/def/oldstuff.html -> /abc/def/newstuff.html  (per-dir    RewriteRule)
/abc/def/newstuff.html -> /xyz/newstuff.html      (per-dir    RewriteBase)
/xyz/newstuff.html     -> /abc/def/newstuff.html  (per-server Alias)
Result:
/abc/def/newstuff.html

This seems very complicated, but is in fact correct Apache internal processing. Because the per-directory rewriting comes late in the process, the rewritten request has to be re-injected into the Apache kernel. This is not the serious overhead it may seem to be - this re-injection is completely internal to the Apache server (and the same procedure is used by many other operations within Apache).