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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
29 used to express a condition in the different modules of the Apache
30 HTTP Server. There is some ongoing effort to only use a single
31 variant, called <em>ap_expr</em>, 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 <directive
36 module="mod_ssl">SSLRequire</directive> expressions can be replaced
37 by <a href="mod/mod_authz_core.html#reqexpr">Require expr</a>. </p>
40 <seealso><directive module="core" type="section">If</directive></seealso>
41 <seealso><directive module="core" type="section">ElseIf</directive></seealso>
42 <seealso><directive module="core" type="section">Else</directive></seealso>
43 <seealso><directive module="core">ErrorDocument</directive></seealso>
44 <seealso><directive module="mod_alias">Alias</directive></seealso>
45 <seealso><directive module="mod_alias">ScriptAlias</directive></seealso>
46 <seealso><directive module="mod_alias">Redirect</directive></seealso>
47 <seealso><directive module="mod_auth_basic">AuthBasicFake</directive></seealso>
48 <seealso><directive module="mod_auth_form">AuthFormLoginRequiredLocation</directive></seealso>
49 <seealso><directive module="mod_auth_form">AuthFormLoginSuccessLocation</directive></seealso>
50 <seealso><directive module="mod_auth_form">AuthFormLogoutLocation</directive></seealso>
51 <seealso><directive module="mod_authn_core">AuthName</directive></seealso>
52 <seealso><directive module="mod_authn_core">AuthType</directive></seealso>
53 <seealso><directive module="mod_rewrite">RewriteCond</directive></seealso>
54 <seealso><directive module="mod_setenvif">SetEnvIfExpr</directive></seealso>
55 <seealso><directive module="mod_headers">Header</directive></seealso>
56 <seealso><directive module="mod_headers">RequestHeader</directive></seealso>
57 <seealso><directive module="mod_filter">FilterProvider</directive></seealso>
58 <seealso><directive module="mod_crypto">CryptoKey</directive></seealso>
59 <seealso><directive module="mod_crypto">CryptoIV</directive></seealso>
60 <seealso><a href="mod/mod_authz_core.html#reqexpr">Require expr</a></seealso>
61 <seealso><a href="mod/mod_authnz_ldap.html#requser">Require ldap-user</a></seealso>
62 <seealso><a href="mod/mod_authnz_ldap.html#reqgroup">Require ldap-group</a></seealso>
63 <seealso><a href="mod/mod_authnz_ldap.html#reqdn">Require ldap-dn</a></seealso>
64 <seealso><a href="mod/mod_authnz_ldap.html#reqattribute">Require ldap-attribute</a></seealso>
65 <seealso><a href="mod/mod_authnz_ldap.html#reqfilter">Require ldap-filter</a></seealso>
66 <seealso><a href="mod/mod_authnz_ldap.html#reqsearch">Require ldap-search</a></seealso>
67 <seealso><a href="mod/mod_authz_dbd.html#reqgroup">Require dbd-group</a></seealso>
68 <seealso><a href="mod/mod_authz_dbm.html#reqgroup">Require dbm-group</a></seealso>
69 <seealso><a href="mod/mod_authz_groupfile.html#reqgroup">Require group</a></seealso>
70 <seealso><a href="mod/mod_authz_host.html#reqhost">Require host</a></seealso>
71 <seealso><directive module="mod_ssl">SSLRequire</directive></seealso>
72 <seealso><directive module="mod_log_debug">LogMessage</directive></seealso>
73 <seealso><module>mod_include</module></seealso>
75 <section id="grammar">
76 <title>Grammar in Backus-Naur Form notation</title>
78 href="http://en.wikipedia.org/wiki/Backus%E2%80%93Naur_Form">Backus-Naur
79 Form</a> (BNF) is a notation technique for context-free grammars,
80 often used to describe the syntax of languages used in computing.
81 In most cases, expressions are used to express boolean values.
82 For these, the starting point in the BNF is <code>expr</code>.
83 However, a few directives like <directive
84 module="mod_log_debug">LogMessage</directive> accept expressions
85 that evaluate to a string value. For those, the starting point in
86 the BNF is <code>string</code>.
90 expr ::= "<strong>true</strong>" | "<strong>false</strong>"
91 | "<strong>!</strong>" expr
92 | expr "<strong>&&</strong>" expr
93 | expr "<strong>||</strong>" expr
94 | "<strong>(</strong>" expr "<strong>)</strong>"
101 | word "<strong>in</strong>" "<strong>{</strong>" wordlist "<strong>}</strong>"
102 | word "<strong>in</strong>" listfunction
103 | word "<strong>=~</strong>" regex
104 | word "<strong>!~</strong>" regex
107 stringcomp ::= word "<strong>==</strong>" word
108 | word "<strong>!=</strong>" word
109 | word "<strong><</strong>" word
110 | word "<strong><=</strong>" word
111 | word "<strong>></strong>" word
112 | word "<strong>>=</strong>" word
114 integercomp ::= word "<strong>-eq</strong>" word | word "<strong>eq</strong>" word
115 | word "<strong>-ne</strong>" word | word "<strong>ne</strong>" word
116 | word "<strong>-lt</strong>" word | word "<strong>lt</strong>" word
117 | word "<strong>-le</strong>" word | word "<strong>le</strong>" word
118 | word "<strong>-gt</strong>" word | word "<strong>gt</strong>" word
119 | word "<strong>-ge</strong>" word | word "<strong>ge</strong>" word
122 | wordlist "<strong>,</strong>" word
124 word ::= word "<strong>.</strong>" word
126 | "<strong>'</strong>" string "<strong>'</strong>"
127 | "<strong>"</strong>" string "<strong>"</strong>"
132 string ::= stringpart
135 stringpart ::= cstring
142 variable ::= "<strong>%{</strong>" varname "<strong>}</strong>"
143 | "<strong>%{</strong>" funcname "<strong>:</strong>" funcargs "<strong>}</strong>"
145 rebackref ::= "<strong>$</strong>" [0-9]
147 function ::= funcname "<strong>(</strong>" wordlist "<strong>)</strong>"
149 listfunction ::= listfuncname "<strong>(</strong>" word "<strong>)</strong>"
156 <title>Variables</title>
158 <p>The expression parser provides a number of variables of the form
159 <code>%{HTTP_HOST}</code>. Note that the value of a variable may depend
160 on the phase of the request processing in which it is evaluated. For
161 example, an expression used in an <directive><If ></directive>
162 directive is evaluated before authentication is done. Therefore,
163 <code>%{REMOTE_USER}</code> will not be set in this case.</p>
165 <p>The following variables provide the values of the named HTTP request
166 headers. The values of other headers can be obtained with the
167 <code>req</code> <a href="#functions">function</a>. Using these
168 variables may cause the header name to be added to the Vary
169 header of the HTTP response, except where otherwise noted for the
170 directive accepting the expression. The <code>req_novary</code>
171 <a href="#functions">function</a> may be used to circumvent this
174 <table border="1" style="zebra">
175 <columnspec><column width="1"/></columnspec>
177 <tr><th>Name</th></tr>
178 <tr><td><code>HTTP_ACCEPT</code></td></tr>
179 <tr><td><code>HTTP_COOKIE</code></td></tr>
180 <tr><td><code>HTTP_FORWARDED</code></td></tr>
181 <tr><td><code>HTTP_HOST</code></td></tr>
182 <tr><td><code>HTTP_PROXY_CONNECTION</code></td></tr>
183 <tr><td><code>HTTP_REFERER</code></td></tr>
184 <tr><td><code>HTTP_USER_AGENT</code></td></tr>
188 <p>Other request related variables</p>
190 <table border="1" style="zebra">
191 <columnspec><column width=".4"/><column width=".6"/></columnspec>
193 <tr><th>Name</th><th>Description</th></tr>
194 <tr><td><code>REQUEST_METHOD</code></td>
195 <td>The HTTP method of the incoming request (e.g.
196 <code>GET</code>)</td></tr>
197 <tr><td><code>REQUEST_SCHEME</code></td>
198 <td>The scheme part of the request's URI</td></tr>
199 <tr><td><code>REQUEST_URI</code></td>
200 <td>The path part of the request's URI</td></tr>
201 <tr><td><code>DOCUMENT_URI</code></td>
202 <td>Same as <code>REQUEST_URI</code></td></tr>
203 <tr><td><code>REQUEST_FILENAME</code></td>
204 <td>The full local filesystem path to the file or script matching the
205 request, if this has already been determined by the server at the
206 time <code>REQUEST_FILENAME</code> is referenced. Otherwise, such
207 as when used in virtual host context, the same value as
208 <code>REQUEST_URI</code> </td></tr>
209 <tr><td><code>SCRIPT_FILENAME</code></td>
210 <td>Same as <code>REQUEST_FILENAME</code></td></tr>
211 <tr><td><code>LAST_MODIFIED</code></td>
212 <td>The date and time of last modification of the file in the format
213 <code>20101231235959</code>, if this has already been determined by
214 the server at the time <code>LAST_MODIFIED</code> is referenced.
216 <tr><td><code>SCRIPT_USER</code></td>
217 <td>The user name of the owner of the script.</td></tr>
218 <tr><td><code>SCRIPT_GROUP</code></td>
219 <td>The group name of the group of the script.</td></tr>
220 <tr><td><code>PATH_INFO</code></td>
221 <td>The trailing path name information, see
222 <directive module="core">AcceptPathInfo</directive></td></tr>
223 <tr><td><code>QUERY_STRING</code></td>
224 <td>The query string of the current request</td></tr>
225 <tr><td><code>IS_SUBREQ</code></td>
226 <td>"<code>true</code>" if the current request is a subrequest,
227 "<code>false</code>" otherwise</td></tr>
228 <tr><td><code>THE_REQUEST</code></td>
229 <td>The complete request line (e.g.,
230 "<code>GET /index.html HTTP/1.1</code>")</td></tr>
231 <tr><td><code>REMOTE_ADDR</code></td>
232 <td>The IP address of the remote host</td></tr>
233 <tr><td><code>REMOTE_PORT</code></td>
234 <td>The port of the remote host (2.4.26 and later)</td></tr>
235 <tr><td><code>REMOTE_HOST</code></td>
236 <td>The host name of the remote host</td></tr>
237 <tr><td><code>REMOTE_USER</code></td>
238 <td>The name of the authenticated user, if any (not available during <directive><If></directive>)</td></tr>
239 <tr><td><code>REMOTE_IDENT</code></td>
240 <td>The user name set by <module>mod_ident</module></td></tr>
241 <tr><td><code>SERVER_NAME</code></td>
242 <td>The <directive module="core">ServerName</directive> of
243 the current vhost</td></tr>
244 <tr><td><code>SERVER_PORT</code></td>
245 <td>The server port of the current vhost, see
246 <directive module="core">ServerName</directive></td></tr>
247 <tr><td><code>SERVER_ADMIN</code></td>
248 <td>The <directive module="core">ServerAdmin</directive> of
249 the current vhost</td></tr>
250 <tr><td><code>SERVER_PROTOCOL</code></td>
251 <td>The protocol used by the request (e.g. HTTP/1.1). In some types of
252 internal subrequests, this variable has the value
253 <code>INCLUDED</code>.</td></tr>
254 <tr><td><code>SERVER_PROTOCOL_VERSION</code></td>
255 <td>A number that encodes the HTTP version of the request:
256 <code>1000 * major + minor</code>. For example, <code>1001</code>
257 corresponds to HTTP/1.1 and <code>9</code> corresponds
258 to HTTP/0.9</td></tr>
259 <tr><td><code>SERVER_PROTOCOL_VERSION_MAJOR</code></td>
260 <td>The major version part of the HTTP version of the request,
261 e.g. <code>1</code> for HTTP/1.0</td></tr>
262 <tr><td><code>SERVER_PROTOCOL_VERSION_MINOR</code></td>
263 <td>The minor version part of the HTTP version of the request,
264 e.g. <code>0</code> for HTTP/1.0</td></tr>
265 <tr><td><code>DOCUMENT_ROOT</code></td>
266 <td>The <directive module="core">DocumentRoot</directive> of
267 the current vhost</td></tr>
268 <tr><td><code>AUTH_TYPE</code></td>
269 <td>The configured <directive
270 module="mod_authn_core">AuthType</directive> (e.g.
271 "<code>basic</code>")</td></tr>
272 <tr><td><code>CONTENT_TYPE</code></td>
273 <td>The content type of the response (not available during <directive><If></directive>)</td></tr>
274 <tr><td><code>HANDLER</code></td>
275 <td>The name of the <a href="handler.html">handler</a> creating
276 the response</td></tr>
277 <tr><td><code>HTTP2</code></td>
278 <td>"<code>on</code>" if the request uses http/2,
279 "<code>off</code>" otherwise</td></tr>
280 <tr><td><code>HTTPS</code></td>
281 <td>"<code>on</code>" if the request uses https,
282 "<code>off</code>" otherwise</td></tr>
283 <tr><td><code>IPV6</code></td>
284 <td>"<code>on</code>" if the connection uses IPv6,
285 "<code>off</code>" otherwise</td></tr>
286 <tr><td><code>REQUEST_STATUS</code></td>
287 <td>The HTTP error status of the request (not available during <directive><If></directive>)</td></tr>
288 <tr><td><code>REQUEST_LOG_ID</code></td>
289 <td>The error log id of the request (see
290 <directive module="core">ErrorLogFormat</directive>)</td></tr>
291 <tr><td><code>CONN_LOG_ID</code></td>
292 <td>The error log id of the connection (see
293 <directive module="core">ErrorLogFormat</directive>)</td></tr>
294 <tr><td><code>CONN_REMOTE_ADDR</code></td>
295 <td>The peer IP address of the connection (see the
296 <module>mod_remoteip</module> module)</td></tr>
297 <tr><td><code>CONTEXT_PREFIX</code></td>
299 <tr><td><code>CONTEXT_DOCUMENT_ROOT</code></td>
304 <p>Misc variables</p>
306 <table border="1" style="zebra">
307 <columnspec><column width=".4"/><column width=".6"/></columnspec>
309 <tr><th>Name</th><th>Description</th></tr>
310 <tr><td><code>TIME_YEAR</code></td>
311 <td>The current year (e.g. <code>2010</code>)</td></tr>
312 <tr><td><code>TIME_MON</code></td>
313 <td>The current month (<code>01</code>, ..., <code>12</code>)</td></tr>
314 <tr><td><code>TIME_DAY</code></td>
315 <td>The current day of the month (<code>01</code>, ...)</td></tr>
316 <tr><td><code>TIME_HOUR</code></td>
317 <td>The hour part of the current time
318 (<code>00</code>, ..., <code>23</code>)</td></tr>
319 <tr><td><code>TIME_MIN</code></td>
320 <td>The minute part of the current time </td></tr>
321 <tr><td><code>TIME_SEC</code></td>
322 <td>The second part of the current time </td></tr>
323 <tr><td><code>TIME_WDAY</code></td>
324 <td>The day of the week (starting with <code>0</code>
325 for Sunday)</td></tr>
326 <tr><td><code>TIME</code></td>
327 <td>The date and time in the format
328 <code>20101231235959</code></td></tr>
329 <tr><td><code>SERVER_SOFTWARE</code></td>
330 <td>The server version string</td></tr>
331 <tr><td><code>API_VERSION</code></td>
332 <td>The date of the API version (module magic number)</td></tr>
335 <p>Some modules register additional variables, see e.g.
336 <module>mod_ssl</module>.</p>
341 <title>Binary operators</title>
343 <p>With the exception of some built-in comparison operators, binary
344 operators have the form "<code>-[a-zA-Z][a-zA-Z0-9_]+</code>", i.e. a
345 minus and at least two characters. The name is not case sensitive.
346 Modules may register additional binary operators.</p>
349 <title>Comparison operators</title>
351 <table border="1" style="zebra">
352 <columnspec><column width=".2"/><column width=".2"/><column width=".6"/></columnspec>
354 <tr><th>Name</th><th>Alternative</th> <th>Description</th></tr>
355 <tr><td><code>==</code></td>
356 <td><code>=</code></td>
357 <td>String equality</td></tr>
358 <tr><td><code>!=</code></td>
360 <td>String inequality</td></tr>
361 <tr><td><code><</code></td>
363 <td>String less than</td></tr>
364 <tr><td><code><=</code></td>
366 <td>String less than or equal</td></tr>
367 <tr><td><code>></code></td>
369 <td>String greater than</td></tr>
370 <tr><td><code>>=</code></td>
372 <td>String greater than or equal</td></tr>
373 <tr><td><code>=~</code></td>
375 <td>String matches the regular expression</td></tr>
376 <tr><td><code>!~</code></td>
378 <td>String does not match the regular expression</td></tr>
379 <tr><td><code>-eq</code></td>
380 <td><code>eq</code></td>
381 <td>Integer equality</td></tr>
382 <tr><td><code>-ne</code></td>
383 <td><code>ne</code></td>
384 <td>Integer inequality</td></tr>
385 <tr><td><code>-lt</code></td>
386 <td><code>lt</code></td>
387 <td>Integer less than</td></tr>
388 <tr><td><code>-le</code></td>
389 <td><code>le</code></td>
390 <td>Integer less than or equal</td></tr>
391 <tr><td><code>-gt</code></td>
392 <td><code>gt</code></td>
393 <td>Integer greater than</td></tr>
394 <tr><td><code>-ge</code></td>
395 <td><code>ge</code></td>
396 <td>Integer greater than or equal</td></tr>
400 <section id="binaryother">
401 <title>Other binary operators</title>
403 <table border="1" style="zebra">
404 <columnspec><column width=".2"/><column width=".8"/></columnspec>
406 <tr><th>Name</th><th>Description</th></tr>
407 <tr><td><code>-ipmatch</code></td>
408 <td>IP address matches address/netmask</td></tr>
409 <tr><td><code>-strmatch</code></td>
410 <td>left string matches pattern given by right string (containing
411 wildcards *, ?, [])</td></tr>
412 <tr><td><code>-strcmatch</code></td>
413 <td>same as <code>-strmatch</code>, but case insensitive</td></tr>
414 <tr><td><code>-fnmatch</code></td>
415 <td>same as <code>-strmatch</code>, but slashes are not matched by
423 <title>Unary operators</title>
425 <p>Unary operators take one argument and have the form
426 "<code>-[a-zA-Z]</code>", i.e. a minus and one character.
427 The name <em>is</em> case sensitive.
428 Modules may register additional unary operators.</p>
430 <table border="1" style="zebra">
431 <columnspec><column width=".2"/><column width=".2"/><column width=".6"/></columnspec>
433 <tr><th>Name</th><th>Description</th><th>Restricted</th></tr>
434 <tr><td><code>-d</code></td>
435 <td>The argument is treated as a filename.
436 True if the file exists and is a directory</td><td>yes</td></tr>
437 <tr><td><code>-e</code></td>
438 <td>The argument is treated as a filename.
439 True if the file (or dir or special) exists</td><td>yes</td></tr>
440 <tr><td><code>-f</code></td>
441 <td>The argument is treated as a filename.
442 True if the file exists and is regular file</td><td>yes</td></tr>
443 <tr><td><code>-s</code></td>
444 <td>The argument is treated as a filename.
445 True if the file exists and is not empty</td><td>yes</td></tr>
446 <tr><td><code>-L</code></td>
447 <td>The argument is treated as a filename.
448 True if the file exists and is symlink</td><td>yes</td></tr>
449 <tr><td><code>-h</code></td>
450 <td>The argument is treated as a filename.
451 True if the file exists and is symlink
452 (same as <code>-L</code>)</td><td>yes</td></tr>
453 <tr><td><code>-F</code></td>
454 <td>True if string is a valid file, accessible via all the server's
455 currently-configured access controls for that path. This uses an
456 internal subrequest to do the check, so use it with care - it can
457 impact your server's performance!</td><td></td></tr>
458 <tr><td><code>-U</code></td>
459 <td>True if string is a valid URL, accessible via all the server's
460 currently-configured access controls for that path. This uses an
461 internal subrequest to do the check, so use it with care - it can
462 impact your server's performance!</td><td></td></tr>
463 <tr><td><code>-A</code></td>
464 <td>Alias for <code>-U</code></td><td></td></tr>
465 <tr><td><code>-n</code></td>
466 <td>True if string is not empty</td><td></td></tr>
467 <tr><td><code>-z</code></td>
468 <td>True if string is empty</td><td></td></tr>
469 <tr><td><code>-T</code></td>
470 <td>False if string is empty, "<code>0</code>", "<code>off</code>",
471 "<code>false</code>", or "<code>no</code>" (case insensitive).
472 True otherwise.</td><td></td></tr>
473 <tr><td><code>-R</code></td>
474 <td>Same as "<code>%{REMOTE_ADDR} -ipmatch ...</code>", but more
479 <p>The operators marked as "restricted" are not available in some modules
480 like <module>mod_include</module>.</p>
483 <section id="functions">
484 <title>Functions</title>
486 <p>Normal string-valued functions take one string as argument and return
487 a string. Functions names are not case sensitive.
488 Modules may register additional functions.</p>
490 <table border="1" style="zebra">
491 <columnspec><column width=".2"/><column width=".4"/><column width=".4"/></columnspec>
493 <tr><th>Name</th><th>Description</th><th>Special notes</th></tr>
494 <tr><td><code>req</code>, <code>http</code></td>
495 <td>Get HTTP request header; header names may be added to the Vary
496 header, see below</td><td></td></tr>
497 <tr><td><code>req_novary</code></td>
498 <td>Same as <code>req</code>, but header names will not be added to the
499 Vary header</td><td></td></tr>
500 <tr><td><code>resp</code></td>
501 <td>Get HTTP response header (most response headers will not yet be set
502 during <directive><If></directive>)</td><td></td></tr>
503 <tr><td><code>reqenv</code></td>
504 <td>Lookup request environment variable (as a shortcut,
505 <code>v</code> can also be used to access variables).
507 <td>ordering</td></tr>
508 <tr><td><code>osenv</code></td>
509 <td>Lookup operating system environment variable</td><td></td></tr>
510 <tr><td><code>note</code></td>
511 <td>Lookup request note</td><td>ordering</td></tr>
512 <tr><td><code>env</code></td>
513 <td>Return first match of <code>note</code>, <code>reqenv</code>,
514 <code>osenv</code></td><td>ordering</td></tr>
515 <tr><td><code>tolower</code></td>
516 <td>Convert string to lower case</td><td></td></tr>
517 <tr><td><code>toupper</code></td>
518 <td>Convert string to upper case</td><td></td></tr>
519 <tr><td><code>escape</code></td>
520 <td>Escape special characters in %hex encoding</td><td></td></tr>
521 <tr><td><code>unescape</code></td>
522 <td>Unescape %hex encoded string, leaving encoded slashes alone;
523 return empty string if %00 is found</td><td></td></tr>
524 <tr><td><code>base64</code></td>
525 <td>Encode the string using base64 encoding</td><td></td></tr>
526 <tr><td><code>unbase64</code></td>
527 <td>Decode base64 encoded string, return truncated string if 0x00 is
528 found</td><td></td></tr>
529 <tr><td><code>md5</code></td>
530 <td>Hash the string using MD5, then encode the hash with hexadecimal
531 encoding</td><td></td></tr>
532 <tr><td><code>sha1</code></td>
533 <td>Hash the string using SHA1, then encode the hash with hexadecimal
534 encoding</td><td></td></tr>
535 <tr><td><code>file</code></td>
536 <td>Read contents from a file (including line endings, when present)
537 </td><td>restricted</td></tr>
538 <tr><td><code>filemod</code></td>
539 <td>Return last modification time of a file (or 0 if file does not exist
540 or is not regular file)</td><td>restricted</td></tr>
541 <tr><td><code>filesize</code></td>
542 <td>Return size of a file (or 0 if file does not exist or is not
543 regular file)</td><td>restricted</td></tr>
544 <tr><td><code>ldap</code></td>
545 <td>Escape characters as required by LDAP distinguished name escaping
546 (RFC4514) and LDAP filter escaping (RFC4515).</td><td></td></tr>
547 <tr><td><code>replace</code></td>
548 <td>replace(string, "from", "to") replaces all occurrences of "from"
549 in the string with "to".</td><td></td></tr>
553 <p>The functions marked as "restricted" in the final column are not
554 available in some modules like <module>mod_include</module>.</p>
556 <p>The functions marked as "ordering" in the final column require some
557 consideration for the ordering of different components of the server,
558 especially when the function is used within the
559 <<directive module="core">If</directive>> directive which is
560 evaluated relatively early.</p>
562 <title>Environment variable ordering</title>
563 When environment variables are looked up within an
564 <<directive module="core">If</directive>> condition, it's important
565 to consider how extremely early in request processing that this
566 resolution occurs. As a guideline, any directive defined outside of virtual host
567 context (directory, location, htaccess) is not likely to have yet had a
568 chance to execute. <directive module="mod_setenvif">SetEnvIf</directive>
569 in virtual host scope is one directive that runs prior to this resolution
572 When <code>reqenv</code> is used outside of <<directive module="core"
573 >If</directive>>, the resolution will generally occur later, but the
574 exact timing depends on the directive the expression has been used within.
577 <p>When the functions <code>req</code> or <code>http</code> are used,
578 the header name will automatically be added to the Vary header of the
579 HTTP response, except where otherwise noted for the directive accepting
580 the expression. The <code>req_novary</code> function can be used to
581 prevent names from being added to the Vary header.</p>
583 <p>In addition to string-valued functions, there are also
584 list-valued functions which take one string as argument and return a
585 wordlist, i.e. a list of strings. The wordlist can be used with the
586 special <code>-in</code> operator. Functions names are not case
587 sensitive. Modules may register additional functions.</p>
589 <p>There are no built-in list-valued functions. <module>mod_ssl</module>
590 provides <code>PeerExtList</code>. See the description of
591 <directive module="mod_ssl">SSLRequire</directive> for details
592 (but <code>PeerExtList</code> is also usable outside
593 of <directive module="mod_ssl">SSLRequire</directive>).</p>
597 <section id="examples">
599 <title>Example expressions</title>
600 <p>The following examples show how expressions might be used to
601 evaluate requests:</p>
603 <!-- This section should probably be extended with more, useful examples -->
604 <highlight language="config">
605 # Compare the host name to example.com and redirect to www.example.com if it matches
606 <If "%{HTTP_HOST} == 'example.com'">
607 Redirect permanent "/" "http://www.example.com/"
610 # Force text/plain if requesting a file with the query string contains 'forcetext'
611 <If "%{QUERY_STRING} =~ /forcetext/">
615 # Only allow access to this content during business hours
616 <Directory "/foo/bar/business">
617 Require expr %{TIME_HOUR} -gt 9 && %{TIME_HOUR} -lt 17
620 # Check a HTTP header for a list of values
621 <If "%{HTTP:X-example-header} in { 'foo', 'bar', 'baz' }">
622 Header set matched true
625 # Check an environment variable for a regular expression, negated.
626 <If "! reqenv('REDIRECT_FOO') =~ /bar/">
627 Header set matched true
630 # Check result of URI mapping by running in Directory context with -f
631 <Directory "/var/www">
632 AddEncoding x-gzip gz
633 <If "-f '%{REQUEST_FILENAME}.unzipme' && ! %{HTTP:Accept-Encoding} =~ /gzip/">
634 SetOutputFilter INFLATE
638 # Check against the client IP
639 <If "-R '192.168.1.0/24'">
640 Header set matched true
643 # Function examples in boolean context
644 <If "md5('foo') == 'acbd18db4cc2f85cedef654fccc4a4d8'">
645 Header set checksum-matched true
647 <If "md5('foo') == replace('md5:XXXd18db4cc2f85cedef654fccc4a4d8', 'md5:XXX', 'acb')">
648 Header set checksum-matched-2 true
651 # Function example in string context
652 Header set foo-checksum "expr=%{md5:foo}"
654 # This delays the evaluation of the condition clause compared to <If>
655 Header always set CustomHeader my-value "expr=%{REQUEST_URI} =~ m#^/special_path\.php$#"
663 <table border="1" style="zebra">
664 <columnspec><column width=".2"/><column width=".2"/><column width=".6"/></columnspec>
666 <tr><th>Name</th><th>Alternative</th> <th>Description</th></tr>
667 <tr><td><code>-in</code></td>
668 <td><code>in</code></td>
669 <td>string contained in wordlist</td></tr>
670 <tr><td><code>/regexp/</code></td>
671 <td><code>m#regexp#</code></td>
672 <td>Regular expression (the second form allows different
673 delimiters than /)</td></tr>
674 <tr><td><code>/regexp/i</code></td>
675 <td><code>m#regexp#i</code></td>
676 <td>Case insensitive regular expression</td></tr>
677 <tr><td><code>$0 ... $9</code></td>
679 <td>Regular expression backreferences</td></tr>
682 <section id="rebackref">
683 <title>Regular expression backreferences</title>
684 <p>The strings <code>$0</code> ... <code>$9</code> allow to reference
685 the capture groups from a previously executed, successfully
686 matching regular expressions. They can normally only be used in the
687 same expression as the matching regex, but some modules allow special
693 <section id="sslrequire">
694 <title>Comparison with SSLRequire</title>
695 <p>The <em>ap_expr</em> syntax is mostly a superset of the syntax of the
696 deprecated <directive module="mod_ssl">SSLRequire</directive> directive.
697 The differences are described in <directive
698 module="mod_ssl">SSLRequire</directive>'s documentation.</p>
701 <section id="compatibility">
702 <title>Version History</title>
703 <p>The <code>req_novary</code> <a href="#functions">function</a>
704 is available for versions 2.4.4 and later.</p>
705 <p>The <code>SERVER_PROTOCOL_VERSION</code>,
706 <code>SERVER_PROTOCOL_VERSION_MAJOR</code> and
707 <code>SERVER_PROTOCOL_VERSION_MINOR</code>
708 <a href="#vars">variables</a>
709 are available for versions 2.5.0 and later.</p>