apache/docs/manual/rewrite/rewrite_guide.html.en

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   8 <title>URL Rewriting Guide - Apache HTTP Server</title>
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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 2.3</p>
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  17 <div class="up"><a href="./"><img title="&lt;-" alt="&lt;-" src="../images/left.gif" /></a></div>
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  19 <a href="http://www.apache.org/">Apache</a> &gt; <a href="http://httpd.apache.org/">HTTP Server</a> &gt; <a href="http://httpd.apache.org/docs/">Documentation</a> &gt; <a href="../">Version 2.3</a> &gt; <a href="./">Rewrite</a></div><div id="page-content"><div id="preamble"><h1>URL Rewriting Guide</h1>
  20 <div class="toplang">
  21 <p><span>Available Languages: </span><a href="../en/rewrite/rewrite_guide.html" title="English">&nbsp;en&nbsp;</a></p>
  22 </div>
  23
  24
  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>.
  27     It describes how one can use Apache's <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>
  28     to solve typical URL-based problems with which webmasters are
  29     commonly confronted. We give detailed descriptions on how to
  30     solve each problem by configuring URL rewriting rulesets.</p>
  31
  32     <div class="warning">ATTENTION: Depending on your server configuration
  33     it may be necessary to slightly change the examples for your
  34     situation, e.g. adding the <code>[PT]</code> flag when
  35     additionally using <code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code> and
  36     <code class="module"><a href="../mod/mod_userdir.html">mod_userdir</a></code>, etc. Or rewriting a ruleset
  37     to fit in <code>.htaccess</code> context instead
  38     of per-server context. Always try to understand what a
  39     particular ruleset really does before you use it. This
  40     avoids many problems.</div>
  41
  42   </div>
  43 <div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#canonicalurl">Canonical URLs</a></li>
  44 <li><img alt="" src="../images/down.gif" /> <a href="#canonicalhost">Canonical Hostnames</a></li>
  45 <li><img alt="" src="../images/down.gif" /> <a href="#moveddocroot">Moved <code>DocumentRoot</code></a></li>
  46 <li><img alt="" src="../images/down.gif" /> <a href="#trailingslash">Trailing Slash Problem</a></li>
  47 <li><img alt="" src="../images/down.gif" /> <a href="#movehomedirs">Move Homedirs to Different Webserver</a></li>
  48 <li><img alt="" src="../images/down.gif" /> <a href="#multipledirs">Search for pages in more than one directory</a></li>
  49 <li><img alt="" src="../images/down.gif" /> <a href="#setenvvars">Set Environment Variables According To URL Parts</a></li>
  50 <li><img alt="" src="../images/down.gif" /> <a href="#uservhosts">Virtual Hosts Per User</a></li>
  51 <li><img alt="" src="../images/down.gif" /> <a href="#redirecthome">Redirect Homedirs For Foreigners</a></li>
  52 <li><img alt="" src="../images/down.gif" /> <a href="#redirectanchors">Redirecting Anchors</a></li>
  53 <li><img alt="" src="../images/down.gif" /> <a href="#time-dependent">Time-Dependent Rewriting</a></li>
  54 <li><img alt="" src="../images/down.gif" /> <a href="#backward-compatibility">Backward Compatibility for YYYY to XXXX migration</a></li>
  55 <li><img alt="" src="../images/down.gif" /> <a href="#old-to-new">From Old to New (intern)</a></li>
  56 <li><img alt="" src="../images/down.gif" /> <a href="#old-to-new-extern">From Old to New (extern)</a></li>
  57 <li><img alt="" src="../images/down.gif" /> <a href="#static-to-dynamic">From Static to Dynamic</a></li>
  58 <li><img alt="" src="../images/down.gif" /> <a href="#blocking-of-robots">Blocking of Robots</a></li>
  59 <li><img alt="" src="../images/down.gif" /> <a href="#blocked-inline-images">Forbidding Image "Hotlinking"</a></li>
  60 <li><img alt="" src="../images/down.gif" /> <a href="#proxy-deny">Proxy Deny</a></li>
  61 <li><img alt="" src="../images/down.gif" /> <a href="#external-rewriting">External Rewriting Engine</a></li>
  62 </ul><h3>See also</h3><ul class="seealso"><li><a href="../mod/mod_rewrite.html">Module
  63 documentation</a></li><li><a href="rewrite_intro.html">mod_rewrite
  64 introduction</a></li><li><a href="rewrite_guide_advanced.html">Advanced Rewrite Guide - advanced
  65 useful examples</a></li><li><a href="rewrite_tech.html">Technical details</a></li></ul></div>
  66 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
  67 <div class="section">
  68 <h2><a name="canonicalurl" id="canonicalurl">Canonical URLs</a></h2>
  69
  70
  71
  72 <dl>
  73  <dt>Description:</dt>
  74
  75    <dd>
  76      <p>On some webservers there are more than one URL for a
  77      resource. Usually there are canonical URLs (which should be
  78      actually used and distributed) and those which are just
  79      shortcuts, internal ones, etc. Independent of which URL the
  80      user supplied with the request he should finally see the
  81      canonical one only.</p>
  82    </dd>
  83
  84    <dt>Solution:</dt>
  85
  86      <dd>
  87        <p>We do an external HTTP redirect for all non-canonical
  88        URLs to fix them in the location view of the Browser and
  89        for all subsequent requests. In the example ruleset below
  90        we replace <code>/~user</code> by the canonical
  91        <code>/u/user</code> and fix a missing trailing slash for
  92        <code>/u/user</code>.</p>
  93
  94 <div class="example"><pre>
  95 RewriteRule   ^/<strong>~</strong>([^/]+)/?(.*)    /<strong>u</strong>/$1/$2  [<strong>R</strong>]
  96 RewriteRule   ^/u/(<strong>[^/]+</strong>)$  /$1/$2<strong>/</strong>   [<strong>R</strong>]
  97 </pre></div>
  98         </dd>
  99       </dl>
 100
 101     </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 102 <div class="section">
 103 <h2><a name="canonicalhost" id="canonicalhost">Canonical Hostnames</a></h2>
 104
 105       <dl>
 106         <dt>Description:</dt>
 107
 108         <dd>The goal of this rule is to force the use of a particular
 109         hostname, in preference to other hostnames which may be used to
 110         reach the same site. For example, if you wish to force the use
 111         of <strong>www.example.com</strong> instead of
 112         <strong>example.com</strong>, you might use a variant of the
 113         following recipe.</dd>
 114
 115         <dt>Solution:</dt>
 116
 117         <dd>
 118 <p>For sites running on a port other than 80:</p>
 119 <div class="example"><pre>
 120 RewriteCond %{HTTP_HOST}   !^www\.example\.com [NC]
 121 RewriteCond %{HTTP_HOST}   !^$
 122 RewriteCond %{SERVER_PORT} !^80$
 123 RewriteRule ^/?(.*)         http://www.example.com:%{SERVER_PORT}/$1 [L,R]
 124 </pre></div>
 125
 126 <p>And for a site running on port 80</p>
 127 <div class="example"><pre>
 128 RewriteCond %{HTTP_HOST}   !^www\.example\.com [NC]
 129 RewriteCond %{HTTP_HOST}   !^$
 130 RewriteRule ^/?(.*)         http://www.example.com/$1 [L,R]
 131 </pre></div>
 132
 133         <p>
 134         If you wanted to do this generically for all domain names - that
 135         is, if you want to redirect <strong>example.com</strong> to
 136         <strong>www.example.com</strong> for all possible values of
 137         <strong>example.com</strong>, you could use the following
 138         recipe:</p>
 139
 140 <div class="example"><pre>
 141 RewriteCond %{HTTP_HOST} !^www\. [NC]
 142 RewriteCond %{HTTP_HOST} !^$
 143 RewriteRule ^/?(.*) http://www.%{HTTP_HOST}/$1 [L,R]
 144 </pre></div>
 145
 146     <p>These rulesets will work either in your main server configuration
 147     file, or in a <code>.htaccess</code> file placed in the <code class="directive"><a href="../mod/core.html#documentroot">DocumentRoot</a></code> of the server.</p>
 148         </dd>
 149       </dl>
 150
 151     </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 152 <div class="section">
 153 <h2><a name="moveddocroot" id="moveddocroot">Moved <code>DocumentRoot</code></a></h2>
 154
 155
 156
 157       <dl>
 158         <dt>Description:</dt>
 159
 160         <dd>
 161 <p>Usually the <code class="directive"><a href="../mod/core.html#documentroot">DocumentRoot</a></code>
 162 of the webserver directly relates to the URL "<code>/</code>".
 163 But often this data is not really of top-level priority. For example,
 164 you may wish for visitors, on first entering a site, to go to a
 165 particular subdirectory <code>/about/</code>. This may be accomplished
 166 using the following ruleset:</p>
 167 </dd>
 168
 169         <dt>Solution:</dt>
 170
 171         <dd>
 172           <p>We redirect the URL <code>/</code> to
 173           <code>/about/</code>:
 174           </p>
 175
 176 <div class="example"><pre>
 177 RewriteEngine on
 178 RewriteRule   <strong>^/$</strong>  /about/  [<strong>R</strong>]
 179 </pre></div>
 180
 181     <p>Note that this can also be handled using the <code class="directive"><a href="../mod/mod_alias.html#redirectmatch">RedirectMatch</a></code> directive:</p>
 182
 183 <div class="example"><p><code>
 184 RedirectMatch ^/$ http://example.com/about/
 185 </code></p></div>
 186
 187 <p>Note also that the example rewrites only the root URL. That is, it
 188 rewrites a request for <code>http://example.com/</code>, but not a
 189 request for <code>http://example.com/page.html</code>. If you have in
 190 fact changed your document root - that is, if <strong>all</strong> of
 191 your content is in fact in that subdirectory, it is greatly preferable
 192 to simply change your <code class="directive"><a href="../mod/core.html#documentroot">DocumentRoot</a></code>
 193 directive, rather than rewriting URLs.</p>
 194 </dd>
 195 </dl>
 196
 197     </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 198 <div class="section">
 199 <h2><a name="trailingslash" id="trailingslash">Trailing Slash Problem</a></h2>
 200
 201
 202
 203       <dl>
 204         <dt>Description:</dt>
 205
 206     <dd><p>The vast majority of "trailing slash" problems can be dealt
 207     with using the techniques discussed in the <a href="http://httpd.apache.org/docs/misc/FAQ-E.html#set-servername">FAQ
 208     entry</a>. However, occasionally, there is a need to use mod_rewrite
 209     to handle a case where a missing trailing slash causes a URL to
 210     fail. This can happen, for example, after a series of complex
 211     rewrite rules.</p>
 212     </dd>
 213
 214         <dt>Solution:</dt>
 215
 216         <dd>
 217           <p>The solution to this subtle problem is to let the server
 218           add the trailing slash automatically. To do this
 219           correctly we have to use an external redirect, so the
 220           browser correctly requests subsequent images etc. If we
 221           only did a internal rewrite, this would only work for the
 222           directory page, but would go wrong when any images are
 223           included into this page with relative URLs, because the
 224           browser would request an in-lined object. For instance, a
 225           request for <code>image.gif</code> in
 226           <code>/~quux/foo/index.html</code> would become
 227           <code>/~quux/image.gif</code> without the external
 228           redirect!</p>
 229
 230           <p>So, to do this trick we write:</p>
 231
 232 <div class="example"><pre>
 233 RewriteEngine  on
 234 RewriteBase    /~quux/
 235 RewriteRule    ^foo<strong>$</strong>  foo<strong>/</strong>  [<strong>R</strong>]
 236 </pre></div>
 237
 238    <p>Alternately, you can put the following in a
 239    top-level <code>.htaccess</code> file in the content directory.
 240    But note that this creates some processing overhead.</p>
 241
 242 <div class="example"><pre>
 243 RewriteEngine  on
 244 RewriteBase    /~quux/
 245 RewriteCond    %{REQUEST_FILENAME}  <strong>-d</strong>
 246 RewriteRule    ^(.+<strong>[^/]</strong>)$           $1<strong>/</strong>  [R]
 247 </pre></div>
 248         </dd>
 249       </dl>
 250
 251     </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 252 <div class="section">
 253 <h2><a name="movehomedirs" id="movehomedirs">Move Homedirs to Different Webserver</a></h2>
 254
 255
 256
 257       <dl>
 258         <dt>Description:</dt>
 259
 260         <dd>
 261           <p>Many webmasters have asked for a solution to the
 262           following situation: They wanted to redirect just all
 263           homedirs on a webserver to another webserver. They usually
 264           need such things when establishing a newer webserver which
 265           will replace the old one over time.</p>
 266         </dd>
 267
 268         <dt>Solution:</dt>
 269
 270         <dd>
 271           <p>The solution is trivial with <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.
 272           On the old webserver we just redirect all
 273           <code>/~user/anypath</code> URLs to
 274           <code>http://newserver/~user/anypath</code>.</p>
 275
 276 <div class="example"><pre>
 277 RewriteEngine on
 278 RewriteRule   ^/~(.+)  http://<strong>newserver</strong>/~$1  [R,L]
 279 </pre></div>
 280         </dd>
 281       </dl>
 282
 283     </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 284 <div class="section">
 285 <h2><a name="multipledirs" id="multipledirs">Search for pages in more than one directory</a></h2>
 286
 287
 288
 289       <dl>
 290         <dt>Description:</dt>
 291
 292         <dd>
 293           <p>Sometimes it is necessary to let the webserver search
 294           for pages in more than one directory. Here MultiViews or
 295           other techniques cannot help.</p>
 296         </dd>
 297
 298         <dt>Solution:</dt>
 299
 300         <dd>
 301           <p>We program a explicit ruleset which searches for the
 302           files in the directories.</p>
 303
 304 <div class="example"><pre>
 305 RewriteEngine on
 306
 307 #   first try to find it in dir1/...
 308 #   ...and if found stop and be happy:
 309 RewriteCond         %{DOCUMENT_ROOT}/<strong>dir1</strong>/%{REQUEST_URI}  -f
 310 RewriteRule  ^(.+)  %{DOCUMENT_ROOT}/<strong>dir1</strong>/$1  [L]
 311
 312 #   second try to find it in dir2/...
 313 #   ...and if found stop and be happy:
 314 RewriteCond         %{DOCUMENT_ROOT}/<strong>dir2</strong>/%{REQUEST_URI}  -f
 315 RewriteRule  ^(.+)  %{DOCUMENT_ROOT}/<strong>dir2</strong>/$1  [L]
 316
 317 #   else go on for other Alias or ScriptAlias directives,
 318 #   etc.
 319 RewriteRule   ^(.+)  -  [PT]
 320 </pre></div>
 321         </dd>
 322       </dl>
 323
 324     </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 325 <div class="section">
 326 <h2><a name="setenvvars" id="setenvvars">Set Environment Variables According To URL Parts</a></h2>
 327
 328
 329
 330       <dl>
 331         <dt>Description:</dt>
 332
 333         <dd>
 334           <p>Perhaps you want to keep status information between
 335           requests and use the URL to encode it. But you don't want
 336           to use a CGI wrapper for all pages just to strip out this
 337           information.</p>
 338         </dd>
 339
 340         <dt>Solution:</dt>
 341
 342         <dd>
 343           <p>We use a rewrite rule to strip out the status information
 344           and remember it via an environment variable which can be
 345           later dereferenced from within XSSI or CGI. This way a
 346           URL <code>/foo/S=java/bar/</code> gets translated to
 347           <code>/foo/bar/</code> and the environment variable named
 348           <code>STATUS</code> is set to the value "java".</p>
 349
 350 <div class="example"><pre>
 351 RewriteEngine on
 352 RewriteRule   ^(.*)/<strong>S=([^/]+)</strong>/(.*)    $1/$3 [E=<strong>STATUS:$2</strong>]
 353 </pre></div>
 354         </dd>
 355       </dl>
 356
 357     </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 358 <div class="section">
 359 <h2><a name="uservhosts" id="uservhosts">Virtual Hosts Per User</a></h2>
 360
 361
 362
 363       <dl>
 364         <dt>Description:</dt>
 365
 366         <dd>
 367           <p>Assume that you want to provide
 368           <code>www.<strong>username</strong>.host.domain.com</code>
 369           for the homepage of username via just DNS A records to the
 370           same machine and without any virtualhosts on this
 371           machine.</p>
 372         </dd>
 373
 374         <dt>Solution:</dt>
 375
 376         <dd>
 377           <p>For HTTP/1.0 requests there is no solution, but for
 378           HTTP/1.1 requests which contain a Host: HTTP header we
 379           can use the following ruleset to rewrite
 380           <code>http://www.username.host.com/anypath</code>
 381           internally to <code>/home/username/anypath</code>:</p>
 382
 383 <div class="example"><pre>
 384 RewriteEngine on
 385 RewriteCond   %{<strong>HTTP_HOST</strong>}                 ^www\.<strong>([^.]+)</strong>\.host\.com$
 386 RewriteRule   ^(.*) /home/<strong>%1</strong>$1
 387 </pre></div>
 388
 389 <p>Parentheses used in a <code class="directive"><a href="../mod/mod_rewrite.html#rewritecond">RewriteCond</a></code> are captured into the
 390 backreferences <code>%1</code>, <code>%2</code>, etc, while parentheses
 391 used in <code class="directive"><a href="../mod/mod_rewrite.html#rewriterule">RewriteRule</a></code> are
 392 captured into the backreferences <code>$1</code>, <code>$2</code>,
 393 etc.</p>
 394         </dd>
 395       </dl>
 396
 397     </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 398 <div class="section">
 399 <h2><a name="redirecthome" id="redirecthome">Redirect Homedirs For Foreigners</a></h2>
 400
 401
 402
 403       <dl>
 404         <dt>Description:</dt>
 405
 406         <dd>
 407           <p>We want to redirect homedir URLs to another webserver
 408           <code>www.somewhere.com</code> when the requesting user
 409           does not stay in the local domain
 410           <code>ourdomain.com</code>. This is sometimes used in
 411           virtual host contexts.</p>
 412         </dd>
 413
 414         <dt>Solution:</dt>
 415
 416         <dd>
 417           <p>Just a rewrite condition:</p>
 418
 419 <div class="example"><pre>
 420 RewriteEngine on
 421 RewriteCond   %{REMOTE_HOST}  <strong>!^.+\.ourdomain\.com$</strong>
 422 RewriteRule   ^(/~.+)         http://www.somewhere.com/$1 [R,L]
 423 </pre></div>
 424         </dd>
 425       </dl>
 426
 427     </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 428 <div class="section">
 429 <h2><a name="redirectanchors" id="redirectanchors">Redirecting Anchors</a></h2>
 430
 431
 432
 433       <dl>
 434         <dt>Description:</dt>
 435
 436         <dd>
 437         <p>By default, redirecting to an HTML anchor doesn't work,
 438         because mod_rewrite escapes the <code>#</code> character,
 439         turning it into <code>%23</code>. This, in turn, breaks the
 440         redirection.</p>
 441         </dd>
 442
 443         <dt>Solution:</dt>
 444
 445         <dd>
 446           <p>Use the <code>[NE]</code> flag on the
 447           <code>RewriteRule</code>. NE stands for No Escape.
 448           </p>
 449         </dd>
 450       </dl>
 451
 452     </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 453 <div class="section">
 454 <h2><a name="time-dependent" id="time-dependent">Time-Dependent Rewriting</a></h2>
 455
 456
 457
 458       <dl>
 459         <dt>Description:</dt>
 460
 461         <dd>
 462           <p>When tricks like time-dependent content should happen a
 463           lot of webmasters still use CGI scripts which do for
 464           instance redirects to specialized pages. How can it be done
 465           via <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>?</p>
 466         </dd>
 467
 468         <dt>Solution:</dt>
 469
 470         <dd>
 471           <p>There are a lot of variables named <code>TIME_xxx</code>
 472           for rewrite conditions. In conjunction with the special
 473           lexicographic comparison patterns <code>&lt;STRING</code>,
 474           <code>&gt;STRING</code> and <code>=STRING</code> we can
 475           do time-dependent redirects:</p>
 476
 477 <div class="example"><pre>
 478 RewriteEngine on
 479 RewriteCond   %{TIME_HOUR}%{TIME_MIN} &gt;0700
 480 RewriteCond   %{TIME_HOUR}%{TIME_MIN} &lt;1900
 481 RewriteRule   ^foo\.html$             foo.day.html
 482 RewriteRule   ^foo\.html$             foo.night.html
 483 </pre></div>
 484
 485           <p>This provides the content of <code>foo.day.html</code>
 486           under the URL <code>foo.html</code> from
 487           <code>07:00-19:00</code> and at the remaining time the
 488           contents of <code>foo.night.html</code>. Just a nice
 489           feature for a homepage...</p>
 490         </dd>
 491       </dl>
 492
 493     </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 494 <div class="section">
 495 <h2><a name="backward-compatibility" id="backward-compatibility">Backward Compatibility for YYYY to XXXX migration</a></h2>
 496
 497
 498
 499       <dl>
 500         <dt>Description:</dt>
 501
 502         <dd>
 503           <p>How can we make URLs backward compatible (still
 504           existing virtually) after migrating <code>document.YYYY</code>
 505           to <code>document.XXXX</code>, e.g. after translating a
 506           bunch of <code>.html</code> files to <code>.phtml</code>?</p>
 507         </dd>
 508
 509         <dt>Solution:</dt>
 510
 511         <dd>
 512           <p>We just rewrite the name to its basename and test for
 513           existence of the new extension. If it exists, we take
 514           that name, else we rewrite the URL to its original state.</p>
 515
 516
 517 <div class="example"><pre>
 518 #   backward compatibility ruleset for
 519 #   rewriting document.html to document.phtml
 520 #   when and only when document.phtml exists
 521 #   but no longer document.html
 522 RewriteEngine on
 523 RewriteBase   /~quux/
 524 #   parse out basename, but remember the fact
 525 RewriteRule   ^(.*)\.html$              $1      [C,E=WasHTML:yes]
 526 #   rewrite to document.phtml if exists
 527 #   Note: This is a per-directory example, so %{REQUEST_FILENAME} is the full
 528 #         filesystem path as already mapped by the server.
 529 RewriteCond   %{REQUEST_FILENAME}.phtml -f
 530 RewriteRule   ^(.*)$ $1.phtml                   [S=1]
 531 #   else reverse the previous basename cutout
 532 RewriteCond   %{ENV:WasHTML}            ^yes$
 533 RewriteRule   ^(.*)$ $1.html
 534 </pre></div>
 535         </dd>
 536       </dl>
 537
 538     </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 539 <div class="section">
 540 <h2><a name="old-to-new" id="old-to-new">From Old to New (intern)</a></h2>
 541
 542
 543
 544       <dl>
 545         <dt>Description:</dt>
 546
 547         <dd>
 548           <p>Assume we have recently renamed the page
 549           <code>foo.html</code> to <code>bar.html</code> and now want
 550           to provide the old URL for backward compatibility. Actually
 551           we want that users of the old URL even not recognize that
 552           the pages was renamed.</p>
 553         </dd>
 554
 555         <dt>Solution:</dt>
 556
 557         <dd>
 558           <p>We rewrite the old URL to the new one internally via the
 559           following rule:</p>
 560
 561 <div class="example"><pre>
 562 RewriteEngine  on
 563 RewriteBase    /~quux/
 564 RewriteRule    ^<strong>foo</strong>\.html$  <strong>bar</strong>.html
 565 </pre></div>
 566         </dd>
 567       </dl>
 568
 569     </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 570 <div class="section">
 571 <h2><a name="old-to-new-extern" id="old-to-new-extern">From Old to New (extern)</a></h2>
 572
 573
 574
 575       <dl>
 576         <dt>Description:</dt>
 577
 578         <dd>
 579           <p>Assume again that we have recently renamed the page
 580           <code>foo.html</code> to <code>bar.html</code> and now want
 581           to provide the old URL for backward compatibility. But this
 582           time we want that the users of the old URL get hinted to
 583           the new one, i.e. their browsers Location field should
 584           change, too.</p>
 585         </dd>
 586
 587         <dt>Solution:</dt>
 588
 589         <dd>
 590           <p>We force a HTTP redirect to the new URL which leads to a
 591           change of the browsers and thus the users view:</p>
 592
 593 <div class="example"><pre>
 594 RewriteEngine  on
 595 RewriteBase    /~quux/
 596 RewriteRule    ^<strong>foo</strong>\.html$  <strong>bar</strong>.html  [<strong>R</strong>]
 597 </pre></div>
 598         </dd>
 599       </dl>
 600
 601     </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 602 <div class="section">
 603 <h2><a name="static-to-dynamic" id="static-to-dynamic">From Static to Dynamic</a></h2>
 604
 605
 606
 607       <dl>
 608         <dt>Description:</dt>
 609
 610         <dd>
 611           <p>How can we transform a static page
 612           <code>foo.html</code> into a dynamic variant
 613           <code>foo.cgi</code> in a seamless way, i.e. without notice
 614           by the browser/user.</p>
 615         </dd>
 616
 617         <dt>Solution:</dt>
 618
 619         <dd>
 620           <p>We just rewrite the URL to the CGI-script and force the
 621           handler to be <strong>cgi-script</strong> so that it is
 622           executed as a CGI program.
 623           This way a request to <code>/~quux/foo.html</code>
 624           internally leads to the invocation of
 625           <code>/~quux/foo.cgi</code>.</p>
 626
 627 <div class="example"><pre>
 628 RewriteEngine  on
 629 RewriteBase    /~quux/
 630 RewriteRule    ^foo\.<strong>html</strong>$  foo.<strong>cgi</strong>  [H=<strong>cgi-script</strong>]
 631 </pre></div>
 632         </dd>
 633       </dl>
 634
 635     </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 636 <div class="section">
 637 <h2><a name="blocking-of-robots" id="blocking-of-robots">Blocking of Robots</a></h2>
 638
 639
 640
 641       <dl>
 642         <dt>Description:</dt>
 643
 644         <dd>
 645           <p>How can we block a really annoying robot from
 646           retrieving pages of a specific webarea? A
 647           <code>/robots.txt</code> file containing entries of the
 648           "Robot Exclusion Protocol" is typically not enough to get
 649           rid of such a robot.</p>
 650         </dd>
 651
 652         <dt>Solution:</dt>
 653
 654         <dd>
 655           <p>We use a ruleset which forbids the URLs of the webarea
 656           <code>/~quux/foo/arc/</code> (perhaps a very deep
 657           directory indexed area where the robot traversal would
 658           create big server load). We have to make sure that we
 659           forbid access only to the particular robot, i.e. just
 660           forbidding the host where the robot runs is not enough.
 661           This would block users from this host, too. We accomplish
 662           this by also matching the User-Agent HTTP header
 663           information.</p>
 664
 665 <div class="example"><pre>
 666 RewriteCond %{HTTP_USER_AGENT}   ^<strong>NameOfBadRobot</strong>.*
 667 RewriteCond %{REMOTE_ADDR}       ^<strong>123\.45\.67\.[8-9]</strong>$
 668 RewriteRule ^<strong>/~quux/foo/arc/</strong>.+   -   [<strong>F</strong>]
 669 </pre></div>
 670         </dd>
 671       </dl>
 672
 673     </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 674 <div class="section">
 675 <h2><a name="blocked-inline-images" id="blocked-inline-images">Forbidding Image "Hotlinking"</a></h2>
 676
 677
 678
 679       <dl>
 680         <dt>Description:</dt>
 681
 682         <dd>
 683           <p>The following technique forbids the practice of other sites
 684           including your images inline in their pages. This practice is
 685           often referred to as "hotlinking", and results in
 686           your bandwidth being used to serve content for someone else's
 687           site.</p>
 688         </dd>
 689
 690         <dt>Solution:</dt>
 691
 692         <dd>
 693           <p>This technique relies on the value of the
 694           <code>HTTP_REFERER</code> variable, which is optional. As
 695           such, it's possible for some people to circumvent this
 696           limitation. However, most users will experience the failed
 697           request, which should, over time, result in the image being
 698           removed from that other site.</p>
 699           <p>There are several ways that you can handle this
 700           situation.</p>
 701
 702     <p>In this first example, we simply deny the request, if it didn't
 703     initiate from a page on our site. For the purpose of this example,
 704     we assume that our site is <code>www.example.com</code>.</p>
 705
 706 <div class="example"><pre>
 707 RewriteCond %{HTTP_REFERER} <strong>!^$</strong>
 708 RewriteCond %{HTTP_REFERER} !www.example.com [NC]
 709 RewriteRule <strong>\.(gif|jpg|png)$</strong>    -   [F,NC]
 710 </pre></div>
 711
 712     <p>In this second example, instead of failing the request, we display
 713     an alternate image instead.</p>
 714
 715 <div class="example"><pre>
 716 RewriteCond %{HTTP_REFERER} <strong>!^$</strong>
 717 RewriteCond %{HTTP_REFERER} !www.example.com [NC]
 718 RewriteRule <strong>\.(gif|jpg|png)$</strong>    /images/go-away.png   [R,NC]
 719 </pre></div>
 720
 721     <p>In the third example, we redirect the request to an image on some
 722     third-party site.</p>
 723
 724 <div class="example"><pre>
 725 RewriteCond %{HTTP_REFERER} <strong>!^$</strong>
 726 RewriteCond %{HTTP_REFERER} !www.example.com [NC]
 727 RewriteRule <strong>\.(gif|jpg|png)$</strong> http://other.site.com/image.gif   [R,NC]
 728 </pre></div>
 729
 730     <p>Of these techniques, the last two tend to be the most effective
 731     in getting people to stop hotlinking your images, because they will
 732     simply not see the image that they expected to see.</p>
 733
 734         </dd>
 735       </dl>
 736
 737     </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 738 <div class="section">
 739 <h2><a name="proxy-deny" id="proxy-deny">Proxy Deny</a></h2>
 740
 741
 742
 743       <dl>
 744         <dt>Description:</dt>
 745
 746         <dd>
 747           <p>How can we forbid a certain host or even a user of a
 748           special host from using the Apache proxy?</p>
 749         </dd>
 750
 751         <dt>Solution:</dt>
 752
 753         <dd>
 754           <p>We first have to make sure <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>
 755           is below(!) <code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code> in the Configuration
 756           file when compiling the Apache webserver. This way it gets
 757           called <em>before</em> <code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code>. Then we
 758           configure the following for a host-dependent deny...</p>
 759
 760 <div class="example"><pre>
 761 RewriteCond %{REMOTE_HOST} <strong>^badhost\.mydomain\.com$</strong>
 762 RewriteRule !^http://[^/.]\.mydomain.com.*  - [F]
 763 </pre></div>
 764
 765           <p>...and this one for a user@host-dependent deny:</p>
 766
 767 <div class="example"><pre>
 768 RewriteCond %{REMOTE_IDENT}@%{REMOTE_HOST}  <strong>^badguy@badhost\.mydomain\.com$</strong>
 769 RewriteRule !^http://[^/.]\.mydomain.com.*  - [F]
 770 </pre></div>
 771         </dd>
 772       </dl>
 773
 774     </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 775 <div class="section">
 776 <h2><a name="external-rewriting" id="external-rewriting">External Rewriting Engine</a></h2>
 777
 778
 779
 780       <dl>
 781         <dt>Description:</dt>
 782
 783         <dd>
 784           <p>A FAQ: How can we solve the FOO/BAR/QUUX/etc.
 785           problem? There seems no solution by the use of
 786           <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>...</p>
 787         </dd>
 788
 789         <dt>Solution:</dt>
 790
 791         <dd>
 792           <p>Use an external <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code>, i.e. a program which acts
 793           like a <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code>. It is run once on startup of Apache
 794           receives the requested URLs on <code>STDIN</code> and has
 795           to put the resulting (usually rewritten) URL on
 796           <code>STDOUT</code> (same order!).</p>
 797
 798 <div class="example"><pre>
 799 RewriteEngine on
 800 RewriteMap    quux-map       <strong>prg:</strong>/path/to/map.quux.pl
 801 RewriteRule   ^/~quux/(.*)$  /~quux/<strong>${quux-map:$1}</strong>
 802 </pre></div>
 803
 804 <div class="example"><pre>
 805 #!/path/to/perl
 806
 807 #   disable buffered I/O which would lead
 808 #   to deadloops for the Apache server
 809 $| = 1;
 810
 811 #   read URLs one per line from stdin and
 812 #   generate substitution URL on stdout
 813 while (&lt;&gt;) {
 814     s|^foo/|bar/|;
 815     print $_;
 816 }
 817 </pre></div>
 818
 819           <p>This is a demonstration-only example and just rewrites
 820           all URLs <code>/~quux/foo/...</code> to
 821           <code>/~quux/bar/...</code>. Actually you can program
 822           whatever you like. But notice that while such maps can be
 823           <strong>used</strong> also by an average user, only the
 824           system administrator can <strong>define</strong> it.</p>
 825         </dd>
 826       </dl>
 827
 828     </div></div>
 829 <div class="bottomlang">
 830 <p><span>Available Languages: </span><a href="../en/rewrite/rewrite_guide.html" title="English">&nbsp;en&nbsp;</a></p>
 831 </div><div id="footer">
 832 <p class="apache">Copyright 2009 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>
 833 <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>
 834 </body></html>