mod_rewrite.c
file, with
Apache 1.2 and later. It provides
a rule-based rewriting engine to rewrite requested URLs on the fly.
mod_rewrite
is not compiled into the server by
default. To use mod_rewrite
you have to enable the following
line in the server build Configuration file:
Module rewrite_module mod_rewrite.o
It supports an unlimited number of additional rule conditions (which can operate on a lot of variables, including HTTP headers) for granular matching and external database lookups (either via plain text tables, DBM hash files or external processes) for advanced URL substitution.
It operates on the full URLs (including the PATH_INFO part) both in per-server context (httpd.conf) and per-dir context (.htaccess) and even can generate QUERY_STRING parts on result. The rewritten result can lead to internal sub-processing, external request redirection or to internal proxy throughput.
The latest version can be found on
http://www.engelschall.com/sw/mod_rewrite/
Copyright © 1996 The Apache Group, All rights reserved.
Copyright © 1996 Ralf S. Engelschall, All rights reserved.
Written for The Apache Group by
Ralf S. Engelschall
rse@engelschall.com
http://www.engelschall.com/~rse
RewriteEngine
{on,off
}RewriteEngine off
The RewriteEngine directive enables or disables the
runtime rewriting engine. If it is set to off
this module does
no runtime processing at all. It does not even update the SCRIPT_URx
environment variables.
Use this directive to disable the module instead of commenting out all RewriteRule directives!
RewriteOptions
Syntax: RewriteOptions
Option ...
Default: -None-
Context: server config, virtual host, per-directory config
The RewriteOption directive sets some special options for the current per-server or per-directory configuration. The Option strings can be one of the following:
inherit
'
RewriteLog
Syntax: RewriteLog
Filename
Default: -None-
Context: server config, virtual host
The RewriteLog directive sets the name of the file to which the server logs any rewriting actions it performs. If the name does not begin with a slash ('/') then it is assumed to be relative to the Server Root. The directive should occur only once per server config.
To disable the logging of rewriting actions it is not recommended
to set Filename
to /dev/null , because although the rewriting engine does
not create output to a logfile it still creates the logfile
output internally. This will slow down the server with no advantage to the
administrator!
To disable logging either remove or comment out the
RewriteLog directive or use RewriteLogLevel 0!
|
Example:
RewriteLog "/usr/local/var/apache/logs/rewrite.log"
RewriteLogLevel
Syntax: RewriteLogLevel
Level
Default: RewriteLogLevel 0
Context: server config, virtual host
The RewriteLogLevel directive set the verbosity level of the rewriting logfile. The default level 0 means no logging, while 9 or more means that practically all actions are logged.
To disable the logging of rewriting actions simply set Level to 0. This disables all rewrite action logs.
Notice: Using a high value for Level will slow down your Apache server dramatically! Use the rewriting logfile only for debugging or at least at Level not greater than 2! |
Example:
RewriteLogLevel 3
RewriteMap
Syntax: RewriteMap
Mapname {txt,dbm,prg}:
Filename
Default: not used per default
Context: server config, virtual host
The RewriteMap directive defines an external Rewriting Map which can be used inside rule substitution strings by the mapping-functions to insert/substitute fields through a key lookup.
The Mapname is the name of the map and will be used to specify a mapping-function for the substitution strings of a rewriting rule via
When such a directive occurs the map Mapname is consulted and the key LookupKey is looked-up. If the key is found, the map-function directive is substituted by SubstValue. If the key is not found then it is substituted by DefaultValue.${
Mapname:
LookupKey|
DefaultValue}
The Filename must be a valid Unix filepath, containing one of the following formats:
This is a ASCII file which contains either blank lines, comment lines (starting with a '#' character) or
MatchingKey SubstValuepairs - one per line. You can create such files either manually, using your favorite editor, or by using the programs mapcollect and mapmerge from the support directory of the mod_rewrite distribution.
To declare such a map prefix, Filename with a txt:
string as in the following example:
# # map.real-to-user -- maps realnames to usernames # Ralf.S.Engelschall rse # Bastard Operator From Hell Dr.Fred.Klabuster fred # Mr. DAU |
RewriteMap real-to-host txt:/path/to/file/map.real-to-user |
This is a binary NDBM format file containing the
same contents as the Plain Text Format files. You can create
such a file with any NDBM tool or with the dbmmanage program
from the support directory of the Apache distribution.
To declare such a map prefix Filename with a
This is a Unix executable, not a lookup file. To create it you can use
the language of your choice, but the result has to be a run-able Unix
binary (i.e. either object-code or a script with the
magic cookie trick '#!/path/to/interpreter' as the first line).
This program gets started once at startup of the Apache servers and then
communicates with the rewriting engine over its stdin and
stdout file-handles. For each map-function lookup it will
receive the key to lookup as a newline-terminated string on
stdin. It then has to give back the looked-up value as a
newline-terminated string on stdout or the four-character string
``NULL'' if it fails (i.e. there is no corresponding value
for the given key). A trivial program which will implement a 1:1 map
(i.e. key == value) could be:
But be very careful:
To declare such a map prefix Filename with a dbm:
string.
#!/usr/bin/perl
$| = 1;
while (<STDIN>) {
# ...here any transformations
# or lookups should occur...
print $_;
}
prg:
string.
For plain text and DBM format files the looked-up keys are cached in-core until the mtime of the mapfile changes or the server does a restart. This way you can have map-functions in rules which are used for every request. This is no problem, because the external lookup only happens once! |
RewriteBase
Syntax: RewriteBase
BaseURL
Default: default is the physical directory path
Context: per-directory config
The RewriteBase directive explicitly sets the base URL for per-directory rewrites. As you will see below, RewriteRule can be used in per-directory config files (.htaccess). There it will act locally, i.e. the local directory prefix is stripped at this stage of processing and your rewriting rules act only on the remainder. At the end it is automatically added.
When a substitution occurs for a new URL, this module has to re-inject the URL into the server processing. To be able to do this it needs to know what the corresponding URL-prefix or URL-base is. By default this prefix is the corresponding filepath itself. But at most web-sites URLs are NOT directly related to physical filename paths, so this assumption will be usually be wrong! There you have to use the RewriteBase directive to specify the correct URL-prefix.
So, if your web-server's URLs are not directly related to physical file paths, you have to use RewriteBase in every .htaccess files where you want to use RewriteRule directives. |
Example:
Assume the following per-directory config file:
# # /abc/def/.htaccess -- per-dir config file for directory /abc/def # Remember: /abc/def is the physical path of /xyz, i.e. the server # has a 'Alias /xyz /abc/def' directive e.g. # RewriteEngine On # let the server know that we are reached via /xyz and not # via the physical path prefix /abc/def RewriteBase /xyz # now the rewriting rules RewriteRule ^oldstuff\.html$ newstuff.htmlIn the above example, a request to /xyz/oldstuff.html gets correctly rewritten to the physical file /abc/def/newstuff.html.
For the 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.htmlThis seems very complicated but is the correct Apache internal processing, because the per-directory rewriting comes too late in the process. So, when it occurs the (rewritten) request has to be re-injected into the Apache kernel! BUT: While this seems like a serious overhead, it really isn't, because this re-injection happens fully internal to the Apache server and the same procedure is used by many other operations inside Apache. So, you can be sure the design and implementation is correct.
RewriteCond
Syntax: RewriteCond
TestString CondPattern
Default: -None-
Context: server config, virtual host, per-directory config
The RewriteCond directive defines a rule condition. Precede a
RewriteRule directive with one ore more
TestString is a string which contains server-variables of the form
HTTP_USER_AGENT
REMOTE_ADDR
DOCUMENT_ROOT
TIME_YEAR
API_VERSION
Special Notes:
CondPattern is the condition pattern, i.e. a regular expression
which gets applied to the current instance of the TestString, i.e.
TestString gets evaluated and then matched against
CondPattern.
Remember: CondPattern is a standard
Extended Regular Expression with some additions:
Notice: All of these tests can also be prefixed by a not ('!') character
to negate their meaning.
Additionally you can set special flags for CondPattern by appending
Example:
The RewriteRule directive is the real rewriting workhorse. The
directive can occur more than once. Each directive then defines one single
rewriting rule. The definition order of these rules is
important, because this order is used when applying the rules at
run-time.
Pattern can be (for Apache 1.1.x a System
V8 and for Apache 1.2.x a POSIX) regular expression
which gets applied to the current URL. Here ``current'' means the value of the
URL when this rule gets applied. This may not be the original requested
URL, because there could be any number of rules before which already matched
and made alterations to it.
Some hints about the syntax of regular expressions:
Additionally the NOT character ('!') is a possible pattern
prefix. This gives you the ability to negate a pattern; to say, for instance: ``if
the current URL does NOT match to this pattern''. This can be used
for special cases where it is better to match the negative pattern or as a
last default rule.
Substitution of a rewriting rule is the string
which is substituted for (or replaces) the original URL for which
Pattern matched. Beside plain text you can use
As already mentioned above, all the rewriting rules are applied to the
Substitution (in the order of definition in the config file). The
URL is completely replaced by the Substitution and the
rewriting process goes on until there are no more rules (unless explicitly
terminated by a
There is a special substitution string named '-' which means:
NO substitution! Sounds silly? No, it is useful to provide rewriting
rules which only match some URLs but do no substitution, e.g. in
conjunction with the C (chain) flag to be able to have more than one
pattern to be applied before a substitution occurs.
Remember: An unconditional external redirect to your own server will
not work with the prefix http://thishost because of this feature.
To achieve such a self-redirect, you have to use the R-flag (see
below).
Additionally you can set special flags for Substitution by appending
Use the following rule for your decision: whenever you prefix some URLs
with CGI-scripts to force them to be processed by the CGI-script, the
chance is high that you will run into problems (or even overhead) on sub-requests.
In these cases, use this flag.
Notice: You have to use this flag if you want to intermix directives
of different modules which contain URL-to-filename translators. The
typical example is the use of mod_alias and
mod_rewrite..
There is one exception: If a substitution string starts with
``http://'' then the directory prefix will be not added and a
external redirect or proxy throughput (if flag P is used!) is forced!
Here are all possible substitution combinations and their meanings:
Inside per-server configuration (httpd.conf)
Inside per-directory configuration for /somepath
Example:
We take the rewrite mapfile from above and save it under
%{ NAME_OF_VARIABLE }
where NAME_OF_VARIABLE can be a string
of the following list:
HTTP headers:
HTTP_REFERER
HTTP_COOKIE
HTTP_FORWARDED
HTTP_HOST
HTTP_PROXY_CONNECTION
HTTP_ACCEPT
connection & request:
REMOTE_HOST
REMOTE_USER
REMOTE_IDENT
REQUEST_METHOD
SCRIPT_FILENAME
PATH_INFO
QUERY_STRING
AUTH_TYPE
server internals:
SERVER_ADMIN
SERVER_NAME
SERVER_PORT
SERVER_PROTOCOL
SERVER_SOFTWARE
SERVER_VERSION
system stuff:
TIME_MON
TIME_DAY
TIME_HOUR
TIME_MIN
TIME_SEC
TIME_WDAY
specials:
THE_REQUEST
REQUEST_URI
REQUEST_FILENAME
These variables all correspond to the similar named HTTP MIME-headers, C
variables of the Apache server or struct tm fields of the Unix
system.
Treats the TestString as a pathname and
tests if it exists and is a directory.
Treats the TestString as a pathname and
tests if it exists and is a regular file.
Treats the TestString as a pathname and
tests if it exists and is a regular file with size greater then zero.
Treats the TestString as a pathname and
tests if it exists and is a symbolic link.
as the third argument to the RewriteCond directive. Flags
is a comma-separated list of the following flags:
[
flags]
nocase|NC
' (no case)
This makes the condition test case-insensitive, i.e. there is
no difference between 'A-Z' and 'a-z' both in the expanded
TestString and the CondPattern.
ornext|OR
' (or next condition)
Use this to combine rule conditions with a local OR instead of the
implicit AND. Typical example:
Without this flag you had to write down the cond/rule three times.
RewriteCond %{REMOTE_HOST} ^host1.* [OR]
RewriteCond %{REMOTE_HOST} ^host2.* [OR]
RewriteCond %{REMOTE_HOST} ^host3.*
RewriteRule ...some special stuff for any of these hosts...
To rewrite the Home-page of a site according to the ``User-Agent:''
header of the request, you can use the following:
Interpretation: If you use Netscape Navigator as your browser (which identifies
itself as 'Mozilla'), then you get the max homepage, which includes
Frames, etc. If you use the Lynx browser (which is Terminal-based), then you
get the min homepage, which contains no images, no tables, etc. If you
use any other browser you get the standard homepage.
RewriteCond %{HTTP_USER_AGENT} ^Mozilla.*
RewriteRule ^/$ /homepage.max.html [L]
RewriteCond %{HTTP_USER_AGENT} ^Lynx.*
RewriteRule ^/$ /homepage.min.html [L]
RewriteRule ^/$ /homepage.std.html [L]
RewriteRule
Syntax: RewriteRule
Pattern Substitution
Default: -None-
Context: server config, virtual host, per-directory config
^
Start of line
$
End of line
.
Any single character
[
chars]
One of chars
[^
chars]
None of chars
?
0 or 1 of the preceding char
*
0 or N of the preceding char
+
1 or N of the preceding char
\
char escape that specific char
(e.g. for specifying the chars ".[]()
" etc.)
(
string)
Grouping of chars (the Nth group can be used on the RHS with $
N)
Notice! When using the NOT character to negate a pattern you cannot
have grouped wildcard parts in the pattern. This is impossible because when
the pattern does NOT match, there are no contents for the groups. In
consequence, if negated patterns are used, you cannot use $N in the
substitution string!
Back-references are $N
)
%{VARNAME}
)
${mapname:key|default}
)
$
N (N=1..9) identifiers which
will be replaced by the contents of the Nth group of the matched
Pattern. The server-variables are the same as for the
TestString of a RewriteCond directive. The
mapping-functions come from the RewriteMap directive and are
explained there. These three types of variables are expanded in the order of
the above list.
L
flag - see below).
Notice: There is a special feature. When you prefix a substitution
field with http://thishost[:thisport] then
mod_rewrite automatically strips it out. This auto-reduction on
implicit external redirect URLs is a useful and important feature when
used in combination with a mapping-function which generates the hostname
part. Have a look at the first example in the example section below to
understand this.
as the third argument to the RewriteRule directive. Flags is a
comma-separated list of the following flags:
[
flags]
redirect|R
' (force redirect)
Prefix Substitution
with http://thishost/
(which makes the new URL a URI) to
force a external redirection. Use it for rules which should
canonicalize the URL and gives it back to the client, e.g. translate
``/~
'' into ``/u/
'' or always append a slash to
/u/
user, etc.
Notice: When you use this flag, make sure that the
substitution field is a valid URL! If not, you are redirecting to an invalid
location!
proxy|P
' (force proxy)
This flag forces the substitution part to be internally forced as a proxy
request and immediately (i.e. rewriting rule processing stops here) put
through the proxy module. You have to make sure that the substitution
string is a valid URI (e.g. typically http://) which can
be handled by the Apache proxy module. If not you get an error from
the proxy module. Use this flag to achieve a more powerful implementation
of the mod_proxy directive ProxyPass, to map
some remote stuff into the name-space of the local server.
last|L
' (last rule)
Stop the rewriting process here and
don't apply any more rewriting rules. This corresponds to the Perl
last
command or the break
command from the C
language. Use this flag to prevent the currently rewritten URL from being
rewritten further by following rules which may be wrong. For
example, use it to rewrite the root-path URL ('/
') to a real
one, e.g. '/e/www/
'.
next|N
' (next round)
Re-run the rewriting process (starting again with the first rewriting
rule). Here the URL to match is again not the original URL but the URL
from the last rewriting rule. This corresponds to the Perl
next
command or the continue
command from the C
language. Use this flag to restart the rewriting process, i.e. to
immediately go to the top of the loop.
But be careful not to create a deadloop!
chain|C
' (chained with next rule)
This flag chains the current rule with the next rule (which itself can
also be chained with its following rule, etc.). This has the following
effect: if a rule matches, then processing continues as usual, i.e. the
flag has no effect. If the rule does not match, then all following
chained rules are skipped. For instance, use it to remove the
``.www'' part inside a per-directory rule set when you let an
external redirect happen (where the ``.www'' part should not to
occur!).
type|T
=mime-type' (force MIME type)
Force the MIME-type of the target file to be mime-type. For
instance, this can be used to simulate the old mod_alias
directive ScriptAlias which internally forces all files inside
the mapped directory to have a MIME type of
``application/x-httpd-cgi''.
nosubreq|NS
' (used only if no internal sub-request)
This flag forces the rewriting engine to skip a rewriting rule if the
current request is an internal sub-request. For instance, sub-requests
occur internally in Apache when mod_include tries to find out
information about possible directory default files (index.xxx).
On sub-requests it is not always useful and even sometimes causes a failure to
if the complete set of rules are applied. Use this flag to exclude some rules.
passthrough|PT
' (pass through to next handler)
This flag forces the rewriting engine to set the uri
field
of the internal request_rec
structure to the value
of the filename
field. This flag is just a hack to be able
to post-process the output of RewriteRule directives by
Alias, ScriptAlias, Redirect, etc. directives
from other URI-to-filename translators. A trivial example to show the
semantics:
If you want to rewrite /abc to /def via the rewriting
engine of mod_rewrite and then /def to /ghi
with mod_alias:
RewriteRule ^/abc(.*) /def$1 [PT]
Alias /def /ghi
If you omit the PT flag then mod_rewrite
will do its job fine, i.e. it rewrites uri=/abc/... to
filename=/def/... as a full API-compliant URI-to-filename
translator should do. Then mod_alias comes and tries to do a
URI-to-filename transition which will not work.
For the Apache hackers:
If the current Apache API had a
filename-to-filename hook additionally to the URI-to-filename hook then
we wouldn't need this flag! But without such a hook this flag is the
only solution. The Apache Group has discussed this problem and will
add such hooks into Apache version 2.0.
skip|S
=num' (skip next rule(s))
This flag forces the rewriting engine to skip the next num rules
in sequence when the current rule matches. Use this to make pseudo
if-then-else constructs: The last rule of the then-clause becomes
a skip=N where N is the number of rules in the else-clause.
(This is not the same as the 'chain|C' flag!)
Remember: Never forget that Pattern gets applied to a complete URL
in per-server configuration files. But in per-directory configuration
files, the per-directory prefix (which always is the same for a specific
directory!) gets automatically removed for the pattern matching and
automatically added after the substitution has been done. This feature is
essential for many sorts of rewriting, because without this prefix stripping
you have to match the parent directory which is not always possible.
Notice! To enable the rewriting engine for per-directory configuration files
you need to set ``RewriteEngine On'' in these files and
``Option FollowSymLinks'' enabled. If your administrator has
disabled override of FollowSymLinks for a user's directory, then
you cannot use the rewriting engine. This restriction is needed for
security reasons.
for request ``GET /somepath/pathinfo'':
Given Rule Resulting Substitution
---------------------------------------------- ----------------------------------
^/somepath(.*) otherpath$1 not supported, because invalid!
^/somepath(.*) otherpath$1 [R] not supported, because invalid!
^/somepath(.*) otherpath$1 [P] not supported, because invalid!
---------------------------------------------- ----------------------------------
^/somepath(.*) /otherpath$1 /otherpath/pathinfo
^/somepath(.*) /otherpath$1 [R] http://thishost/otherpath/pathinfo
via external redirection
^/somepath(.*) /otherpath$1 [P] not supported, because silly!
---------------------------------------------- ----------------------------------
^/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] not supported, because silly!
---------------------------------------------- ----------------------------------
^/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
(i.e. file .htaccess in dir /physical/path/to/somepath containing
RewriteBase /somepath)
for
request ``GET /somepath/localpath/pathinfo'':
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] not supported, because silly!
---------------------------------------------- ----------------------------------
^localpath(.*) /otherpath$1 /otherpath/pathinfo
^localpath(.*) /otherpath$1 [R] http://thishost/otherpath/pathinfo
via external redirection
^localpath(.*) /otherpath$1 [P] not supported, because silly!
---------------------------------------------- ----------------------------------
^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] not supported, because silly!
---------------------------------------------- ----------------------------------
^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$1 [P] http://otherhost/otherpath/pathinfo
via internal proxy
We want to rewrite URLs of the form
into
/
Language
/~
Realname
/.../
File
/u/
Username
/.../
File
.
Language
/anywhere/map.real-to-user
. Then we only have to add the
following lines to the Apache server configuration file:
RewriteLog /anywhere/rewrite.log
RewriteMap real-to-user txt:/anywhere/map.real-to-host
RewriteRule ^/([^/]+)/~([^/]+)/(.*)$ /u/${real-to-user:$2|nobody}/$3.$1