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<title>Expressions in Apache HTTP Server</title>

<summary>

<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>

</summary>

<section id="grammar">

<title>Grammar in BNF notation</title>

<blockquote>

<pre>

expr ::= "<strong>true</strong>" | "<strong>false</strong>"

| "<strong>!</strong>" expr

| expr "<strong>&amp;&amp;</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>&lt;</strong>" word

| word "<strong>&lt;=</strong>" word

| word "<strong>&gt;</strong>" word

| word "<strong>&gt;=</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>

</section>

<section id="vars">

<title>Variables</title>

<p>The expression parser provides a number of variables of the form

<code>%{HTTP_HOST}</code>. Note that the value of a variable may depend

on the phase of the request processing in which it is evaluated. For

example, an expression used in an <directive>&lt;If &gt;</directive>

directive is evaluated before authentication is done. Therefore,

<code>%{REMOTE_USER}</code> will not be set in this case.</p>

<p>The following variables provide the values of the named HTTP request

headers. The values of other headers can be obtained witht the

<code>req</code> <a href="#functions">function</a>.</p>

<table border="1" style="zebra">

<columnspec><column width="1"/></columnspec>

<tr><th>Name</th></tr>

<tr><td><code>HTTP_ACCEPT</code></td></tr>

<tr><td><code>HTTP_FORWARDED</code></td></tr>

<tr><td><code>HTTP_HOST</code></td></tr>

<tr><td><code>HTTP_PROXY_CONNECTION</code></td></tr>

<tr><td><code>HTTP_REFERER</code></td></tr>

<tr><td><code>HTTP_USER_AGENT</code></td></tr>

</table>

<p>Other request related variables</p>

<table border="1" style="zebra">

<columnspec><column width=".4"/><column width=".6"/></columnspec>

<tr><th>Name</th><th>Description</th></tr>

<tr><td><code>REQUEST_METHOD</code></td>

<td>The HTTP method of the incoming request (e.g.

<code>GET</code>)</td></tr>

<tr><td><code>REQUEST_SCHEME</code></td>

<td>The scheme part of the request's URI</td></tr>

<tr><td><code>REQUEST_URI</code></td>

<td>The URI of the request</td></tr>

<tr><td><code>REQUEST_FILENAME</code></td>

<td></td></tr>

<tr><td><code>SCRIPT_FILENAME</code></td>

<td>Same as <code>REQUEST_FILENAME</code></td></tr>

<tr><td><code>SCRIPT_USER</code></td>

<td>The user name of the owner of the script.</td></tr>

<tr><td><code>SCRIPT_GROUP</code></td>

<td>The group name of the group of the script.</td></tr>

<tr><td><code>PATH_INFO</code></td>

<td></td></tr>

<tr><td><code>QUERY_STRING</code></td>

<td>The query string of the current request</td></tr>

<tr><td><code>IS_SUBREQ</code></td>

<td>"<code>true</code>" if the current request is a subrequest,

"<code>false</code>" otherwise</td></tr>

<tr><td><code>THE_REQUEST</code></td>

<td>The complete request line (e.g.,

"<code>GET /index.html HTTP/1.1</code>")</td></tr>

<tr><td><code>REMOTE_ADDR</code></td>

<td>The IP address of the remote host</td></tr>

<tr><td><code>REMOTE_HOST</code></td>

<td>The host name of the remote host</td></tr>

<tr><td><code>REMOTE_USER</code></td>

<td>The name of the authenticated user (if any)</td></tr>

<tr><td><code>REMOTE_IDENT</code></td>

<td>The user name set by <module>mod_ident</module></td></tr>

<tr><td><code>SERVER_NAME</code></td>

<td>The <directive module="core">ServerName</directive> of

the current vhost</td></tr>

<tr><td><code>SERVER_PORT</code></td>

<td>The server port of the current vhost, see

<directive module="core">ServerName</directive></td></tr>

<tr><td><code>SERVER_ADMIN</code></td>

<td>The <directive module="core">ServerAdmin</directive> of

the current vhost</td></tr>

<tr><td><code>SERVER_PROTOCOL</code></td>

<td>The protocol used by the request</td></tr>

<tr><td><code>DOCUMENT_ROOT</code></td>

<td>The <directive module="core">DocumentRoot</directive> of

the current vhost</td></tr>

<tr><td><code>AUTH_TYPE</code></td>

<td>The configured <directive module="mod_authn_core">AuthType</directive>

(e.g. "<code>basic</code>")</td></tr>

<tr><td><code>CONTENT_TYPE</code></td>

<td>The content type of the response</td></tr>

<tr><td><code>HANDLER</code></td>

<td>The name of the <a href="handler.html">handler</a> creating

the response</td></tr>

<tr><td><code>HTTPS</code></td>

<td>"<code>on</code>" if the request uses https,

"<code>off</code>" otherwise</td></tr>

<tr><td><code>IPV6</code></td>

<td>"<code>on</code>" if the connection uses IPv6,

"<code>off</code>" otherwise</td></tr>

<tr><td><code>REQUEST_LOG_ID</code></td>

<td>The error log id of the request (see

<directive module="core">ErrorLogFormat</directive>)</td></tr>

<tr><td><code>CONN_LOG_ID</code></td>

<td>The error log id of the connection (see

<directive module="core">ErrorLogFormat</directive>)</td></tr>

</table>

<p>Misc variables</p>

<table border="1" style="zebra">

<columnspec><column width=".4"/><column width=".6"/></columnspec>

<tr><th>Name</th><th>Description</th></tr>

<tr><td><code>TIME_YEAR</code></td>

<td>The current year (e.g. <code>2010</code>)</td></tr>

<tr><td><code>TIME_MON</code></td>

<td>The current month (<code>1</code>, ..., <code>12</code>)</td></tr>

<tr><td><code>TIME_DAY</code></td>

<td>The current day of the month</td></tr>

<tr><td><code>TIME_HOUR</code></td>

<td>The hour part of the current time

(<code>0</code>, ..., <code>23</code>)</td></tr>

<tr><td><code>TIME_MIN</code></td>

<td>The minute part of the current time </td></tr>

<tr><td><code>TIME_SEC</code></td>

<td>The second part of the current time </td></tr>

<tr><td><code>TIME_WDAY</code></td>

<td>The day of the week (starting with <code>0</code>

for Sunday)</td></tr>

<tr><td><code>TIME</code></td>

<td>The date and time in the format <code>20101231235959</code></td></tr>

<tr><td><code>SERVER_SOFTWARE</code></td>

<td>The server version string</td></tr>

<tr><td><code>API_VERSION</code></td>

<td>The date of the API version (module magic number)</td></tr>

</table>

<p>Some modules register additional variables, see e.g. <module>mod_ssl</module>.</p>

</section>

<section id="binop">

<title>Binary operators</title>

<p>With the exception of some built-in comparison operators, binary

operators have the form "<code>-[a-zA-Z][a-zA-Z0-9_]+</code>", i.e. a

minus and at least two characters. The name is not case sensitive.

Modules may register additional binary operators.</p>

<section id="comp">

<title>Comparison operators</title>

<table border="1" style="zebra">

<columnspec><column width=".2"/><column width=".2"/><column width=".6"/></columnspec>

<tr><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><td><code>!=</code></td>

<td></td>

<td>String inequality</td></tr>

<tr><td><code>&lt;</code></td>

<td></td>

<td>String less than</td></tr>

<tr><td><code>&lt;=</code></td>

<td></td>

<td>String less than or equal</td></tr>

<tr><td><code>&gt;</code></td>

<td></td>

<td>String greater than</td></tr>

<tr><td><code>&gt;=</code></td>

<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><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><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><td><code>-ge</code></td>

<td><code>ge</code></td>

<td>Integer greater than or equal</td></tr>

</table>

</section>

<section id="binaryother">

<title>Other binary operators</title>

<table border="1" style="zebra">

<columnspec><column width=".2"/><column width=".8"/></columnspec>

<tr><th>Name</th><th>Description</th></tr>

<tr><td><code>-ipmatch</code></td>

<td>IP address matches address/netmask</td></tr>

<tr><td><code>-strmatch</code></td>

<td>left string matches pattern given by right string (containing

wildcards *, ?, [])</td></tr>

<tr><td><code>-strcmatch</code></td>

<td>same as <code>-strmatch</code>, but case insensitive</td></tr>

<tr><td><code>-fnmatch</code></td>

<td>same as <code>-strmatch</code>, but slashes are not matched by

wildcards</td></tr>

</table>

</section>

</section>

<section id="unnop">

<title>Unary operators</title>

<p>Unary operators have the form "<code>-[a-zA-Z]</code>", i.e. a

minus and one character. The name <em>is</em> case sensitive.

Modules may register additional unary operators.</p>

<table border="1" style="zebra">

<columnspec><column width=".2"/><column width=".2"/><column width=".6"/></columnspec>

<tr><th>Name</th><th>Description</th></tr>

<tr><td><code>-n</code></td>

<td>True if string is not empty</td></tr>

<tr><td><code>-z</code></td>

<td>True if string is empty</td></tr>

<tr><td><code>-T</code></td>

<td>False if string is empty, "<code>0</code>", "<code>off</code>",

"<code>false</code>", or "<code>no</code>" (case insensitive).

True otherwise.</td></tr>

<tr><td><code>-R</code></td>

<td>Same as "<code>%{REMOTE_ADDR} -ipmatch ...</code>", but more efficient

</td></tr>

</table>

</section>

<section id="functions">

<title>Functions</title>

<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 border="1" style="zebra">

<columnspec><column width=".2"/><column width=".8"/></columnspec>

<tr><th>Name</th><th>Description</th></tr>

<tr><td><code>req</code>, <code>http</code></td>

<td>Get HTTP request header</td></tr>

<tr><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><td><code>osenv</code></td>

<td>Lookup operating system environment variable</td></tr>

<tr><td><code>note</code></td>

<td>Lookup request note</td></tr>

<tr><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><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><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. <module>mod_ssl</module>

provides <code>PeerExtList</code>. See the description of

<directive module="mod_ssl">SSLRequire</directive> for details

(but <code>PeerExtList</code> is also usable outside

of <directive module="mod_ssl">SSLRequire</directive>).</p>

</section>

<section id="other">

<title>Other</title>

<table border="1" style="zebra">

<columnspec><column width=".2"/><column width=".2"/><column width=".6"/></columnspec>

<tr><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><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><td><code>$0 ... $9</code></td>

<td></td>

<td>Regular expression backreferences</td></tr>

</table>

<section id="rebackref">

<title>Regular expression backreferences</title>

<p>The strings <code>$0</code> ... <code>$9</code> allow to reference

the capture groups from 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>

</section>

</section>

</manualpage>