Apache httpd/mod rewrite

Syntax

The Apache manual says:

• RewriteRule <Pattern> <Substitution> [<flags>]
• RewriteCond <TestString> <CondPattern> [<flags>]
• RewriteBase <URL-path>

I think I still don't really understand RewriteBase. Apparently it does need to refer to a path that actually exists, rather than a mapped path. If the path doesn't exist, Apache will log a "core:alert" error saying "RewriteBase: argument is not a valid URL".

RewriteRule

Arguments:

• Pattern is a perl compatible regular expression, matched against:
  • if VirtualHost context: the part of the URL after the hostname and port, and before the query string (e.g. "/app1/index.html").
  • if per-directory context (Directory and .htaccess): the partial path to the Directory or .htaccess file
    • e.g. a request of "/app1/index.html" may result in comparison against "app1/index.html" or "index.html" depending on where the RewriteRule is defined.
    • The directory path where the rule is defined is stripped from the currently mapped filesystem path before comparison (up to and including a trailing slash). The net result of this per-directory prefix stripping is that rules in this context only match against the portion of the currently mapped filesystem path "below" where the rule is defined.
• Substitution may be:
  • URL-path: A DocumentRoot-relative path to the intended target
  • Absolute-URL: if the hostname matches the current host, the scheme and hostname are stripped out and the resulting path is treated as a URL-path. Otherwise, an external redirect is performed.
  • filesystem-path (only in VirtualHost)

manual examples

The following apply inside the per-directory configuration* for /somepath for request GET /somepath/localpath/pathinfo

(*/physical/path/to/somepath/.htaccess, with RewriteBase "/somepath")

Given Rule	Resulting Substitution
^localpath(.*) otherpath$1	/somepath/otherpath/pathinfo
^localpath(.*) otherpath$1 [R]	http://thishost/somepath/otherpath/pathinfo via external redirection
^localpath(.*) otherpath$1 [P]	doesn't make sense, not supported
^localpath(.*) /otherpath$1	/otherpath/pathinfo
^localpath(.*) /otherpath$1 [R]	http://thishost/otherpath/pathinfo via external redirection
^localpath(.*) /otherpath$1 [P]	doesn't make sense, not supported
^localpath(.*) http://thishost/otherpath$1	/otherpath/pathinfo
^localpath(.*) http://thishost/otherpath$1 [R]	http://thishost/otherpath/pathinfo via external redirection
^localpath(.*) http://thishost/otherpath$1 [P]	doesn't make sense, not supported
^localpath(.*) http://otherhost/otherpath$1	http://otherhost/otherpath/pathinfo via external redirection
^localpath(.*) http://otherhost/otherpath$1 [R]	http://otherhost/otherpath/pathinfo via external redirection (the [R] flag is redundant)
^localpath(.*) http://otherhost/otherpath$1 [P]	http://otherhost/otherpath/pathinfo via internal proxy

The following apply inside per-server configuration* for request GET /somepath/pathinfo:

(*VirtualHost in httpd.conf or presumably /etc/apache2/sites-enabled/sitename.conf)

Given Rule	Resulting Substitution
^/somepath(.*) otherpath$1	invalid, not supported
^/somepath(.*) otherpath$1 [R]	invalid, not supported
^/somepath(.*) otherpath$1 [P]	invalid, not supported
^/somepath(.*) /otherpath$1	/otherpath/pathinfo
^/somepath(.*) /otherpath$1 [R]	http://thishost/otherpath/pathinfo via external redirection
^/somepath(.*) /otherpath$1 [P]	doesn't make sense, not supported
^/somepath(.*) http://thishost/otherpath$1	/otherpath/pathinfo
^/somepath(.*) http://thishost/otherpath$1 [R]	http://thishost/otherpath/pathinfo via external redirection
^/somepath(.*) http://thishost/otherpath$1 [P]	doesn't make sense, not supported
^/somepath(.*) http://otherhost/otherpath$1	http://otherhost/otherpath/pathinfo via external redirection
^/somepath(.*) http://otherhost/otherpath$1 [R]	http://otherhost/otherpath/pathinfo via external redirection (the [R] flag is redundant)
^/somepath(.*) http://otherhost/otherpath$1 [P]	http://otherhost/otherpath/pathinfo via internal proxy

Notes

• Woozle's: User:Woozle/mod_rewrite