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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.
36 <seealso><directive module="core">If</directive></seealso>
37 <seealso><module>mod_rewrite</module></seealso>
38 <seealso><module>mod_include</module></seealso>
39 <seealso><module>mod_setenvif</module></seealso>
40 <seealso><directive module="mod_ssl">SSLRequire</directive></seealso>
41 <seealso><directive module="mod_filter">FilterProvider</directive></seealso>
43 <section id="grammar">
44 <title>Grammar in Backus–Naur Form notation</title>
45 <p><a href="http://en.wikipedia.org/wiki/Backus%E2%80%93Naur_Form">Backus–Naur Form</a> (BNF) is a notation
46 technique for context-free grammars, often used to describe the syntax of languages used in computing.
50 expr ::= "<strong>true</strong>" | "<strong>false</strong>"
51 | "<strong>!</strong>" expr
52 | expr "<strong>&&</strong>" expr
53 | expr "<strong>||</strong>" expr
54 | "<strong>(</strong>" expr "<strong>)</strong>"
61 | word "<strong>in</strong>" "<strong>{</strong>" wordlist "<strong>}</strong>"
62 | word "<strong>in</strong>" listfunction
63 | word "<strong>=~</strong>" regex
64 | word "<strong>!~</strong>" regex
67 stringcomp ::= word "<strong>==</strong>" word
68 | word "<strong>!=</strong>" word
69 | word "<strong><</strong>" word
70 | word "<strong><=</strong>" word
71 | word "<strong>></strong>" word
72 | word "<strong>>=</strong>" word
74 integercomp ::= word "<strong>-eq</strong>" word | word "<strong>eq</strong>" word
75 | word "<strong>-ne</strong>" word | word "<strong>ne</strong>" word
76 | word "<strong>-lt</strong>" word | word "<strong>lt</strong>" word
77 | word "<strong>-le</strong>" word | word "<strong>le</strong>" word
78 | word "<strong>-gt</strong>" word | word "<strong>gt</strong>" word
79 | word "<strong>-ge</strong>" word | word "<strong>ge</strong>" word
82 | wordlist "<strong>,</strong>" word
84 word ::= word "<strong>.</strong>" word
86 | "<strong>'</strong>" string "<strong>'</strong>"
87 | "<strong>"</strong>" string "<strong>"</strong>"
95 stringpart ::= cstring
102 variable ::= "<strong>%{</strong>" varname "<strong>}</strong>"
103 | "<strong>%{</strong>" funcname "<strong>:</strong>" funcargs "<strong>}</strong>"
105 rebackref ::= "<strong>$</strong>" [0-9]
107 function ::= funcname "<strong>(</strong>" word "<strong>)</strong>"
109 listfunction ::= listfuncname "<strong>(</strong>" word "<strong>)</strong>"
116 <title>Variables</title>
118 <p>The expression parser provides a number of variables of the form
119 <code>%{HTTP_HOST}</code>. Note that the value of a variable may depend
120 on the phase of the request processing in which it is evaluated. For
121 example, an expression used in an <directive><If ></directive>
122 directive is evaluated before authentication is done. Therefore,
123 <code>%{REMOTE_USER}</code> will not be set in this case.</p>
125 <p>The following variables provide the values of the named HTTP request
126 headers. The values of other headers can be obtained witht the
127 <code>req</code> <a href="#functions">function</a>.</p>
129 <table border="1" style="zebra">
130 <columnspec><column width="1"/></columnspec>
132 <tr><th>Name</th></tr>
133 <tr><td><code>HTTP_ACCEPT</code></td></tr>
134 <tr><td><code>HTTP_FORWARDED</code></td></tr>
135 <tr><td><code>HTTP_HOST</code></td></tr>
136 <tr><td><code>HTTP_PROXY_CONNECTION</code></td></tr>
137 <tr><td><code>HTTP_REFERER</code></td></tr>
138 <tr><td><code>HTTP_USER_AGENT</code></td></tr>
142 <p>Other request related variables</p>
144 <table border="1" style="zebra">
145 <columnspec><column width=".4"/><column width=".6"/></columnspec>
147 <tr><th>Name</th><th>Description</th></tr>
148 <tr><td><code>REQUEST_METHOD</code></td>
149 <td>The HTTP method of the incoming request (e.g.
150 <code>GET</code>)</td></tr>
151 <tr><td><code>REQUEST_SCHEME</code></td>
152 <td>The scheme part of the request's URI</td></tr>
153 <tr><td><code>REQUEST_URI</code></td>
154 <td>The URI of the request</td></tr>
155 <tr><td><code>REQUEST_FILENAME</code></td>
157 <tr><td><code>SCRIPT_FILENAME</code></td>
158 <td>Same as <code>REQUEST_FILENAME</code></td></tr>
159 <tr><td><code>SCRIPT_USER</code></td>
160 <td>The user name of the owner of the script.</td></tr>
161 <tr><td><code>SCRIPT_GROUP</code></td>
162 <td>The group name of the group of the script.</td></tr>
163 <tr><td><code>PATH_INFO</code></td>
165 <tr><td><code>QUERY_STRING</code></td>
166 <td>The query string of the current request</td></tr>
167 <tr><td><code>IS_SUBREQ</code></td>
168 <td>"<code>true</code>" if the current request is a subrequest,
169 "<code>false</code>" otherwise</td></tr>
170 <tr><td><code>THE_REQUEST</code></td>
171 <td>The complete request line (e.g.,
172 "<code>GET /index.html HTTP/1.1</code>")</td></tr>
173 <tr><td><code>REMOTE_ADDR</code></td>
174 <td>The IP address of the remote host</td></tr>
175 <tr><td><code>REMOTE_HOST</code></td>
176 <td>The host name of the remote host</td></tr>
177 <tr><td><code>REMOTE_USER</code></td>
178 <td>The name of the authenticated user (if any)</td></tr>
179 <tr><td><code>REMOTE_IDENT</code></td>
180 <td>The user name set by <module>mod_ident</module></td></tr>
181 <tr><td><code>SERVER_NAME</code></td>
182 <td>The <directive module="core">ServerName</directive> of
183 the current vhost</td></tr>
184 <tr><td><code>SERVER_PORT</code></td>
185 <td>The server port of the current vhost, see
186 <directive module="core">ServerName</directive></td></tr>
187 <tr><td><code>SERVER_ADMIN</code></td>
188 <td>The <directive module="core">ServerAdmin</directive> of
189 the current vhost</td></tr>
190 <tr><td><code>SERVER_PROTOCOL</code></td>
191 <td>The protocol used by the request</td></tr>
192 <tr><td><code>DOCUMENT_ROOT</code></td>
193 <td>The <directive module="core">DocumentRoot</directive> of
194 the current vhost</td></tr>
195 <tr><td><code>AUTH_TYPE</code></td>
196 <td>The configured <directive module="mod_authn_core">AuthType</directive>
197 (e.g. "<code>basic</code>")</td></tr>
198 <tr><td><code>CONTENT_TYPE</code></td>
199 <td>The content type of the response</td></tr>
200 <tr><td><code>HANDLER</code></td>
201 <td>The name of the <a href="handler.html">handler</a> creating
202 the response</td></tr>
203 <tr><td><code>HTTPS</code></td>
204 <td>"<code>on</code>" if the request uses https,
205 "<code>off</code>" otherwise</td></tr>
206 <tr><td><code>IPV6</code></td>
207 <td>"<code>on</code>" if the connection uses IPv6,
208 "<code>off</code>" otherwise</td></tr>
209 <tr><td><code>REQUEST_LOG_ID</code></td>
210 <td>The error log id of the request (see
211 <directive module="core">ErrorLogFormat</directive>)</td></tr>
212 <tr><td><code>CONN_LOG_ID</code></td>
213 <td>The error log id of the connection (see
214 <directive module="core">ErrorLogFormat</directive>)</td></tr>
218 <p>Misc variables</p>
220 <table border="1" style="zebra">
221 <columnspec><column width=".4"/><column width=".6"/></columnspec>
223 <tr><th>Name</th><th>Description</th></tr>
224 <tr><td><code>TIME_YEAR</code></td>
225 <td>The current year (e.g. <code>2010</code>)</td></tr>
226 <tr><td><code>TIME_MON</code></td>
227 <td>The current month (<code>1</code>, ..., <code>12</code>)</td></tr>
228 <tr><td><code>TIME_DAY</code></td>
229 <td>The current day of the month</td></tr>
230 <tr><td><code>TIME_HOUR</code></td>
231 <td>The hour part of the current time
232 (<code>0</code>, ..., <code>23</code>)</td></tr>
233 <tr><td><code>TIME_MIN</code></td>
234 <td>The minute part of the current time </td></tr>
235 <tr><td><code>TIME_SEC</code></td>
236 <td>The second part of the current time </td></tr>
237 <tr><td><code>TIME_WDAY</code></td>
238 <td>The day of the week (starting with <code>0</code>
239 for Sunday)</td></tr>
240 <tr><td><code>TIME</code></td>
241 <td>The date and time in the format <code>20101231235959</code></td></tr>
242 <tr><td><code>SERVER_SOFTWARE</code></td>
243 <td>The server version string</td></tr>
244 <tr><td><code>API_VERSION</code></td>
245 <td>The date of the API version (module magic number)</td></tr>
248 <p>Some modules register additional variables, see e.g. <module>mod_ssl</module>.</p>
253 <title>Binary operators</title>
255 <p>With the exception of some built-in comparison operators, binary
256 operators have the form "<code>-[a-zA-Z][a-zA-Z0-9_]+</code>", i.e. a
257 minus and at least two characters. The name is not case sensitive.
258 Modules may register additional binary operators.</p>
261 <title>Comparison operators</title>
263 <table border="1" style="zebra">
264 <columnspec><column width=".2"/><column width=".2"/><column width=".6"/></columnspec>
266 <tr><th>Name</th><th>Alternative</th> <th>Description</th></tr>
267 <tr><td><code>==</code></td>
268 <td><code>=</code></td>
269 <td>String equality</td></tr>
270 <tr><td><code>!=</code></td>
272 <td>String inequality</td></tr>
273 <tr><td><code><</code></td>
275 <td>String less than</td></tr>
276 <tr><td><code><=</code></td>
278 <td>String less than or equal</td></tr>
279 <tr><td><code>></code></td>
281 <td>String greater than</td></tr>
282 <tr><td><code>>=</code></td>
284 <td>String greater than or equal</td></tr>
285 <tr><td><code>-eq</code></td>
286 <td><code>eq</code></td>
287 <td>Integer equality</td></tr>
288 <tr><td><code>-ne</code></td>
289 <td><code>ne</code></td>
290 <td>Integer inequality</td></tr>
291 <tr><td><code>-lt</code></td>
292 <td><code>lt</code></td>
293 <td>Integer less than</td></tr>
294 <tr><td><code>-le</code></td>
295 <td><code>le</code></td>
296 <td>Integer less than or equal</td></tr>
297 <tr><td><code>-gt</code></td>
298 <td><code>gt</code></td>
299 <td>Integer greater than</td></tr>
300 <tr><td><code>-ge</code></td>
301 <td><code>ge</code></td>
302 <td>Integer greater than or equal</td></tr>
306 <section id="binaryother">
307 <title>Other binary operators</title>
309 <table border="1" style="zebra">
310 <columnspec><column width=".2"/><column width=".8"/></columnspec>
312 <tr><th>Name</th><th>Description</th></tr>
313 <tr><td><code>-ipmatch</code></td>
314 <td>IP address matches address/netmask</td></tr>
315 <tr><td><code>-strmatch</code></td>
316 <td>left string matches pattern given by right string (containing
317 wildcards *, ?, [])</td></tr>
318 <tr><td><code>-strcmatch</code></td>
319 <td>same as <code>-strmatch</code>, but case insensitive</td></tr>
320 <tr><td><code>-fnmatch</code></td>
321 <td>same as <code>-strmatch</code>, but slashes are not matched by
329 <title>Unary operators</title>
331 <p>Unary operators have the form "<code>-[a-zA-Z]</code>", i.e. a
332 minus and one character. The name <em>is</em> case sensitive.
333 Modules may register additional unary operators.</p>
335 <table border="1" style="zebra">
336 <columnspec><column width=".2"/><column width=".2"/><column width=".6"/></columnspec>
338 <tr><th>Name</th><th>Description</th></tr>
339 <tr><td><code>-n</code></td>
340 <td>True if string is not empty</td></tr>
341 <tr><td><code>-z</code></td>
342 <td>True if string is empty</td></tr>
343 <tr><td><code>-T</code></td>
344 <td>False if string is empty, "<code>0</code>", "<code>off</code>",
345 "<code>false</code>", or "<code>no</code>" (case insensitive).
346 True otherwise.</td></tr>
347 <tr><td><code>-R</code></td>
348 <td>Same as "<code>%{REMOTE_ADDR} -ipmatch ...</code>", but more efficient
354 <section id="functions">
355 <title>Functions</title>
357 <p>Normal string-valued functions take one string as argument and return
358 a string. Functions names are not case sensitive.
359 Modules may register additional functions.</p>
361 <table border="1" style="zebra">
362 <columnspec><column width=".2"/><column width=".8"/></columnspec>
364 <tr><th>Name</th><th>Description</th></tr>
365 <tr><td><code>req</code>, <code>http</code></td>
366 <td>Get HTTP request header</td></tr>
367 <tr><td><code>resp</code></td>
368 <td>Get HTTP response header</td></tr>
369 <tr><td><code>reqenv</code></td>
370 <td>Lookup request environment variable</td></tr>
371 <tr><td><code>osenv</code></td>
372 <td>Lookup operating system environment variable</td></tr>
373 <tr><td><code>note</code></td>
374 <td>Lookup request note</td></tr>
375 <tr><td><code>env</code></td>
376 <td>Return first match of <code>note</code>, <code>reqenv</code>,
377 <code>osenv</code></td></tr>
378 <tr><td><code>tolower</code></td>
379 <td>Convert string to lower case</td></tr>
380 <tr><td><code>toupper</code></td>
381 <td>Convert string to uppser case</td></tr>
382 <tr><td><code>escape</code></td>
383 <td>Escape special characters in %hex encoding</td></tr>
384 <tr><td><code>unescape</code></td>
385 <td>Unescape %hex encoded string, leaving URL-special characters encoded (XXX: describe better)</td></tr>
386 <tr><td><code>file</code></td>
387 <td>Read contents from a file</td></tr>
390 <p>In addition to string-valued functions, there are also list-valued functions which
391 take one string as argument and return a wordlist, i.e. a list of strings. The wordlist
392 can be used with the special <code>-in</code> operator.
393 Functions names are not case sensitive.
394 Modules may register additional functions.</p>
396 <p>There are no built-in list-valued functions. <module>mod_ssl</module>
397 provides <code>PeerExtList</code>. See the description of
398 <directive module="mod_ssl">SSLRequire</directive> for details
399 (but <code>PeerExtList</code> is also usable outside
400 of <directive module="mod_ssl">SSLRequire</directive>).</p>
407 <table border="1" style="zebra">
408 <columnspec><column width=".2"/><column width=".2"/><column width=".6"/></columnspec>
410 <tr><th>Name</th><th>Alternative</th> <th>Description</th></tr>
411 <tr><td><code>-in</code></td>
412 <td><code>in</code></td>
413 <td>string contained in string list</td></tr>
414 <tr><td><code>/regexp/</code></td>
415 <td><code>m#regexp#</code></td>
416 <td>Regular expression (the second form allows different delimiters than /)</td></tr>
417 <tr><td><code>/regexp/i</code></td>
418 <td><code>m#regexp#i</code></td>
419 <td>Case insensitive regular expression</td></tr>
420 <tr><td><code>$0 ... $9</code></td>
422 <td>Regular expression backreferences</td></tr>
425 <section id="rebackref">
426 <title>Regular expression backreferences</title>
427 <p>The strings <code>$0</code> ... <code>$9</code> allow to reference
428 the capture groups from a previously executed, successfully
429 matching regular expressions. They can normally only be used in the
430 same expression as the matching regex, but some modules allow special