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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_rewrite">RewriteCond</directive></seealso>
52 <seealso><directive module="mod_setenvif">SetEnvIfExpr</directive></seealso>
53 <seealso><directive module="mod_headers">Header</directive></seealso>
54 <seealso><directive module="mod_headers">RequestHeader</directive></seealso>
55 <seealso><directive module="mod_filter">FilterProvider</directive></seealso>
56 <seealso><a href="mod/mod_authz_core.html#reqexpr">Require expr</a></seealso>
57 <seealso><a href="mod/mod_authnz_ldap.html#requser">Require ldap-user</a></seealso>
58 <seealso><a href="mod/mod_authnz_ldap.html#reqgroup">Require ldap-group</a></seealso>
59 <seealso><a href="mod/mod_authnz_ldap.html#reqdn">Require ldap-dn</a></seealso>
60 <seealso><a href="mod/mod_authnz_ldap.html#reqattribute">Require ldap-attribute</a></seealso>
61 <seealso><a href="mod/mod_authnz_ldap.html#reqfilter">Require ldap-filter</a></seealso>
62 <seealso><a href="mod/mod_authz_dbd.html#reqgroup">Require dbd-group</a></seealso>
63 <seealso><a href="mod/mod_authz_dbm.html#reqgroup">Require dbm-group</a></seealso>
64 <seealso><a href="mod/mod_authz_groupfile.html#reqgroup">Require group</a></seealso>
65 <seealso><a href="mod/mod_authz_host.html#reqhost">Require host</a></seealso>
66 <seealso><directive module="mod_ssl">SSLRequire</directive></seealso>
67 <seealso><directive module="mod_log_debug">LogMessage</directive></seealso>
68 <seealso><module>mod_include</module></seealso>
70 <section id="grammar">
71 <title>Grammar in Backus-Naur Form notation</title>
73 href="http://en.wikipedia.org/wiki/Backus%E2%80%93Naur_Form">Backus-Naur
74 Form</a> (BNF) is a notation technique for context-free grammars,
75 often used to describe the syntax of languages used in computing.
76 In most cases, expressions are used to express boolean values.
77 For these, the starting point in the BNF is <code>expr</code>.
78 However, a few directives like <directive
79 module="mod_log_debug">LogMessage</directive> accept expressions
80 that evaluate to a string value. For those, the starting point in
81 the BNF is <code>string</code>.
85 expr ::= "<strong>true</strong>" | "<strong>false</strong>"
86 | "<strong>!</strong>" expr
87 | expr "<strong>&&</strong>" expr
88 | expr "<strong>||</strong>" expr
89 | "<strong>(</strong>" expr "<strong>)</strong>"
96 | word "<strong>in</strong>" "<strong>{</strong>" wordlist "<strong>}</strong>"
97 | word "<strong>in</strong>" listfunction
98 | word "<strong>=~</strong>" regex
99 | word "<strong>!~</strong>" regex
102 stringcomp ::= word "<strong>==</strong>" word
103 | word "<strong>!=</strong>" word
104 | word "<strong><</strong>" word
105 | word "<strong><=</strong>" word
106 | word "<strong>></strong>" word
107 | word "<strong>>=</strong>" word
109 integercomp ::= word "<strong>-eq</strong>" word | word "<strong>eq</strong>" word
110 | word "<strong>-ne</strong>" word | word "<strong>ne</strong>" word
111 | word "<strong>-lt</strong>" word | word "<strong>lt</strong>" word
112 | word "<strong>-le</strong>" word | word "<strong>le</strong>" word
113 | word "<strong>-gt</strong>" word | word "<strong>gt</strong>" word
114 | word "<strong>-ge</strong>" word | word "<strong>ge</strong>" word
117 | wordlist "<strong>,</strong>" word
119 word ::= word "<strong>.</strong>" word
121 | "<strong>'</strong>" string "<strong>'</strong>"
122 | "<strong>"</strong>" string "<strong>"</strong>"
127 string ::= stringpart
130 stringpart ::= cstring
137 variable ::= "<strong>%{</strong>" varname "<strong>}</strong>"
138 | "<strong>%{</strong>" funcname "<strong>:</strong>" funcargs "<strong>}</strong>"
140 rebackref ::= "<strong>$</strong>" [0-9]
142 function ::= funcname "<strong>(</strong>" word "<strong>)</strong>"
144 listfunction ::= listfuncname "<strong>(</strong>" word "<strong>)</strong>"
151 <title>Variables</title>
153 <p>The expression parser provides a number of variables of the form
154 <code>%{HTTP_HOST}</code>. Note that the value of a variable may depend
155 on the phase of the request processing in which it is evaluated. For
156 example, an expression used in an <directive><If ></directive>
157 directive is evaluated before authentication is done. Therefore,
158 <code>%{REMOTE_USER}</code> will not be set in this case.</p>
160 <p>The following variables provide the values of the named HTTP request
161 headers. The values of other headers can be obtained with the
162 <code>req</code> <a href="#functions">function</a>. Using these
163 variables may cause the header name to be added to the Vary
164 header of the HTTP response, except where otherwise noted for the
165 directive accepting the expression. The <code>req_novary</code>
166 <a href="#functions">function</a> may be used to circumvent this
169 <table border="1" style="zebra">
170 <columnspec><column width="1"/></columnspec>
172 <tr><th>Name</th></tr>
173 <tr><td><code>HTTP_ACCEPT</code></td></tr>
174 <tr><td><code>HTTP_COOKIE</code></td></tr>
175 <tr><td><code>HTTP_FORWARDED</code></td></tr>
176 <tr><td><code>HTTP_HOST</code></td></tr>
177 <tr><td><code>HTTP_PROXY_CONNECTION</code></td></tr>
178 <tr><td><code>HTTP_REFERER</code></td></tr>
179 <tr><td><code>HTTP_USER_AGENT</code></td></tr>
183 <p>Other request related variables</p>
185 <table border="1" style="zebra">
186 <columnspec><column width=".4"/><column width=".6"/></columnspec>
188 <tr><th>Name</th><th>Description</th></tr>
189 <tr><td><code>REQUEST_METHOD</code></td>
190 <td>The HTTP method of the incoming request (e.g.
191 <code>GET</code>)</td></tr>
192 <tr><td><code>REQUEST_SCHEME</code></td>
193 <td>The scheme part of the request's URI</td></tr>
194 <tr><td><code>REQUEST_URI</code></td>
195 <td>The path part of the request's URI</td></tr>
196 <tr><td><code>DOCUMENT_URI</code></td>
197 <td>Same as <code>REQUEST_URI</code></td></tr>
198 <tr><td><code>REQUEST_FILENAME</code></td>
199 <td>The full local filesystem path to the file or script matching the
200 request, if this has already been determined by the server at the
201 time <code>REQUEST_FILENAME</code> is referenced. Otherwise, such
202 as when used in virtual host context, the same value as
203 <code>REQUEST_URI</code> </td></tr>
204 <tr><td><code>SCRIPT_FILENAME</code></td>
205 <td>Same as <code>REQUEST_FILENAME</code></td></tr>
206 <tr><td><code>LAST_MODIFIED</code></td>
207 <td>The date and time of last modification of the file in the format
208 <code>20101231235959</code>, if this has already been determined by
209 the server at the time <code>LAST_MODIFIED</code> is referenced.
211 <tr><td><code>SCRIPT_USER</code></td>
212 <td>The user name of the owner of the script.</td></tr>
213 <tr><td><code>SCRIPT_GROUP</code></td>
214 <td>The group name of the group of the script.</td></tr>
215 <tr><td><code>PATH_INFO</code></td>
216 <td>The trailing path name information, see
217 <directive module="core">AcceptPathInfo</directive></td></tr>
218 <tr><td><code>QUERY_STRING</code></td>
219 <td>The query string of the current request</td></tr>
220 <tr><td><code>IS_SUBREQ</code></td>
221 <td>"<code>true</code>" if the current request is a subrequest,
222 "<code>false</code>" otherwise</td></tr>
223 <tr><td><code>THE_REQUEST</code></td>
224 <td>The complete request line (e.g.,
225 "<code>GET /index.html HTTP/1.1</code>")</td></tr>
226 <tr><td><code>REMOTE_ADDR</code></td>
227 <td>The IP address of the remote host</td></tr>
228 <tr><td><code>REMOTE_HOST</code></td>
229 <td>The host name of the remote host</td></tr>
230 <tr><td><code>REMOTE_USER</code></td>
231 <td>The name of the authenticated user, if any (not available during <directive><If ></directive>)</td></tr>
232 <tr><td><code>REMOTE_IDENT</code></td>
233 <td>The user name set by <module>mod_ident</module></td></tr>
234 <tr><td><code>SERVER_NAME</code></td>
235 <td>The <directive module="core">ServerName</directive> of
236 the current vhost</td></tr>
237 <tr><td><code>SERVER_PORT</code></td>
238 <td>The server port of the current vhost, see
239 <directive module="core">ServerName</directive></td></tr>
240 <tr><td><code>SERVER_ADMIN</code></td>
241 <td>The <directive module="core">ServerAdmin</directive> of
242 the current vhost</td></tr>
243 <tr><td><code>SERVER_PROTOCOL</code></td>
244 <td>The protocol used by the request</td></tr>
245 <tr><td><code>DOCUMENT_ROOT</code></td>
246 <td>The <directive module="core">DocumentRoot</directive> of
247 the current vhost</td></tr>
248 <tr><td><code>AUTH_TYPE</code></td>
249 <td>The configured <directive
250 module="mod_authn_core">AuthType</directive> (e.g.
251 "<code>basic</code>")</td></tr>
252 <tr><td><code>CONTENT_TYPE</code></td>
253 <td>The content type of the response (not available during <directive><If ></directive>)</td></tr>
254 <tr><td><code>HANDLER</code></td>
255 <td>The name of the <a href="handler.html">handler</a> creating
256 the response</td></tr>
257 <tr><td><code>HTTP2</code></td>
258 <td>"<code>on</code>" if the request uses http/2,
259 "<code>off</code>" otherwise</td></tr>
260 <tr><td><code>HTTPS</code></td>
261 <td>"<code>on</code>" if the request uses https,
262 "<code>off</code>" otherwise</td></tr>
263 <tr><td><code>IPV6</code></td>
264 <td>"<code>on</code>" if the connection uses IPv6,
265 "<code>off</code>" otherwise</td></tr>
266 <tr><td><code>REQUEST_STATUS</code></td>
267 <td>The HTTP error status of the request (not available during <directive><If ></directive>)</td></tr>
268 <tr><td><code>REQUEST_LOG_ID</code></td>
269 <td>The error log id of the request (see
270 <directive module="core">ErrorLogFormat</directive>)</td></tr>
271 <tr><td><code>CONN_LOG_ID</code></td>
272 <td>The error log id of the connection (see
273 <directive module="core">ErrorLogFormat</directive>)</td></tr>
274 <tr><td><code>CONN_REMOTE_ADDR</code></td>
275 <td>The peer IP address of the connection (see the
276 <module>mod_remoteip</module> module)</td></tr>
277 <tr><td><code>CONTEXT_PREFIX</code></td>
279 <tr><td><code>CONTEXT_DOCUMENT_ROOT</code></td>
284 <p>Misc variables</p>
286 <table border="1" style="zebra">
287 <columnspec><column width=".4"/><column width=".6"/></columnspec>
289 <tr><th>Name</th><th>Description</th></tr>
290 <tr><td><code>TIME_YEAR</code></td>
291 <td>The current year (e.g. <code>2010</code>)</td></tr>
292 <tr><td><code>TIME_MON</code></td>
293 <td>The current month (<code>1</code>, ..., <code>12</code>)</td></tr>
294 <tr><td><code>TIME_DAY</code></td>
295 <td>The current day of the month</td></tr>
296 <tr><td><code>TIME_HOUR</code></td>
297 <td>The hour part of the current time
298 (<code>0</code>, ..., <code>23</code>)</td></tr>
299 <tr><td><code>TIME_MIN</code></td>
300 <td>The minute part of the current time </td></tr>
301 <tr><td><code>TIME_SEC</code></td>
302 <td>The second part of the current time </td></tr>
303 <tr><td><code>TIME_WDAY</code></td>
304 <td>The day of the week (starting with <code>0</code>
305 for Sunday)</td></tr>
306 <tr><td><code>TIME</code></td>
307 <td>The date and time in the format
308 <code>20101231235959</code></td></tr>
309 <tr><td><code>SERVER_SOFTWARE</code></td>
310 <td>The server version string</td></tr>
311 <tr><td><code>API_VERSION</code></td>
312 <td>The date of the API version (module magic number)</td></tr>
315 <p>Some modules register additional variables, see e.g.
316 <module>mod_ssl</module>.</p>
321 <title>Binary operators</title>
323 <p>With the exception of some built-in comparison operators, binary
324 operators have the form "<code>-[a-zA-Z][a-zA-Z0-9_]+</code>", i.e. a
325 minus and at least two characters. The name is not case sensitive.
326 Modules may register additional binary operators.</p>
329 <title>Comparison operators</title>
331 <table border="1" style="zebra">
332 <columnspec><column width=".2"/><column width=".2"/><column width=".6"/></columnspec>
334 <tr><th>Name</th><th>Alternative</th> <th>Description</th></tr>
335 <tr><td><code>==</code></td>
336 <td><code>=</code></td>
337 <td>String equality</td></tr>
338 <tr><td><code>!=</code></td>
340 <td>String inequality</td></tr>
341 <tr><td><code><</code></td>
343 <td>String less than</td></tr>
344 <tr><td><code><=</code></td>
346 <td>String less than or equal</td></tr>
347 <tr><td><code>></code></td>
349 <td>String greater than</td></tr>
350 <tr><td><code>>=</code></td>
352 <td>String greater than or equal</td></tr>
353 <tr><td><code>-eq</code></td>
354 <td><code>eq</code></td>
355 <td>Integer equality</td></tr>
356 <tr><td><code>-ne</code></td>
357 <td><code>ne</code></td>
358 <td>Integer inequality</td></tr>
359 <tr><td><code>-lt</code></td>
360 <td><code>lt</code></td>
361 <td>Integer less than</td></tr>
362 <tr><td><code>-le</code></td>
363 <td><code>le</code></td>
364 <td>Integer less than or equal</td></tr>
365 <tr><td><code>-gt</code></td>
366 <td><code>gt</code></td>
367 <td>Integer greater than</td></tr>
368 <tr><td><code>-ge</code></td>
369 <td><code>ge</code></td>
370 <td>Integer greater than or equal</td></tr>
374 <section id="binaryother">
375 <title>Other binary operators</title>
377 <table border="1" style="zebra">
378 <columnspec><column width=".2"/><column width=".8"/></columnspec>
380 <tr><th>Name</th><th>Description</th></tr>
381 <tr><td><code>-ipmatch</code></td>
382 <td>IP address matches address/netmask</td></tr>
383 <tr><td><code>-strmatch</code></td>
384 <td>left string matches pattern given by right string (containing
385 wildcards *, ?, [])</td></tr>
386 <tr><td><code>-strcmatch</code></td>
387 <td>same as <code>-strmatch</code>, but case insensitive</td></tr>
388 <tr><td><code>-fnmatch</code></td>
389 <td>same as <code>-strmatch</code>, but slashes are not matched by
397 <title>Unary operators</title>
399 <p>Unary operators take one argument and have the form
400 "<code>-[a-zA-Z]</code>", i.e. a minus and one character.
401 The name <em>is</em> case sensitive.
402 Modules may register additional unary operators.</p>
404 <table border="1" style="zebra">
405 <columnspec><column width=".2"/><column width=".2"/><column width=".6"/></columnspec>
407 <tr><th>Name</th><th>Description</th><th>Restricted</th></tr>
408 <tr><td><code>-d</code></td>
409 <td>The argument is treated as a filename.
410 True if the file exists and is a directory</td><td>yes</td></tr>
411 <tr><td><code>-e</code></td>
412 <td>The argument is treated as a filename.
413 True if the file (or dir or special) exists</td><td>yes</td></tr>
414 <tr><td><code>-f</code></td>
415 <td>The argument is treated as a filename.
416 True if the file exists and is regular file</td><td>yes</td></tr>
417 <tr><td><code>-s</code></td>
418 <td>The argument is treated as a filename.
419 True if the file exists and is not empty</td><td>yes</td></tr>
420 <tr><td><code>-L</code></td>
421 <td>The argument is treated as a filename.
422 True if the file exists and is symlink</td><td>yes</td></tr>
423 <tr><td><code>-h</code></td>
424 <td>The argument is treated as a filename.
425 True if the file exists and is symlink
426 (same as <code>-L</code>)</td><td>yes</td></tr>
427 <tr><td><code>-F</code></td>
428 <td>True if string is a valid file, accessible via all the server's
429 currently-configured access controls for that path. This uses an
430 internal subrequest to do the check, so use it with care - it can
431 impact your server's performance!</td><td></td></tr>
432 <tr><td><code>-U</code></td>
433 <td>True if string is a valid URL, accessible via all the server's
434 currently-configured access controls for that path. This uses an
435 internal subrequest to do the check, so use it with care - it can
436 impact your server's performance!</td><td></td></tr>
437 <tr><td><code>-A</code></td>
438 <td>Alias for <code>-U</code></td><td></td></tr>
439 <tr><td><code>-n</code></td>
440 <td>True if string is not empty</td><td></td></tr>
441 <tr><td><code>-z</code></td>
442 <td>True if string is empty</td><td></td></tr>
443 <tr><td><code>-T</code></td>
444 <td>False if string is empty, "<code>0</code>", "<code>off</code>",
445 "<code>false</code>", or "<code>no</code>" (case insensitive).
446 True otherwise.</td><td></td></tr>
447 <tr><td><code>-R</code></td>
448 <td>Same as "<code>%{REMOTE_ADDR} -ipmatch ...</code>", but more
453 <p>The operators marked as "restricted" are not available in some modules
454 like <module>mod_include</module>.</p>
457 <section id="functions">
458 <title>Functions</title>
460 <p>Normal string-valued functions take one string as argument and return
461 a string. Functions names are not case sensitive.
462 Modules may register additional functions.</p>
464 <table border="1" style="zebra">
465 <columnspec><column width=".2"/><column width=".4"/><column width=".4"/></columnspec>
467 <tr><th>Name</th><th>Description</th><th>Restricted</th></tr>
468 <tr><td><code>req</code>, <code>http</code></td>
469 <td>Get HTTP request header; header names may be added to the Vary
470 header, see below</td><td></td></tr>
471 <tr><td><code>req_novary</code></td>
472 <td>Same as <code>req</code>, but header names will not be added to the
473 Vary header</td><td></td></tr>
474 <tr><td><code>resp</code></td>
475 <td>Get HTTP response header</td><td></td></tr>
476 <tr><td><code>reqenv</code></td>
477 <td>Lookup request environment variable (as a shortcut,
478 <code>v</code> can be used too to access
479 variables).</td><td></td></tr>
480 <tr><td><code>osenv</code></td>
481 <td>Lookup operating system environment variable</td><td></td></tr>
482 <tr><td><code>note</code></td>
483 <td>Lookup request note</td><td></td></tr>
484 <tr><td><code>env</code></td>
485 <td>Return first match of <code>note</code>, <code>reqenv</code>,
486 <code>osenv</code></td><td></td></tr>
487 <tr><td><code>tolower</code></td>
488 <td>Convert string to lower case</td><td></td></tr>
489 <tr><td><code>toupper</code></td>
490 <td>Convert string to upper case</td><td></td></tr>
491 <tr><td><code>escape</code></td>
492 <td>Escape special characters in %hex encoding</td><td></td></tr>
493 <tr><td><code>unescape</code></td>
494 <td>Unescape %hex encoded string, leaving encoded slashes alone;
495 return empty string if %00 is found</td><td></td></tr>
496 <tr><td><code>base64</code></td>
497 <td>Encode the string using base64 encoding</td><td></td></tr>
498 <tr><td><code>unbase64</code></td>
499 <td>Decode base64 encoded string, return truncated string if 0x00 is
500 found</td><td></td></tr>
501 <tr><td><code>md5</code></td>
502 <td>Hash the string using MD5, then encode the hash with hexadecimal
503 encoding</td><td></td></tr>
504 <tr><td><code>sha1</code></td>
505 <td>Hash the string using SHA1, then encode the hash with hexadecimal
506 encoding</td><td></td></tr>
507 <tr><td><code>file</code></td>
508 <td>Read contents from a file (including line endings, when present)
509 </td><td>yes</td></tr>
510 <tr><td><code>filesize</code></td>
511 <td>Return size of a file (or 0 if file does not exist or is not
512 regular file)</td><td>yes</td></tr>
516 <p>The functions marked as "restricted" are not available in some modules
517 like <module>mod_include</module>.</p>
519 <p>When the functions <code>req</code> or <code>http</code> are used,
520 the header name will automatically be added to the Vary header of the
521 HTTP response, except where otherwise noted for the directive accepting
522 the expression. The <code>req_novary</code> function can be used to
523 prevent names from being added to the Vary header.</p>
525 <p>In addition to string-valued functions, there are also
526 list-valued functions which take one string as argument and return a
527 wordlist, i.e. a list of strings. The wordlist can be used with the
528 special <code>-in</code> operator. Functions names are not case
529 sensitive. Modules may register additional functions.</p>
531 <p>There are no built-in list-valued functions. <module>mod_ssl</module>
532 provides <code>PeerExtList</code>. See the description of
533 <directive module="mod_ssl">SSLRequire</directive> for details
534 (but <code>PeerExtList</code> is also usable outside
535 of <directive module="mod_ssl">SSLRequire</directive>).</p>
539 <section id="examples">
541 <title>Example expressions</title>
542 <p>The following examples show how expressions might be used to
543 evaluate requests:</p>
544 <!-- This section should probably be extended with more, useful examples -->
545 <highlight language="config">
546 # Compare the host name to example.com and redirect to www.example.com if it matches
547 <If "%{HTTP_HOST} == 'example.com'">
548 Redirect permanent "/" "http://www.example.com/"
551 # Force text/plain if requesting a file with the query string contains 'forcetext'
552 <If "%{QUERY_STRING} =~ /forcetext/">
556 # Only allow access to this content during business hours
557 <Directory "/foo/bar/business">
558 Require expr %{TIME_HOUR} -gt 9 && %{TIME_HOUR} -lt 17
561 # Check a HTTP header for a list of values
562 <If "%{HTTP:X-example-header} in { 'foo', 'bar', 'baz' }">
563 Header set matched true
566 # Check an environment variable for a regular expression, negated.
567 <If "! reqenv('REDIRECT_FOO') =~ /bar/">
568 Header set matched true
571 # Check result of URI mapping by running in Directory context with -f
572 <Directory "/var/www">
573 AddEncoding x-gzip gz
574 <If "-f '%{REQUEST_FILENAME}.unzipme' && ! %{HTTP:Accept-Encoding} =~ /gzip/">
575 SetOutputFilter INFLATE
579 # Function examples in boolean context
580 <If "md5('foo') == 'acbd18db4cc2f85cedef654fccc4a4d8'">
581 Header set checksum-matched true
583 <If "md5('foo') == replace('md5:XXXd18db4cc2f85cedef654fccc4a4d8', 'md5:XXX', 'acb')">
584 Header set checksum-matched-2 true
587 # Function example in string context
588 Header set foo-checksum "expr=%{md5:foo}"
590 # This delays the evaluation of the condition clause compared to <If>
591 Header always set CustomHeader my-value "expr=%{REQUEST_URI} =~ m#^/special_path.php$#"
599 <table border="1" style="zebra">
600 <columnspec><column width=".2"/><column width=".2"/><column width=".6"/></columnspec>
602 <tr><th>Name</th><th>Alternative</th> <th>Description</th></tr>
603 <tr><td><code>-in</code></td>
604 <td><code>in</code></td>
605 <td>string contained in wordlist</td></tr>
606 <tr><td><code>/regexp/</code></td>
607 <td><code>m#regexp#</code></td>
608 <td>Regular expression (the second form allows different
609 delimiters than /)</td></tr>
610 <tr><td><code>/regexp/i</code></td>
611 <td><code>m#regexp#i</code></td>
612 <td>Case insensitive regular expression</td></tr>
613 <tr><td><code>$0 ... $9</code></td>
615 <td>Regular expression backreferences</td></tr>
618 <section id="rebackref">
619 <title>Regular expression backreferences</title>
620 <p>The strings <code>$0</code> ... <code>$9</code> allow to reference
621 the capture groups from a previously executed, successfully
622 matching regular expressions. They can normally only be used in the
623 same expression as the matching regex, but some modules allow special
629 <section id="sslrequire">
630 <title>Comparison with SSLRequire</title>
631 <p>The <em>ap_expr</em> syntax is mostly a superset of the syntax of the
632 deprecated <directive module="mod_ssl">SSLRequire</directive> directive.
633 The differences are described in <directive
634 module="mod_ssl">SSLRequire</directive>'s documentation.</p>
637 <section id="compatibility">
638 <title>Version History</title>
639 <p>The <code>req_novary</code> <a href="#functions">function</a>
640 is available for versions 2.4.4 and later.</p>