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14 <p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p>
15 <p class="apache">Apache HTTP Server Version 2.5</p>
16 <img alt="" src="../images/feather.gif" /></div>
17 <div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
19 <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>
21 <p><span>Available Languages: </span><a href="../en/rewrite/rewritemap.html" title="English"> en </a></p>
25 <p>This document supplements the <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>
26 <a href="../mod/mod_rewrite.html">reference documentation</a>. It describes
27 the use of the <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> directive,
28 and provides examples of each of the various <code>RewriteMap</code> types.</p>
30 <div class="warning">Note that many of these examples won't work unchanged in your
31 particular server configuration, so it's important that you understand
32 them, rather than merely cutting and pasting the examples into your
36 <div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#introduction">Introduction</a></li>
37 <li><img alt="" src="../images/down.gif" /> <a href="#txt">txt: Plain text maps</a></li>
38 <li><img alt="" src="../images/down.gif" /> <a href="#rnd">rnd: Randomized Plain Text</a></li>
39 <li><img alt="" src="../images/down.gif" /> <a href="#dbm">dbm: DBM Hash File</a></li>
40 <li><img alt="" src="../images/down.gif" /> <a href="#int">int: Internal Function</a></li>
41 <li><img alt="" src="../images/down.gif" /> <a href="#prg">prg: External Rewriting Program</a></li>
42 <li><img alt="" src="../images/down.gif" /> <a href="#dbd">dbd or fastdbd: SQL Query</a></li>
43 <li><img alt="" src="../images/down.gif" /> <a href="#summary">Summary</a></li>
44 </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></ul></div>
45 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
47 <h2><a name="introduction" id="introduction">Introduction</a></h2>
51 The <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> directive
52 defines an external function which can be called in the context of
53 <code class="directive"><a href="../mod/mod_rewrite.html#rewriterule">RewriteRule</a></code> or
54 <code class="directive"><a href="../mod/mod_rewrite.html#rewritecond">RewriteCond</a></code> directives to
55 perform rewriting that is too complicated, or too specialized to be
56 performed just by regular expressions. The source of this lookup can
57 be any of the types listed in the sections below, and enumerated in
58 the <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> reference
61 <p>The syntax of the <code>RewriteMap</code> directive is as
64 <div class="example"><p><code>
65 RewriteMap <em>MapName</em> <em>MapType</em>:<em>MapSource</em>
68 <p>The <a id="mapfunc" name="mapfunc"><em>MapName</em></a> is an
69 arbitray name that you assign to the map, and which you will use in
70 directives later on. Arguments are passed to the map via the
75 <code>${</code> <em>MapName</em> <code>:</code> <em>LookupKey</em>
76 <code>}</code> <br /> <code>${</code> <em>MapName</em> <code>:</code>
77 <em>LookupKey</em> <code>|</code> <em>DefaultValue</em> <code>}</code>
81 <p>When such a construct occurs, the map <em>MapName</em> is
82 consulted and the key <em>LookupKey</em> is looked-up. If the
83 key is found, the map-function construct is substituted by
84 <em>SubstValue</em>. If the key is not found then it is
85 substituted by <em>DefaultValue</em> or by the empty string
86 if no <em>DefaultValue</em> was specified.</p>
88 <p>For example, you might define a
89 <code class="directive">RewriteMap</code> as:</p>
90 <div class="example"><p><code>
91 RewriteMap examplemap txt:/path/to/file/map.txt
93 <p>You would then be able to use this map in a
94 <code class="directive">RewriteRule</code> as follows:</p>
95 <div class="example"><p><code>
96 RewriteRule ^/ex/(.*) ${examplemap:$1}
99 <p>A default value can be specified in the event that nothing is found
102 <div class="example"><p><code>
103 RewriteRule ^/ex/(.*) ${examplemap:$1|/not_found.html}
106 <div class="note"><h3>Per-directory and .htaccess context</h3>
108 The <code>RewriteMap</code> directive may not be used in
109 <Directory> sections or <code>.htaccess</code> files. You must
110 declare the map in server or virtualhost context. You may use the map,
111 once created, in your <code>RewriteRule</code> and
112 <code>RewriteCond</code> directives in those scopes. You just can't
113 <strong>declare</strong> it in those scopes.
117 <p>The sections that follow describe the various <em>MapType</em>s that
118 may be used, and give examples of each.</p>
119 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
120 <div class="section">
121 <h2><a name="txt" id="txt">txt: Plain text maps</a></h2>
124 <p>When a MapType of <code>txt</code> is used, the MapSource is a filesystem path to a
125 plain-text mapping file, containing space-separated key/value pair
126 per line. Optionally, a line may be contain a comment, starting with
129 <p>For example, the following might be valid entries in a map
134 <strong><em>MatchingKey</em> <em>SubstValue</em></strong><br />
135 <strong><em>MatchingKey</em> <em>SubstValue</em></strong> # comment<br />
138 <p>When the RewriteMap is invoked the argument is looked for in the
139 first argument of a line, and, if found, the substitution value is
142 <p>For example, we might use a mapfile to translate product names to
143 product IDs for easier-to-remember URLs, using the following
146 <div class="example"><h3>Product to ID configuration</h3><p><code>
147 RewriteMap product2id txt:/etc/apache2/productmap.txt<br />
148 RewriteRule ^/product/(.*) /prods.php?id=${product2id:$1|NOTFOUND} [PT]
151 <p>We assume here that the <code>prods.php</code> script knows what
152 to do when it received an argument of <code>id=NOTFOUND</code> when
153 a product is not found in the lookup map.</p>
155 <p>The file <code>/etc/apache2/productmap.txt</code> then contains
158 <div class="example"><h3>Product to ID map</h3><p><code>
160 ## productmap.txt - Product to ID map file<br />
170 <p>Thus, when <code>http://example.com/product/television</code> is
171 requested, the <code>RewriteRule</code> is applied, and the request
172 is internally mapped to <code>/prods.php?id=993</code>.</p>
174 <div class="note"><h3>Note: .htaccess files</h3>
175 The example given is crafted to be used in server or virtualhost
176 scope. If you're planning to use this in a <code>.htaccess</code>
177 file, you'll need to remove the leading slash from the rewrite
178 pattern in order for it to match anything:
179 <div class="example"><p><code>
180 RewriteRule ^product/(.*) /prods.php?id=${product2id:$1|NOTFOUND} [PT]
184 <div class="note"><h3>Cached lookups</h3>
186 The looked-up keys are cached by httpd until the <code>mtime</code>
187 (modified time) of the mapfile changes, or the httpd server is
188 restarted. This ensures better performance on maps that are called
193 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
194 <div class="section">
195 <h2><a name="rnd" id="rnd">rnd: Randomized Plain Text</a></h2>
198 <p>When a MapType of <code>rnd</code> is used, the MapSource is a
199 filesystem path to a plain-text mapping file, each line of which
200 contains a key, and one or more values separated by <code>|</code>.
201 One of these values will be chosen at random if the key is
204 <p>For example, you might use the following map
205 file and directives to provide a random load balancing between
206 several back-end servers, via a reverse-proxy. Images are sent
207 to one of the servers in the 'static' pool, while everything
208 else is sent to one of the 'dynamic' pool.</p>
210 <div class="example"><h3>Rewrite map file</h3><p><code>
212 ## map.txt -- rewriting map<br />
215 static www1|www2|www3|www4<br />
219 <div class="example"><h3>Configuration directives</h3><p><code>
220 RewriteMap servers rnd:/path/to/file/map.txt<br />
222 RewriteRule ^/(.*\.(png|gif|jpg)) http://${servers:static}/$1 [NC,P,L]<br />
223 RewriteRule ^/(.*) http://${servers:dynamic}/$1 [P,L]
226 <p>So, when an image is requested and the first of these rules is
227 matched, <code>RewriteMap</code> looks up the string
228 <code>static</code> in the map file, which returns one of the
229 specified hostnames at random, which is then used in the
230 <code>RewriteRule</code> target.</p>
232 <p>If you wanted to have one of the servers more likely to be chosen
233 (for example, if one of the server has more memory than the others,
234 and so can handle more requests) simply list it more times in the
237 <div class="example"><p><code>
238 static www1|www1|www2|www3|www4
241 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
242 <div class="section">
243 <h2><a name="dbm" id="dbm">dbm: DBM Hash File</a></h2>
246 <p>When a MapType of <code>dbm</code> is used, the MapSource is a
247 filesystem path to a DBM database file containing key/value pairs to
248 be used in the mapping. This works exactly the same way as the
249 <code>txt</code> map, but is much faster, because a DBM is indexed,
250 whereas a text file is not. This allows more rapid access to the
253 <p>You may optionally specify a particular dbm type:</p>
255 <div class="example"><p><code>
256 RewriteMap examplemap dbm=sdbm:/etc/apache/mapfile.dbm
259 <p>The type can be sdbm, gdbm, ndbm or db.
260 However, it is recommended that you just use the <a href="../programs/httxt2dbm.html">httxt2dbm</a> utility that is
261 provided with Apache HTTP Server, as it will use the correct DBM library,
262 matching the one that was used when httpd itself was built.</p>
264 <p>To create a dbm file, first create a text map file as described
265 in the <a href="#txt">txt</a> section. Then run
266 <code>httxt2dbm</code>:</p>
268 <div class="example"><p><code>
269 $ httxt2dbm -i mapfile.txt -o mapfile.map
272 <p>You can then reference the resulting file in your
273 <code>RewriteMap</code> directive:</p>
275 <div class="example"><p><code>
276 RewriteMap mapname dbm:/etc/apache/mapfile.map
280 <p>Note that with some dbm types, more than one file is generated, with
281 a common base name. For example, you may have two files named
282 <code>mapfile.map.dir</code> and <code>mapfiile.map.pag</code>. This is
283 normal, and you need only use the base name <code>mapfile.map</code> in
284 your <code>RewriteMap</code> directive.</p>
287 <div class="note"><h3>Cached lookups</h3>
289 The looked-up keys are cached by httpd until the <code>mtime</code>
290 (modified time) of the mapfile changes, or the httpd server is
291 restarted. This ensures better performance on maps that are called
296 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
297 <div class="section">
298 <h2><a name="int" id="int">int: Internal Function</a></h2>
301 <p>When a MapType of <code>int</code> is used, the MapSource is one
302 of the available internal RewriteMap functions. Module authors can provide
303 additional internal functions by registering them with the
304 <code>ap_register_rewrite_mapfunc</code> API.
305 The functions that are provided by default are:
309 <li><strong>toupper</strong>:<br />
310 Converts the key to all upper case.</li>
311 <li><strong>tolower</strong>:<br />
312 Converts the key to all lower case.</li>
313 <li><strong>escape</strong>:<br />
314 Translates special characters in the key to
316 <li><strong>unescape</strong>:<br />
317 Translates hex-encodings in the key back to
318 special characters.</li>
322 To use one of these functions, create a <code>RewriteMap</code> referencing
323 the int function, and then use that in your <code>RewriteRule</code>:
326 <div class="example"><h3>Redirect a URI to an all-lowercase version of itself</h3><p><code>
327 RewriteMap lc int:tolower<br />
328 RewriteRule (.*?[A-Z]+.*) ${lc:$1} [R]
332 <p>Please note that the example offered here is for
333 illustration purposes only, and is not a recommendation. If you want
334 to make URLs case-insensitive, consider using
335 <code class="module"><a href="../mod/mod_speling.html">mod_speling</a></code> instead.
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>This feature utilizes the <code>rewrite-map</code> mutex,
362 which is required for reliable communication with the program.
363 The mutex mechanism and lock file can be configured with the
364 <code class="directive"><a href="../mod/core.html#mutex">Mutex</a></code> directive.</p>
366 <p>A simple example is shown here which will replace all dashes with
367 underscores in a request URI.</p>
369 <div class="example"><h3>Rewrite configuration</h3><p><code>
370 RewriteMap d2u prg:/www/bin/dash2under.pl<br />
371 RewriteRule - ${d2u:%{REQUEST_URI}}
374 <div class="example"><h3>dash2under.pl</h3><p><code>
375 #!/usr/bin/perl<br />
376 $| = 1; # Turn off I/O buffering<br />
377 while (<STDIN>) {<br />
378 <span class="indent">
379 s/-/_/g; # Replace dashes with underscores<br />
385 <div class="note"><h3>Caution!</h3>
387 <li>Keep your rewrite map program as simple as possible. If the program
388 hangs, it will cause httpd to wait indefinitely for a response from the
389 map, which will, in turn, cause httpd to stop responding to
391 <li>Be sure to turn off buffering in your program. In Perl this is done
392 by the second line in the example script: <code>$| = 1;</code> This will
393 of course vary in other languages. Buffered I/O will cause httpd to wait
394 for the output, and so it will hang.</li>
395 <li>Remember that there is only one copy of the program, started at
396 server startup. All requests will need to go through this one bottleneck.
397 This can cause significant slowdowns if many requests must go through
398 this process, or if the script itself is very slow.</li>
402 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
403 <div class="section">
404 <h2><a name="dbd" id="dbd">dbd or fastdbd: SQL Query</a></h2>
407 <p>When a MapType of <code>dbd</code> or <code>fastdbd</code> is
408 used, the MapSource is a SQL SELECT statement that takes a single
409 argument and returns a single value.</p>
411 <p><code class="module"><a href="../mod/mod_dbd.html">mod_dbd</a></code> will need to be configured to point at
412 the right database for this statement to be executed.</p>
414 <p>There are two forms of this MapType.
415 Using a MapType of <code>dbd</code> causes the query to be
416 executed with each map request, while using <code>fastdbd</code>
417 caches the database lookups internally. So, while
418 <code>fastdbd</code> is more efficient, and therefore faster, it
419 won't pick up on changes to the database until the server is
422 <p>If a query returns more than one row, a random row from
423 the result set is used.</p>
425 <div class="example"><h3>Example</h3><p><code>
426 RewriteMap myquery "fastdbd:SELECT destination FROM rewrite WHERE source = %s"
429 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
430 <div class="section">
431 <h2><a name="summary" id="summary">Summary</a></h2>
434 <p>The <code class="directive">RewriteMap</code> directive can occur more than
435 once. For each mapping-function use one
436 <code class="directive">RewriteMap</code> directive to declare its rewriting
439 <p>While you cannot <strong>declare</strong> a map in
440 per-directory context (<code>.htaccess</code> files or
441 <Directory> blocks) it is possible to
442 <strong>use</strong> this map in per-directory context. </p>
445 <div class="bottomlang">
446 <p><span>Available Languages: </span><a href="../en/rewrite/rewritemap.html" title="English"> en </a></p>
447 </div><div id="footer">
448 <p class="apache">Copyright 2012 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
449 <p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p></div>