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23 <manualpage metafile="expr.xml.meta">
25 <title>Expressions in Apache HTTP Server</title>
28 <p>Historically, there are several syntax variants for expressions used to express
29 a condition in the different modules of the Apache HTTP Server.
30 There is some ongoing effort to only use a single variant, called <em>ap_expr</em>,
31 for all configuration directives.
32 This document describes the <em>ap_expr</em> expression parser.
34 <p>The <em>ap_expr</em> expression is intended to replace most other
35 expression variants in HTTPD. For example, the deprecated
36 <directive module="mod_ssl">SSLRequire</directive> expressions can be
37 replaced by <a href="mod/mod_authz_core.html#reqexpr">Require expr</a>.
41 <seealso><directive module="core" type="section">If</directive></seealso>
42 <seealso><directive module="core" type="section">ElseIf</directive></seealso>
43 <seealso><directive module="core" type="section">Else</directive></seealso>
44 <seealso><directive module="mod_auth_basic">AuthBasicFake</directive></seealso>
45 <seealso><directive module="mod_auth_form">AuthFormLoginRequiredLocation</directive></seealso>
46 <seealso><directive module="mod_auth_form">AuthFormLoginSuccessLocation</directive></seealso>
47 <seealso><directive module="mod_auth_form">AuthFormLogoutLocation</directive></seealso>
48 <seealso><directive module="mod_rewrite">RewriteCond</directive></seealso>
49 <seealso><directive module="mod_setenvif">SetEnvIfExpr</directive></seealso>
50 <seealso><directive module="mod_headers">Header</directive></seealso>
51 <seealso><directive module="mod_headers">RequestHeader</directive></seealso>
52 <seealso><directive module="mod_filter">FilterProvider</directive></seealso>
53 <seealso><a href="mod/mod_authz_core.html#reqexpr">Require expr</a></seealso>
54 <seealso><directive module="mod_ssl">SSLRequire</directive></seealso>
55 <seealso><directive module="mod_log_debug">LogMessage</directive></seealso>
56 <seealso><module>mod_include</module></seealso>
58 <section id="grammar">
59 <title>Grammar in Backus-Naur Form notation</title>
60 <p><a href="http://en.wikipedia.org/wiki/Backus%E2%80%93Naur_Form">Backus-Naur Form</a> (BNF) is a notation
61 technique for context-free grammars, often used to describe the syntax of languages used in computing.
62 In most cases, expressions are used to express boolean values.
63 For these, the starting point in the BNF is <code>expr</code>. However, a few directives
64 like <directive module="mod_log_debug">LogMessage</directive> accept expressions
65 that evaluate to a string value. For those, the starting point in the BNF is <code>string</code>.
69 expr ::= "<strong>true</strong>" | "<strong>false</strong>"
70 | "<strong>!</strong>" expr
71 | expr "<strong>&&</strong>" expr
72 | expr "<strong>||</strong>" expr
73 | "<strong>(</strong>" expr "<strong>)</strong>"
80 | word "<strong>in</strong>" "<strong>{</strong>" wordlist "<strong>}</strong>"
81 | word "<strong>in</strong>" listfunction
82 | word "<strong>=~</strong>" regex
83 | word "<strong>!~</strong>" regex
86 stringcomp ::= word "<strong>==</strong>" word
87 | word "<strong>!=</strong>" word
88 | word "<strong><</strong>" word
89 | word "<strong><=</strong>" word
90 | word "<strong>></strong>" word
91 | word "<strong>>=</strong>" word
93 integercomp ::= word "<strong>-eq</strong>" word | word "<strong>eq</strong>" word
94 | word "<strong>-ne</strong>" word | word "<strong>ne</strong>" word
95 | word "<strong>-lt</strong>" word | word "<strong>lt</strong>" word
96 | word "<strong>-le</strong>" word | word "<strong>le</strong>" word
97 | word "<strong>-gt</strong>" word | word "<strong>gt</strong>" word
98 | word "<strong>-ge</strong>" word | word "<strong>ge</strong>" word
101 | wordlist "<strong>,</strong>" word
103 word ::= word "<strong>.</strong>" word
105 | "<strong>'</strong>" string "<strong>'</strong>"
106 | "<strong>"</strong>" string "<strong>"</strong>"
111 string ::= stringpart
114 stringpart ::= cstring
121 variable ::= "<strong>%{</strong>" varname "<strong>}</strong>"
122 | "<strong>%{</strong>" funcname "<strong>:</strong>" funcargs "<strong>}</strong>"
124 rebackref ::= "<strong>$</strong>" [0-9]
126 function ::= funcname "<strong>(</strong>" word "<strong>)</strong>"
128 listfunction ::= listfuncname "<strong>(</strong>" word "<strong>)</strong>"
135 <title>Variables</title>
137 <p>The expression parser provides a number of variables of the form
138 <code>%{HTTP_HOST}</code>. Note that the value of a variable may depend
139 on the phase of the request processing in which it is evaluated. For
140 example, an expression used in an <directive><If ></directive>
141 directive is evaluated before authentication is done. Therefore,
142 <code>%{REMOTE_USER}</code> will not be set in this case.</p>
144 <p>The following variables provide the values of the named HTTP request
145 headers. The values of other headers can be obtained with the
146 <code>req</code> <a href="#functions">function</a>. Using these
147 variables may cause the header name to be added to the Vary
148 header of the HTTP response, except where otherwise noted for the
149 directive accepting the expression. The <code>req_novary</code>
150 <a href="#functions">function</a> may be used to circumvent this
153 <table border="1" style="zebra">
154 <columnspec><column width="1"/></columnspec>
156 <tr><th>Name</th></tr>
157 <tr><td><code>HTTP_ACCEPT</code></td></tr>
158 <tr><td><code>HTTP_FORWARDED</code></td></tr>
159 <tr><td><code>HTTP_HOST</code></td></tr>
160 <tr><td><code>HTTP_PROXY_CONNECTION</code></td></tr>
161 <tr><td><code>HTTP_REFERER</code></td></tr>
162 <tr><td><code>HTTP_USER_AGENT</code></td></tr>
166 <p>Other request related variables</p>
168 <table border="1" style="zebra">
169 <columnspec><column width=".4"/><column width=".6"/></columnspec>
171 <tr><th>Name</th><th>Description</th></tr>
172 <tr><td><code>REQUEST_METHOD</code></td>
173 <td>The HTTP method of the incoming request (e.g.
174 <code>GET</code>)</td></tr>
175 <tr><td><code>REQUEST_SCHEME</code></td>
176 <td>The scheme part of the request's URI</td></tr>
177 <tr><td><code>REQUEST_URI</code></td>
178 <td>The path part of the request's URI</td></tr>
179 <tr><td><code>DOCUMENT_URI</code></td>
180 <td>Same as REQUEST_URI</td></tr>
181 <tr><td><code>REQUEST_FILENAME</code></td>
182 <td>The full local filesystem path to the file or script matching the
183 request, if this has already been determined by the server at the
184 time <code>REQUEST_FILENAME</code> is referenced. Otherwise, such
185 as when used in virtual host context, the same value as
186 <code>REQUEST_URI</code> </td></tr>
187 <tr><td><code>SCRIPT_FILENAME</code></td>
188 <td>Same as <code>REQUEST_FILENAME</code></td></tr>
189 <tr><td><code>LAST_MODIFIED</code></td>
190 <td>The date and time of last modification of the file in the format
191 <code>20101231235959</code>, if this has already been determined by
192 the server at the time <code>LAST_MODIFIED</code> is referenced.
194 <tr><td><code>SCRIPT_USER</code></td>
195 <td>The user name of the owner of the script.</td></tr>
196 <tr><td><code>SCRIPT_GROUP</code></td>
197 <td>The group name of the group of the script.</td></tr>
198 <tr><td><code>PATH_INFO</code></td>
199 <td>The trailing path name information, see
200 <directive module="core">AcceptPathInfo</directive></td></tr>
201 <tr><td><code>QUERY_STRING</code></td>
202 <td>The query string of the current request</td></tr>
203 <tr><td><code>IS_SUBREQ</code></td>
204 <td>"<code>true</code>" if the current request is a subrequest,
205 "<code>false</code>" otherwise</td></tr>
206 <tr><td><code>THE_REQUEST</code></td>
207 <td>The complete request line (e.g.,
208 "<code>GET /index.html HTTP/1.1</code>")</td></tr>
209 <tr><td><code>REMOTE_ADDR</code></td>
210 <td>The IP address of the remote host</td></tr>
211 <tr><td><code>REMOTE_HOST</code></td>
212 <td>The host name of the remote host</td></tr>
213 <tr><td><code>REMOTE_USER</code></td>
214 <td>The name of the authenticated user (if any)</td></tr>
215 <tr><td><code>REMOTE_IDENT</code></td>
216 <td>The user name set by <module>mod_ident</module></td></tr>
217 <tr><td><code>SERVER_NAME</code></td>
218 <td>The <directive module="core">ServerName</directive> of
219 the current vhost</td></tr>
220 <tr><td><code>SERVER_PORT</code></td>
221 <td>The server port of the current vhost, see
222 <directive module="core">ServerName</directive></td></tr>
223 <tr><td><code>SERVER_ADMIN</code></td>
224 <td>The <directive module="core">ServerAdmin</directive> of
225 the current vhost</td></tr>
226 <tr><td><code>SERVER_PROTOCOL</code></td>
227 <td>The protocol used by the request (e.g. HTTP/1.1). In some types of
228 internal subrequests, this variable has the value
229 <code>INCLUDED</code>.</td></tr>
230 <tr><td><code>SERVER_PROTOCOL_VERSION</code></td>
231 <td>A number that encodes the HTTP version of the request:
232 <code>1000 * major + minor</code>. For example, <code>1001</code>
233 corresponds to HTTP/1.1 and <code>9</code> corresponds
234 to HTTP/0.9</td></tr>
235 <tr><td><code>SERVER_PROTOCOL_VERSION_MAJOR</code></td>
236 <td>The major version part of the HTTP version of the request,
237 e.g. <code>1</code> for HTTP/1.0</td></tr>
238 <tr><td><code>SERVER_PROTOCOL_VERSION_MINOR</code></td>
239 <td>The minor version part of the HTTP version of the request,
240 e.g. <code>0</code> for HTTP/1.0</td></tr>
241 <tr><td><code>DOCUMENT_ROOT</code></td>
242 <td>The <directive module="core">DocumentRoot</directive> of
243 the current vhost</td></tr>
244 <tr><td><code>AUTH_TYPE</code></td>
245 <td>The configured <directive module="mod_authn_core">AuthType</directive>
246 (e.g. "<code>basic</code>")</td></tr>
247 <tr><td><code>CONTENT_TYPE</code></td>
248 <td>The content type of the response</td></tr>
249 <tr><td><code>HANDLER</code></td>
250 <td>The name of the <a href="handler.html">handler</a> creating
251 the response</td></tr>
252 <tr><td><code>HTTPS</code></td>
253 <td>"<code>on</code>" if the request uses https,
254 "<code>off</code>" otherwise</td></tr>
255 <tr><td><code>IPV6</code></td>
256 <td>"<code>on</code>" if the connection uses IPv6,
257 "<code>off</code>" otherwise</td></tr>
258 <tr><td><code>REQUEST_STATUS</code></td>
259 <td>The HTTP error status of the request</td></tr>
260 <tr><td><code>REQUEST_LOG_ID</code></td>
261 <td>The error log id of the request (see
262 <directive module="core">ErrorLogFormat</directive>)</td></tr>
263 <tr><td><code>CONN_LOG_ID</code></td>
264 <td>The error log id of the connection (see
265 <directive module="core">ErrorLogFormat</directive>)</td></tr>
266 <tr><td><code>CONN_REMOTE_ADDR</code></td>
267 <td>The peer IP address of the connection (see the
268 <module>mod_remoteip</module> module)</td></tr>
272 <p>Misc variables</p>
274 <table border="1" style="zebra">
275 <columnspec><column width=".4"/><column width=".6"/></columnspec>
277 <tr><th>Name</th><th>Description</th></tr>
278 <tr><td><code>TIME_YEAR</code></td>
279 <td>The current year (e.g. <code>2010</code>)</td></tr>
280 <tr><td><code>TIME_MON</code></td>
281 <td>The current month (<code>1</code>, ..., <code>12</code>)</td></tr>
282 <tr><td><code>TIME_DAY</code></td>
283 <td>The current day of the month</td></tr>
284 <tr><td><code>TIME_HOUR</code></td>
285 <td>The hour part of the current time
286 (<code>0</code>, ..., <code>23</code>)</td></tr>
287 <tr><td><code>TIME_MIN</code></td>
288 <td>The minute part of the current time </td></tr>
289 <tr><td><code>TIME_SEC</code></td>
290 <td>The second part of the current time </td></tr>
291 <tr><td><code>TIME_WDAY</code></td>
292 <td>The day of the week (starting with <code>0</code>
293 for Sunday)</td></tr>
294 <tr><td><code>TIME</code></td>
295 <td>The date and time in the format <code>20101231235959</code></td></tr>
296 <tr><td><code>SERVER_SOFTWARE</code></td>
297 <td>The server version string</td></tr>
298 <tr><td><code>API_VERSION</code></td>
299 <td>The date of the API version (module magic number)</td></tr>
302 <p>Some modules register additional variables, see e.g. <module>mod_ssl</module>.</p>
307 <title>Binary operators</title>
309 <p>With the exception of some built-in comparison operators, binary
310 operators have the form "<code>-[a-zA-Z][a-zA-Z0-9_]+</code>", i.e. a
311 minus and at least two characters. The name is not case sensitive.
312 Modules may register additional binary operators.</p>
315 <title>Comparison operators</title>
317 <table border="1" style="zebra">
318 <columnspec><column width=".2"/><column width=".2"/><column width=".6"/></columnspec>
320 <tr><th>Name</th><th>Alternative</th> <th>Description</th></tr>
321 <tr><td><code>==</code></td>
322 <td><code>=</code></td>
323 <td>String equality</td></tr>
324 <tr><td><code>!=</code></td>
326 <td>String inequality</td></tr>
327 <tr><td><code><</code></td>
329 <td>String less than</td></tr>
330 <tr><td><code><=</code></td>
332 <td>String less than or equal</td></tr>
333 <tr><td><code>></code></td>
335 <td>String greater than</td></tr>
336 <tr><td><code>>=</code></td>
338 <td>String greater than or equal</td></tr>
339 <tr><td><code>-eq</code></td>
340 <td><code>eq</code></td>
341 <td>Integer equality</td></tr>
342 <tr><td><code>-ne</code></td>
343 <td><code>ne</code></td>
344 <td>Integer inequality</td></tr>
345 <tr><td><code>-lt</code></td>
346 <td><code>lt</code></td>
347 <td>Integer less than</td></tr>
348 <tr><td><code>-le</code></td>
349 <td><code>le</code></td>
350 <td>Integer less than or equal</td></tr>
351 <tr><td><code>-gt</code></td>
352 <td><code>gt</code></td>
353 <td>Integer greater than</td></tr>
354 <tr><td><code>-ge</code></td>
355 <td><code>ge</code></td>
356 <td>Integer greater than or equal</td></tr>
360 <section id="binaryother">
361 <title>Other binary operators</title>
363 <table border="1" style="zebra">
364 <columnspec><column width=".2"/><column width=".8"/></columnspec>
366 <tr><th>Name</th><th>Description</th></tr>
367 <tr><td><code>-ipmatch</code></td>
368 <td>IP address matches address/netmask</td></tr>
369 <tr><td><code>-strmatch</code></td>
370 <td>left string matches pattern given by right string (containing
371 wildcards *, ?, [])</td></tr>
372 <tr><td><code>-strcmatch</code></td>
373 <td>same as <code>-strmatch</code>, but case insensitive</td></tr>
374 <tr><td><code>-fnmatch</code></td>
375 <td>same as <code>-strmatch</code>, but slashes are not matched by
383 <title>Unary operators</title>
385 <p>Unary operators take one argument and have the form
386 "<code>-[a-zA-Z]</code>", i.e. a minus and one character.
387 The name <em>is</em> case sensitive.
388 Modules may register additional unary operators.</p>
390 <table border="1" style="zebra">
391 <columnspec><column width=".2"/><column width=".2"/><column width=".6"/></columnspec>
393 <tr><th>Name</th><th>Description</th><th>Restricted</th></tr>
394 <tr><td><code>-d</code></td>
395 <td>The argument is treated as a filename.
396 True if the file exists and is a directory</td><td>yes</td></tr>
397 <tr><td><code>-e</code></td>
398 <td>The argument is treated as a filename.
399 True if the file (or dir or special) exists</td><td>yes</td></tr>
400 <tr><td><code>-f</code></td>
401 <td>The argument is treated as a filename.
402 True if the file exists and is regular file</td><td>yes</td></tr>
403 <tr><td><code>-s</code></td>
404 <td>The argument is treated as a filename.
405 True if the file exists and is not empty</td><td>yes</td></tr>
406 <tr><td><code>-L</code></td>
407 <td>The argument is treated as a filename.
408 True if the file exists and is symlink</td><td>yes</td></tr>
409 <tr><td><code>-h</code></td>
410 <td>The argument is treated as a filename.
411 True if the file exists and is symlink
412 (same as <code>-L</code>)</td><td>yes</td></tr>
413 <tr><td><code>-F</code></td>
414 <td>True if string is a valid file, accessible via all the server's
415 currently-configured access controls for that path. This uses an
416 internal subrequest to do the check, so use it with care - it can
417 impact your server's performance!</td><td></td></tr>
418 <tr><td><code>-U</code></td>
419 <td>True if string is a valid URL, accessible via all the server's
420 currently-configured access controls for that path. This uses an
421 internal subrequest to do the check, so use it with care - it can
422 impact your server's performance!</td><td></td></tr>
423 <tr><td><code>-A</code></td>
424 <td>Alias for <code>-U</code></td><td></td></tr>
425 <tr><td><code>-n</code></td>
426 <td>True if string is not empty</td><td></td></tr>
427 <tr><td><code>-z</code></td>
428 <td>True if string is empty</td><td></td></tr>
429 <tr><td><code>-T</code></td>
430 <td>False if string is empty, "<code>0</code>", "<code>off</code>",
431 "<code>false</code>", or "<code>no</code>" (case insensitive).
432 True otherwise.</td><td></td></tr>
433 <tr><td><code>-R</code></td>
434 <td>Same as "<code>%{REMOTE_ADDR} -ipmatch ...</code>", but more efficient
438 <p>The operators marked as "restricted" are not available in some modules
439 like <module>mod_include</module>.</p>
442 <section id="functions">
443 <title>Functions</title>
445 <p>Normal string-valued functions take one string as argument and return
446 a string. Functions names are not case sensitive.
447 Modules may register additional functions.</p>
449 <table border="1" style="zebra">
450 <columnspec><column width=".2"/><column width=".8"/></columnspec>
452 <tr><th>Name</th><th>Description</th><th>Restricted</th></tr>
453 <tr><td><code>req</code>, <code>http</code></td>
454 <td>Get HTTP request header; header names may be added to the Vary
455 header, see below</td><td></td></tr>
456 <tr><td><code>req_novary</code></td>
457 <td>Same as <code>req</code>, but header names will not be added to the
458 Vary header</td><td></td></tr>
459 <tr><td><code>resp</code></td>
460 <td>Get HTTP response header</td><td></td></tr>
461 <tr><td><code>reqenv</code></td>
462 <td>Lookup request environment variable (as a shortcut, <code>v</code> can be used too to access variables).</td><td></td></tr>
463 <tr><td><code>osenv</code></td>
464 <td>Lookup operating system environment variable</td><td></td></tr>
465 <tr><td><code>note</code></td>
466 <td>Lookup request note</td><td></td></tr>
467 <tr><td><code>env</code></td>
468 <td>Return first match of <code>note</code>, <code>reqenv</code>,
469 <code>osenv</code></td><td></td></tr>
470 <tr><td><code>tolower</code></td>
471 <td>Convert string to lower case</td><td></td></tr>
472 <tr><td><code>toupper</code></td>
473 <td>Convert string to upper case</td><td></td></tr>
474 <tr><td><code>escape</code></td>
475 <td>Escape special characters in %hex encoding</td><td></td></tr>
476 <tr><td><code>unescape</code></td>
477 <td>Unescape %hex encoded string, leaving encoded slashes alone;
478 return empty string if %00 is found</td><td></td></tr>
479 <tr><td><code>base64</code></td>
480 <td>Encode the string using base64 encoding</td><td></td></tr>
481 <tr><td><code>unbase64</code></td>
482 <td>Decode base64 encoded string, return truncated string if 0x00 is
483 found</td><td></td></tr>
484 <tr><td><code>md5</code></td>
485 <td>Hash the string using MD5, then encode the hash with hexadecimal
486 encoding</td><td></td></tr>
487 <tr><td><code>sha1</code></td>
488 <td>Hash the string using SHA1, then encode the hash with hexadecimal
489 encoding</td><td></td></tr>
490 <tr><td><code>file</code></td>
491 <td>Read contents from a file</td><td>yes</td></tr>
492 <tr><td><code>filesize</code></td>
493 <td>Return size of a file (or 0 if file does not exist or is not
494 regular file)</td><td>yes</td></tr>
498 <p>The functions marked as "restricted" are not available in some modules
499 like <module>mod_include</module>.</p>
501 <p>When the functions <code>req</code> or <code>http</code> are used,
502 the header name will automatically be added to the Vary header of the
503 HTTP response, except where otherwise noted for the directive accepting
504 the expression. The <code>req_novary</code> function can be used to
505 prevent names from being added to the Vary header.</p>
507 <p>In addition to string-valued functions, there are also list-valued functions which
508 take one string as argument and return a wordlist, i.e. a list of strings. The wordlist
509 can be used with the special <code>-in</code> operator.
510 Functions names are not case sensitive.
511 Modules may register additional functions.</p>
513 <p>There are no built-in list-valued functions. <module>mod_ssl</module>
514 provides <code>PeerExtList</code>. See the description of
515 <directive module="mod_ssl">SSLRequire</directive> for details
516 (but <code>PeerExtList</code> is also usable outside
517 of <directive module="mod_ssl">SSLRequire</directive>).</p>
521 <section id="examples">
523 <title>Example expressions</title>
524 <p>The following examples show how expressions might be used to evaluate requests:</p>
525 <!-- This section should probably be extended with more, useful examples -->
526 <highlight language="config">
527 # Compare the host name to example.com and redirect to www.example.com if it matches
528 <If "%{HTTP_HOST} == 'example.com'">
529 Redirect permanent / http://www.example.com/
532 # Force text/plain if requesting a file with the query string contains 'forcetext'
533 <If "%{QUERY_STRING} =~ /forcetext/">
537 # Only allow access to this content during business hours
538 <Directory "/foo/bar/business">
539 Require expr %{TIME_HOUR} -gt 9 && %{TIME_HOUR} -lt 17
547 <table border="1" style="zebra">
548 <columnspec><column width=".2"/><column width=".2"/><column width=".6"/></columnspec>
550 <tr><th>Name</th><th>Alternative</th> <th>Description</th></tr>
551 <tr><td><code>-in</code></td>
552 <td><code>in</code></td>
553 <td>string contained in string list</td></tr>
554 <tr><td><code>/regexp/</code></td>
555 <td><code>m#regexp#</code></td>
556 <td>Regular expression (the second form allows different delimiters than /)</td></tr>
557 <tr><td><code>/regexp/i</code></td>
558 <td><code>m#regexp#i</code></td>
559 <td>Case insensitive regular expression</td></tr>
560 <tr><td><code>$0 ... $9</code></td>
562 <td>Regular expression backreferences</td></tr>
565 <section id="rebackref">
566 <title>Regular expression backreferences</title>
567 <p>The strings <code>$0</code> ... <code>$9</code> allow to reference
568 the capture groups from a previously executed, successfully
569 matching regular expressions. They can normally only be used in the
570 same expression as the matching regex, but some modules allow special
576 <section id="sslrequire">
577 <title>Comparison with SSLRequire</title>
578 <p>The <em>ap_expr</em> syntax is mostly a superset of the syntax of the
579 deprecated <directive module="mod_ssl">SSLRequire</directive> directive.
580 The differences are described in <directive
581 module="mod_ssl">SSLRequire</directive>'s documentation.</p>
584 <section id="compatibility">
585 <title>Version History</title>
586 <p>The <code>req_novary</code> <a href="#functions">function</a>
587 is available for versions 2.4.4 and later.</p>
588 <p>The <code>SERVER_PROTOCOL_VERSION</code>,
589 <code>SERVER_PROTOCOL_VERSION_MAJOR</code> and
590 <code>SERVER_PROTOCOL_VERSION_MINOR</code>
591 <a href="#vars">variables</a>
592 are available for versions 2.5.0 and later.</p>