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<title>Expressions in Apache HTTP Server - Apache HTTP Server</title>
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<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>
<p class="apache">Apache HTTP Server Version 2.3</p>
<div id="path">
<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="./">Version 2.3</a></div><div id="page-content"><div id="preamble"><h1>Expressions in Apache HTTP Server</h1>
<div class="toplang">
</div>
<p>Historically, there are several syntax variants for expressions used to express
a condition in the different modules of the Apache HTTP Server.
There is some ongoing effort to only use a single variant, called <em>ap_expr</em>,
for all configuration directives.
This document describes the <em>ap_expr</em> expression parser.
</p>
</div>
<div id="quickview"><ul id="toc"><li><img alt="" src="/images/down.gif" /> <a href="#grammar">Grammar in BNF notation</a></li>
</ul></div>
<div class="section">
<h2><a name="grammar" id="grammar">Grammar in BNF notation</a></h2>
<blockquote>
<pre>
expr ::= "<strong>true</strong>" | "<strong>false</strong>"
| "<strong>!</strong>" expr
| expr "<strong>&&</strong>" expr
| expr "<strong>||</strong>" expr
| "<strong>(</strong>" expr "<strong>)</strong>"
| comp
comp ::= stringcomp
| integercomp
| unaryop word
| word binaryop word
| word "<strong>in</strong>" "<strong>{</strong>" wordlist "<strong>}</strong>"
| word "<strong>in</strong>" listfunction
| word "<strong>=~</strong>" regex
| word "<strong>!~</strong>" regex
stringcomp ::= word "<strong>==</strong>" word
| word "<strong>!=</strong>" word
| word "<strong><</strong>" word
| word "<strong><=</strong>" word
| word "<strong>></strong>" word
| word "<strong>>=</strong>" word
integercomp ::= word "<strong>-eq</strong>" word | word "<strong>eq</strong>" word
| word "<strong>-ne</strong>" word | word "<strong>ne</strong>" word
| word "<strong>-lt</strong>" word | word "<strong>lt</strong>" word
| word "<strong>-le</strong>" word | word "<strong>le</strong>" word
| word "<strong>-gt</strong>" word | word "<strong>gt</strong>" word
| word "<strong>-ge</strong>" word | word "<strong>ge</strong>" word
wordlist ::= word
| wordlist "<strong>,</strong>" word
word ::= word "<strong>.</strong>" word
| digit
| "<strong>'</strong>" string "<strong>'</strong>"
| "<strong>"</strong>" string "<strong>"</strong>"
| variable
| rebackref
| function
string ::= stringpart
| string stringpart
stringpart ::= cstring
| variable
| rebackref
cstring ::= ...
digit ::= [0-9]+
variable ::= "<strong>%{</strong>" varname "<strong>}</strong>"
| "<strong>%{</strong>" funcname "<strong>:</strong>" funcargs "<strong>}</strong>"
rebackref ::= "<strong>$</strong>" [0-9]
function ::= funcname "<strong>(</strong>" word "<strong>)</strong>"
listfunction ::= listfuncname "<strong>(</strong>" word "<strong>)</strong>"
</pre>
</blockquote>
<div class="section">
<h2><a name="vars" id="vars">Variables</a></h2>
<p>XXX: not all vars are available in all request phases</p>
<p>Request headers (XXX:see req function)</p>
<table class="bordered"><tr class="header"><th>Name</th></tr>
<tr><td><code>HTTP_ACCEPT</code></td></tr>
<tr class="odd"><td><code>HTTP_FORWARDED</code></td></tr>
<tr><td><code>HTTP_HOST</code></td></tr>
<tr class="odd"><td><code>HTTP_PROXY_CONNECTION</code></td></tr>
<tr><td><code>HTTP_REFERER</code></td></tr>
<tr class="odd"><td><code>HTTP_USER_AGENT</code></td></tr>
</table>
<p>Other request related variables</p>
<table class="bordered"><tr class="header"><th>Name</th><th>Description</th></tr>
<tr><td><code>REQUEST_METHOD</code></td>
<td /></tr>
<tr class="odd"><td><code>REQUEST_SCHEME</code></td>
<td /></tr>
<tr><td><code>REQUEST_URI</code></td>
<td /></tr>
<tr class="odd"><td><code>REQUEST_FILENAME</code></td>
<td /></tr>
<tr><td><code>REMOTE_HOST</code></td>
<td /></tr>
<tr class="odd"><td><code>REMOTE_IDENT</code></td>
<td /></tr>
<tr><td><code>REMOTE_USER</code></td>
<td /></tr>
<tr class="odd"><td><code>SERVER_ADMIN</code></td>
<td /></tr>
<tr><td><code>SERVER_NAME</code></td>
<td /></tr>
<tr class="odd"><td><code>SERVER_PORT</code></td>
<td /></tr>
<tr><td><code>SERVER_PROTOCOL</code></td>
<td /></tr>
<tr class="odd"><td><code>SCRIPT_FILENAME</code></td>
<td /></tr>
<tr><td><code>PATH_INFO</code></td>
<td /></tr>
<tr class="odd"><td><code>QUERY_STRING</code></td>
<td /></tr>
<tr><td><code>IS_SUBREQ</code></td>
<td /></tr>
<tr class="odd"><td><code>DOCUMENT_ROOT</code></td>
<td /></tr>
<tr><td><code>AUTH_TYPE</code></td>
<td /></tr>
<tr class="odd"><td><code>THE_REQUEST</code></td>
<td /></tr>
<tr><td><code>CONTENT_TYPE</code></td>
<td /></tr>
<tr class="odd"><td><code>HANDLER</code></td>
<td /></tr>
<tr><td><code>REMOTE_ADDR</code></td>
<td /></tr>
<tr class="odd"><td><code>HTTPS</code></td>
<td /></tr>
<tr><td><code>IPV6</code></td>
<td /></tr>
<tr class="odd"><td><code>REQUEST_LOG_ID</code></td>
<td /></tr>
<tr><td><code>CONN_LOG_ID</code></td>
<td /></tr>
</table>
<p>Misc variables</p>
<table class="bordered"><tr class="header"><th>Name</th><th>Description</th></tr>
<tr><td><code>TIME_YEAR</code></td>
<td /></tr>
<tr class="odd"><td><code>TIME_MON</code></td>
<td /></tr>
<tr><td><code>TIME_DAY</code></td>
<td /></tr>
<tr class="odd"><td><code>TIME_HOUR</code></td>
<td /></tr>
<tr><td><code>TIME_MIN</code></td>
<td /></tr>
<tr class="odd"><td><code>TIME_SEC</code></td>
<td /></tr>
<tr><td><code>TIME_WDAY</code></td>
<td /></tr>
<tr class="odd"><td><code>TIME</code></td>
<td /></tr>
<tr><td><code>SERVER_SOFTWARE</code></td>
<td /></tr>
<tr class="odd"><td><code>API_VERSION</code></td>
<td /></tr>
</table>
<div class="section">
<h2><a name="binop" id="binop">Binary operators</a></h2>
<p>With the exception of some built-in comparison operators, binary
minus and at least two characters. The name is not case sensitive.
Modules may register additional binary operators.</p>
<table class="bordered"><tr class="header"><th>Name</th><th>Alternative</th> <th>Description</th></tr>
<tr><td><code>==</code></td>
<td><code>=</code></td>
<td>String equality</td></tr>
<tr class="odd"><td><code>!=</code></td>
<td />
<td>String inequality</td></tr>
<tr><td><code><</code></td>
<td />
<td>String less than</td></tr>
<tr class="odd"><td><code><=</code></td>
<td />
<td>String less than or equal</td></tr>
<tr><td><code>></code></td>
<td />
<td>String greater than</td></tr>
<tr class="odd"><td><code>>=</code></td>
<td />
<td>String greater than or equal</td></tr>
<tr><td><code>-eq</code></td>
<td><code>eq</code></td>
<td>Integer equality</td></tr>
<tr class="odd"><td><code>-ne</code></td>
<td><code>ne</code></td>
<td>Integer inequality</td></tr>
<tr><td><code>-lt</code></td>
<td><code>lt</code></td>
<td>Integer less than</td></tr>
<tr class="odd"><td><code>-le</code></td>
<td><code>le</code></td>
<td>Integer less than or equal</td></tr>
<tr><td><code>-gt</code></td>
<td><code>gt</code></td>
<td>Integer greater than</td></tr>
<tr class="odd"><td><code>-ge</code></td>
<td><code>ge</code></td>
<td>Integer greater than or equal</td></tr>
</table>
<div class="section">
<h2><a name="unnop" id="unnop">Unary operators</a></h2>
minus and one character. The name <em>is</em> case sensitive.
Modules may register additional unary operators.</p>
<table class="bordered"><tr class="header"><th>Name</th><th>Description</th></tr>
<tr><td><code>-n</code></td>
<td>String is not empty</td></tr>
<tr class="odd"><td><code>-z</code></td>
<td>String is empty</td></tr>
</table>
<div class="section">
<h2><a name="functions" id="functions">Functions</a></h2>
<p>Normal string-valued functions take one string as argument and return
a string. Functions names are not case sensitive.
Modules may register additional functions.</p>
<table class="bordered"><tr class="header"><th>Name</th><th>Description</th></tr>
<tr><td><code>req</code>, <code>http</code></td>
<td>Get HTTP request header</td></tr>
<tr class="odd"><td><code>resp</code></td>
<td>Get HTTP response header</td></tr>
<tr><td><code>reqenv</code></td>
<td>Lookup request environment variable</td></tr>
<tr class="odd"><td><code>osenv</code></td>
<td>Lookup operating system environment variable</td></tr>
<tr><td><code>note</code></td>
<td>Lookup request environment variable</td></tr>
<tr class="odd"><td><code>env</code></td>
<td>Return first match of <code>note</code>, <code>reqenv</code>,
<code>osenv</code></td></tr>
<tr><td><code>tolower</code></td>
<td>Convert string to lower case</td></tr>
<tr class="odd"><td><code>toupper</code></td>
<td>Convert string to uppser case</td></tr>
<tr><td><code>escape</code></td>
<td>Escape special characters in %hex encoding</td></tr>
<tr class="odd"><td><code>unescape</code></td>
<td>Unescape %hex encoded string, leaving URL-special characters encoded (XXX: describe better)</td></tr>
<tr><td><code>file</code></td>
<td>Read contents from a file</td></tr>
</table>
<p>In addition to string-valued functions, there are also list-valued functions which
take one string as argument and return a wordlist, i.e. a list of strings. The wordlist
can be used with the special <code>-in</code> operator.
Functions names are not case sensitive.
Modules may register additional functions.</p>
<p>There are no built-in list-valued functions. <code class="module"><a href="/mod/mod_ssl.html">mod_ssl</a></code>
provides <code>PeerExtList</code>. See the description of
(but <code>PeerExtList</code> is also usable outside
<div class="section">
<h2><a name="other" id="other">Other</a></h2>
<table class="bordered"><tr class="header"><th>Name</th><th>Alternative</th> <th>Description</th></tr>
<tr><td><code>-in</code></td>
<td><code>in</code></td>
<td>string contained in string list</td></tr>
<tr class="odd"><td><code>/regexp/</code></td>
<td><code>m#regexp#</code></td>
<td>Regular expression (the second form allows different delimiters than /)</td></tr>
<tr><td><code>/regexp/i</code></td>
<td><code>m#regexp#i</code></td>
<td>Case insensitive regular expression</td></tr>
<tr class="odd"><td><code>$0 ... $9</code></td>
<td />
<td>Regular expression backreferences</td></tr>
</table>
<h3><a name="rebackref" id="rebackref">Regular expression backreferences</a></h3>
<p>The strings <code>$0</code> ... <code>$9</code> allow to reference
the capture groups form a previously executed, successfully
matching regular expressions. They can normally only be used in the
same expression as the matching regex, but some modules allow special
uses.</p>
</div></div>
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