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20 <p class="apache">Apache HTTP Server Version 2.5</p>
21 <img alt="" src="../images/feather.png" /></div>
22 <div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
24 <a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.5</a> > <a href="./">Rewrite</a></div><div id="page-content"><div id="preamble"><h1>Using RewriteMap</h1>
26 <p><span>Available Languages: </span><a href="../en/rewrite/rewritemap.html" title="English"> en </a></p>
30 <p>This document supplements the <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>
31 <a href="../mod/mod_rewrite.html">reference documentation</a>. It describes
32 the use of the <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> directive,
33 and provides examples of each of the various <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> types.</p>
35 <div class="warning">Note that many of these examples won't work unchanged in your
36 particular server configuration, so it's important that you understand
37 them, rather than merely cutting and pasting the examples into your
41 <div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#introduction">Introduction</a></li>
42 <li><img alt="" src="../images/down.gif" /> <a href="#int">int: Internal Function</a></li>
43 <li><img alt="" src="../images/down.gif" /> <a href="#txt">txt: Plain text maps</a></li>
44 <li><img alt="" src="../images/down.gif" /> <a href="#rnd">rnd: Randomized Plain Text</a></li>
45 <li><img alt="" src="../images/down.gif" /> <a href="#dbm">dbm: DBM Hash File</a></li>
46 <li><img alt="" src="../images/down.gif" /> <a href="#prg">prg: External Rewriting Program</a></li>
47 <li><img alt="" src="../images/down.gif" /> <a href="#dbd">dbd or fastdbd: SQL Query</a></li>
48 <li><img alt="" src="../images/down.gif" /> <a href="#summary">Summary</a></li>
49 </ul><h3>See also</h3><ul class="seealso"><li><a href="../mod/mod_rewrite.html">Module documentation</a></li><li><a href="intro.html">mod_rewrite introduction</a></li><li><a href="remapping.html">Redirection and remapping</a></li><li><a href="access.html">Controlling access</a></li><li><a href="vhosts.html">Virtual hosts</a></li><li><a href="proxy.html">Proxying</a></li><li><a href="advanced.html">Advanced techniques</a></li><li><a href="avoid.html">When not to use mod_rewrite</a></li><li><a href="#comments_section">Comments</a></li></ul></div>
50 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
52 <h2><a name="introduction" id="introduction">Introduction</a></h2>
56 The <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> directive
57 defines an external function which can be called in the context of
58 <code class="directive"><a href="../mod/mod_rewrite.html#rewriterule">RewriteRule</a></code> or
59 <code class="directive"><a href="../mod/mod_rewrite.html#rewritecond">RewriteCond</a></code> directives to
60 perform rewriting that is too complicated, or too specialized to be
61 performed just by regular expressions. The source of this lookup can
62 be any of the types listed in the sections below, and enumerated in
63 the <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> reference
66 <p>The syntax of the <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code>
67 directive is as follows:</p>
69 <pre class="prettyprint lang-config">RewriteMap <em>MapName</em> <em>MapType</em>:<em>MapSource</em>
73 <p>The <a id="mapfunc" name="mapfunc"><em>MapName</em></a> is an
74 arbitray name that you assign to the map, and which you will use in
75 directives later on. Arguments are passed to the map via the
80 <code>${</code> <em>MapName</em> <code>:</code> <em>LookupKey</em>
81 <code>}</code> <br /> <code>${</code> <em>MapName</em> <code>:</code>
82 <em>LookupKey</em> <code>|</code> <em>DefaultValue</em> <code>}</code>
86 <p>When such a construct occurs, the map <em>MapName</em> is
87 consulted and the key <em>LookupKey</em> is looked-up. If the
88 key is found, the map-function construct is substituted by
89 <em>SubstValue</em>. If the key is not found then it is
90 substituted by <em>DefaultValue</em> or by the empty string
91 if no <em>DefaultValue</em> was specified.</p>
93 <p>For example, you can define a
94 <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> as:</p>
95 <pre class="prettyprint lang-config">RewriteMap examplemap "txt:/path/to/file/map.txt"</pre>
97 <p>You would then be able to use this map in a
98 <code class="directive"><a href="../mod/mod_rewrite.html#rewriterule">RewriteRule</a></code> as follows:</p>
99 <pre class="prettyprint lang-config">RewriteRule "^/ex/(.*)" "${examplemap:$1}"</pre>
102 <p>A default value can be specified in the event that nothing is found
105 <pre class="prettyprint lang-config">RewriteRule "^/ex/(.*)" "${examplemap:$1|/not_found.html}"</pre>
108 <div class="note"><h3>Per-directory and .htaccess context</h3>
110 The <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> directive may not be
111 used in <code class="directive"><a href="../mod/core.html#directory"><Directory></a></code> sections or
112 <code>.htaccess</code> files. You must
113 declare the map in server or virtualhost context. You may use the map,
114 once created, in your <code class="directive"><a href="../mod/mod_rewrite.html#rewriterule">RewriteRule</a></code> and
115 <code class="directive"><a href="../mod/mod_rewrite.html#rewritecond">RewriteCond</a></code> directives in those
116 scopes. You just can't <strong>declare</strong> it in those scopes.</p>
119 <p>The sections that follow describe the various <em>MapType</em>s that
120 may be used, and give examples of each.</p>
121 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
122 <div class="section">
123 <h2><a name="int" id="int">int: Internal Function</a></h2>
126 <p>When a MapType of <code>int</code> is used, the MapSource is one
127 of the available internal <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code>
128 functions. Module authors can provide
129 additional internal functions by registering them with the
130 <code>ap_register_rewrite_mapfunc</code> API.
131 The functions that are provided by default are:
135 <li><strong>toupper</strong>:<br />
136 Converts the key to all upper case.</li>
137 <li><strong>tolower</strong>:<br />
138 Converts the key to all lower case.</li>
139 <li><strong>escape</strong>:<br />
140 Translates special characters in the key to
142 <li><strong>unescape</strong>:<br />
143 Translates hex-encodings in the key back to
144 special characters.</li>
148 To use one of these functions, create a <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> referencing
149 the int function, and then use that in your <code class="directive"><a href="../mod/mod_rewrite.html#rewriterule">RewriteRule</a></code>:
152 <p> <strong>Redirect a URI to an all-lowercase version of itself</strong></p>
153 <pre class="prettyprint lang-config">RewriteMap lc int:tolower
154 RewriteRule "(.*)" "${lc:$1}" [R]</pre>
158 <p>Please note that the example offered here is for
159 illustration purposes only, and is not a recommendation. If you want
160 to make URLs case-insensitive, consider using
161 <code class="module"><a href="../mod/mod_speling.html">mod_speling</a></code> instead.
165 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
166 <div class="section">
167 <h2><a name="txt" id="txt">txt: Plain text maps</a></h2>
170 <p>When a MapType of <code>txt</code> is used, the MapSource is a filesystem path to a
171 plain-text mapping file, containing one space-separated key/value pair
172 per line. Optionally, a line may contain a comment, starting with
175 <p>A valid text rewrite map file will have the following syntax:</p>
177 <div class="example"><p><code>
179 <strong><em>MatchingKey</em> <em>SubstValue</em></strong><br />
180 <strong><em>MatchingKey</em> <em>SubstValue</em></strong> # comment<br />
183 <p>When the <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> is invoked
184 the argument is looked for in the
185 first argument of a line, and, if found, the substitution value is
188 <p>For example, we can use a mapfile to translate product names to
189 product IDs for easier-to-remember URLs, using the following
191 <p><strong>Product to ID configuration</strong></p>
192 <pre class="prettyprint lang-config">RewriteMap product2id "txt:/etc/apache2/productmap.txt"
193 RewriteRule "^/product/(.*)" "/prods.php?id=${product2id:$1|NOTFOUND}" [PT]</pre>
196 <p>We assume here that the <code>prods.php</code> script knows what
197 to do when it received an argument of <code>id=NOTFOUND</code> when
198 a product is not found in the lookup map.</p>
200 <p>The file <code>/etc/apache2/productmap.txt</code> then contains
203 <div class="example"><h3>Product to ID map</h3><p><code>
205 ## productmap.txt - Product to ID map file<br />
215 <p>Thus, when <code>http://example.com/product/television</code> is
216 requested, the <code class="directive"><a href="../mod/mod_rewrite.html#rewriterule">RewriteRule</a></code> is
217 applied, and the request
218 is internally mapped to <code>/prods.php?id=993</code>.</p>
220 <div class="note"><h3>Note: .htaccess files</h3>
221 The example given is crafted to be used in server or virtualhost
222 scope. If you're planning to use this in a <code>.htaccess</code>
223 file, you'll need to remove the leading slash from the rewrite
224 pattern in order for it to match anything:
225 <pre class="prettyprint lang-config">RewriteRule "^product/(.*)" "/prods.php?id=${product2id:$1|NOTFOUND}" [PT]</pre>
229 <div class="note"><h3>Cached lookups</h3>
231 The looked-up keys are cached by httpd until the <code>mtime</code>
232 (modified time) of the mapfile changes, or the httpd server is
233 restarted. This ensures better performance on maps that are called
238 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
239 <div class="section">
240 <h2><a name="rnd" id="rnd">rnd: Randomized Plain Text</a></h2>
243 <p>When a MapType of <code>rnd</code> is used, the MapSource is a
244 filesystem path to a plain-text mapping file, each line of which
245 contains a key, and one or more values separated by <code>|</code>.
246 One of these values will be chosen at random if the key is
249 <p>For example, you can use the following map
250 file and directives to provide a random load balancing between
251 several back-end servers, via a reverse-proxy. Images are sent
252 to one of the servers in the 'static' pool, while everything
253 else is sent to one of the 'dynamic' pool.</p>
255 <div class="example"><h3>Rewrite map file</h3><p><code>
257 ## map.txt -- rewriting map<br />
260 static www1|www2|www3|www4<br />
263 <p><strong>Configuration directives</strong></p>
264 <pre class="prettyprint lang-config">RewriteMap servers "rnd:/path/to/file/map.txt"
266 RewriteRule "^/(.*\.(png|gif|jpg))" "http://${servers:static}/$1" [NC,P,L]
267 RewriteRule "^/(.*)" "http://${servers:dynamic}/$1" [P,L]</pre>
270 <p>So, when an image is requested and the first of these rules is
271 matched, <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> looks up the string
272 <code>static</code> in the map file, which returns one of the
273 specified hostnames at random, which is then used in the
274 <code class="directive"><a href="../mod/mod_rewrite.html#rewriterule">RewriteRule</a></code> target.</p>
276 <p>If you wanted to have one of the servers more likely to be chosen
277 (for example, if one of the server has more memory than the others,
278 and so can handle more requests) simply list it more times in the
281 <div class="example"><p><code>
282 static www1|www1|www2|www3|www4
285 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
286 <div class="section">
287 <h2><a name="dbm" id="dbm">dbm: DBM Hash File</a></h2>
290 <p>When a MapType of <code>dbm</code> is used, the MapSource is a
291 filesystem path to a DBM database file containing key/value pairs to
292 be used in the mapping. This works exactly the same way as the
293 <code>txt</code> map, but is much faster, because a DBM is indexed,
294 whereas a text file is not. This allows more rapid access to the
297 <p>You may optionally specify a particular dbm type:</p>
299 <pre class="prettyprint lang-config">RewriteMap examplemap "dbm=sdbm:/etc/apache/mapfile.dbm"</pre>
302 <p>The type can be <code>sdbm</code>, <code>gdbm</code>, <code>ndbm</code>
304 However, it is recommended that you just use the <a href="../programs/httxt2dbm.html">httxt2dbm</a> utility that is
305 provided with Apache HTTP Server, as it will use the correct DBM library,
306 matching the one that was used when httpd itself was built.</p>
308 <p>To create a dbm file, first create a text map file as described
309 in the <a href="#txt">txt</a> section. Then run
310 <code>httxt2dbm</code>:</p>
312 <div class="example"><p><code>
313 $ httxt2dbm -i mapfile.txt -o mapfile.map
316 <p>You can then reference the resulting file in your
317 <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> directive:</p>
319 <pre class="prettyprint lang-config">RewriteMap mapname "dbm:/etc/apache/mapfile.map"</pre>
323 <p>Note that with some dbm types, more than one file is generated, with
324 a common base name. For example, you may have two files named
325 <code>mapfile.map.dir</code> and <code>mapfiile.map.pag</code>. This is
326 normal, and you need only use the base name <code>mapfile.map</code> in
327 your <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> directive.</p>
330 <div class="note"><h3>Cached lookups</h3>
332 The looked-up keys are cached by httpd until the <code>mtime</code>
333 (modified time) of the mapfile changes, or the httpd server is
334 restarted. This ensures better performance on maps that are called
339 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
340 <div class="section">
341 <h2><a name="prg" id="prg">prg: External Rewriting Program</a></h2>
343 <p>When a MapType of <code>prg</code> is used, the MapSource is a
344 filesystem path to an executable program which will providing the
345 mapping behavior. This can be a compiled binary file, or a program
346 in an interpreted language such as Perl or Python.</p>
348 <p>This program is started once, when the Apache HTTP Server is
349 started, and then communicates with the rewriting engine via
350 <code>STDIN</code> and <code>STDOUT</code>. That is, for each map
351 function lookup, it expects one argument via <code>STDIN</code>, and
352 should return one new-line terminated response string on
353 <code>STDOUT</code>. If there is no corresponding lookup value, the
354 map program should return the four-character string
355 "<code>NULL</code>" to indicate this.</p>
357 <p>External rewriting programs are not started if they're defined in
358 a context that does not have <code class="directive"><a href="../mod/mod_rewrite.html#rewriteengine">RewriteEngine</a></code> set to
361 <p>By default, external rewriting programs are run as the
362 user:group who started httpd. This can be changed on UNIX systems
363 by passing user name and group name as third argument to
364 <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> in the
365 <code>username:groupname</code> format.</p>
367 <p>This feature utilizes the <code>rewrite-map</code> mutex,
368 which is required for reliable communication with the program.
369 The mutex mechanism and lock file can be configured with the
370 <code class="directive"><a href="../mod/core.html#mutex">Mutex</a></code> directive.</p>
372 <p>A simple example is shown here which will replace all dashes with
373 underscores in a request URI.</p>
375 <p><strong>Rewrite configuration</strong></p>
376 <pre class="prettyprint lang-config">RewriteMap d2u "prg:/www/bin/dash2under.programlisting" apache:apache
377 RewriteRule "-" "${d2u:%{REQUEST_URI}}"</pre>
380 <p><strong>dash2under.pl</strong></p>
381 <pre class="prettyprint lang-perl">#!/usr/bin/perl
382 $| = 1; # Turn off I/O buffering
383 while (<STDIN>) {
384 s/-/_/g; # Replace dashes with underscores
389 <div class="note"><h3>Caution!</h3>
391 <li>Keep your rewrite map program as simple as possible. If the program
392 hangs, it will cause httpd to wait indefinitely for a response from the
393 map, which will, in turn, cause httpd to stop responding to
395 <li>Be sure to turn off buffering in your program. In Perl this is done
396 by the second line in the example script: <code>$| = 1;</code> This will
397 of course vary in other languages. Buffered I/O will cause httpd to wait
398 for the output, and so it will hang.</li>
399 <li>Remember that there is only one copy of the program, started at
400 server startup. All requests will need to go through this one bottleneck.
401 This can cause significant slowdowns if many requests must go through
402 this process, or if the script itself is very slow.</li>
406 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
407 <div class="section">
408 <h2><a name="dbd" id="dbd">dbd or fastdbd: SQL Query</a></h2>
411 <p>When a MapType of <code>dbd</code> or <code>fastdbd</code> is
412 used, the MapSource is a SQL SELECT statement that takes a single
413 argument and returns a single value.</p>
415 <p><code class="module"><a href="../mod/mod_dbd.html">mod_dbd</a></code> will need to be configured to point at
416 the right database for this statement to be executed.</p>
418 <p>There are two forms of this MapType.
419 Using a MapType of <code>dbd</code> causes the query to be
420 executed with each map request, while using <code>fastdbd</code>
421 caches the database lookups internally. So, while
422 <code>fastdbd</code> is more efficient, and therefore faster, it
423 won't pick up on changes to the database until the server is
426 <p>If a query returns more than one row, a random row from
427 the result set is used.</p>
429 <div class="example"><h3>Example</h3><pre class="prettyprint lang-config">RewriteMap myquery "fastdbd:SELECT destination FROM rewrite WHERE source = %s"</pre>
432 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
433 <div class="section">
434 <h2><a name="summary" id="summary">Summary</a></h2>
437 <p>The <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> directive can
438 occur more than once. For each mapping-function use one
439 <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> directive to declare
440 its rewriting mapfile.</p>
442 <p>While you cannot <strong>declare</strong> a map in
443 per-directory context (<code>.htaccess</code> files or
444 <code class="directive"><a href="../mod/core.html#directory"><Directory></a></code> blocks) it is
445 possible to <strong>use</strong> this map in per-directory context.</p>
448 <div class="bottomlang">
449 <p><span>Available Languages: </span><a href="../en/rewrite/rewritemap.html" title="English"> en </a></p>
450 </div><div class="top"><a href="#page-header"><img src="../images/up.gif" alt="top" /></a></div><div class="section"><h2><a id="comments_section" name="comments_section">Comments</a></h2><div class="warning"><strong>Notice:</strong><br />This is not a Q&A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed again by our moderators if they are either implemented or considered invalid/off-topic. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Freenode, or sent to our <a href="http://httpd.apache.org/lists.html">mailing lists</a>.</div>
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