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<manualpage metafile="expr.xml.meta">

  <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>
    <p>The <em>ap_expr</em> expression is intended to replace most other
        expression variants in HTTPD. For example, the deprecated
        <directive module="mod_ssl">SSLRequire</directive> expressions can be
        replaced by <a href="mod/mod_authz_core.html#reqexpr">Require expr</a>.
    </p>
  </summary>

<seealso><directive module="core" type="section">If</directive></seealso>
<seealso><directive module="core" type="section">ElseIf</directive></seealso>
<seealso><directive module="core" type="section">Else</directive></seealso>
<seealso><directive module="mod_auth_basic">AuthBasicFake</directive></seealso>
<seealso><directive module="mod_auth_form">AuthFormLoginRequiredLocation</directive></seealso>
<seealso><directive module="mod_auth_form">AuthFormLoginSuccessLocation</directive></seealso>
<seealso><directive module="mod_auth_form">AuthFormLogoutLocation</directive></seealso>
<seealso><directive module="mod_rewrite">RewriteCond</directive></seealso>
<seealso><directive module="mod_setenvif">SetEnvIfExpr</directive></seealso>
<seealso><directive module="mod_headers">Header</directive></seealso>
<seealso><directive module="mod_headers">RequestHeader</directive></seealso>
<seealso><directive module="mod_filter">FilterProvider</directive></seealso>
<seealso><a href="mod/mod_authz_core.html#reqexpr">Require expr</a></seealso>
<seealso><directive module="mod_ssl">SSLRequire</directive></seealso>
<seealso><directive module="mod_log_debug">LogMessage</directive></seealso>
<seealso><module>mod_include</module></seealso>

  <section id="grammar">
    <title>Grammar in Backus-Naur Form notation</title>
      <p><a href="http://en.wikipedia.org/wiki/Backus%E2%80%93Naur_Form">Backus-Naur Form</a> (BNF) is a notation
      technique for context-free grammars, often used to describe the syntax of languages used in computing.
      In most cases, expressions are used to express boolean values.
      For these, the starting point in the BNF is <code>expr</code>. However, a few directives
      like <directive module="mod_log_debug">LogMessage</directive> accept expressions
      that evaluate to a string value. For those, the starting point in the BNF is <code>string</code>.
      </p>
<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 with the
    <code>req</code> <a href="#functions">function</a>. Using these
    variables may cause the header name to be added to the Vary
    header of the HTTP response, except where otherwise noted for the
    directive accepting the expression. The <code>req_novary</code>
    <a href="#functions">function</a> may be used to circumvent this
    behavior.</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 path part of the request's URI</td></tr>
    <tr><td><code>DOCUMENT_URI</code></td>
        <td>Same as REQUEST_URI</td></tr>
    <tr><td><code>REQUEST_FILENAME</code></td>
        <td>The full local filesystem path to the file or script matching the
            request, if this has already been determined by the server at the
            time <code>REQUEST_FILENAME</code> is referenced. Otherwise, such
            as when used in virtual host context, the same value as
            <code>REQUEST_URI</code> </td></tr>
    <tr><td><code>SCRIPT_FILENAME</code></td>
        <td>Same as <code>REQUEST_FILENAME</code></td></tr>
    <tr><td><code>LAST_MODIFIED</code></td>
        <td>The date and time of last modification of the file in the format
            <code>20101231235959</code>, if this has already been determined by
            the server at the time <code>LAST_MODIFIED</code> is referenced.
            </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>The trailing path name information, see
            <directive module="core">AcceptPathInfo</directive></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_STATUS</code></td>
        <td>The HTTP error status of the request</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>
    <tr><td><code>CONN_REMOTE_ADDR</code></td>
        <td>The peer IP address of the connection (see the
            <module>mod_remoteip</module> module)</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 take one argument and 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><th>Restricted</th></tr>
    <tr><td><code>-d</code></td>
        <td>The argument is treated as a filename.
            True if the file exists and is a directory</td><td>yes</td></tr>
    <tr><td><code>-e</code></td>
        <td>The argument is treated as a filename.
            True if the file (or dir or special) exists</td><td>yes</td></tr>
    <tr><td><code>-f</code></td>
        <td>The argument is treated as a filename.
            True if the file exists and is regular file</td><td>yes</td></tr>
    <tr><td><code>-s</code></td>
        <td>The argument is treated as a filename.
            True if the file exists and is not empty</td><td>yes</td></tr>
    <tr><td><code>-L</code></td>
        <td>The argument is treated as a filename.
            True if the file exists and is symlink</td><td>yes</td></tr>
    <tr><td><code>-h</code></td>
        <td>The argument is treated as a filename.
            True if the file exists and is symlink
            (same as <code>-L</code>)</td><td>yes</td></tr>
    <tr><td><code>-F</code></td>
        <td>True if string is a valid file, accessible via all the server's
            currently-configured access controls for that path. This uses an
            internal subrequest to do the check, so use it with care - it can
            impact your server's performance!</td><td></td></tr>
    <tr><td><code>-U</code></td>
        <td>True if string is a valid URL, accessible via all the server's
            currently-configured access controls for that path. This uses an
            internal subrequest to do the check, so use it with care - it can
            impact your server's performance!</td><td></td></tr>
    <tr><td><code>-A</code></td>
        <td>Alias for <code>-U</code></td><td></td></tr>
    <tr><td><code>-n</code></td>
        <td>True if string is not empty</td><td></td></tr>
    <tr><td><code>-z</code></td>
        <td>True if string is empty</td><td></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><td></td></tr>
    <tr><td><code>-R</code></td>
        <td>Same as "<code>%{REMOTE_ADDR} -ipmatch ...</code>", but more efficient
        </td><td></td></tr>
    </table>

    <p>The operators marked as "restricted" are not available in some modules
    like <module>mod_include</module>.</p>
</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><th>Restricted</th></tr>
    <tr><td><code>req</code>, <code>http</code></td>
        <td>Get HTTP request header; header names may be added to the Vary
            header, see below</td><td></td></tr>
    <tr><td><code>req_novary</code></td>
        <td>Same as <code>req</code>, but header names will not be added to the
            Vary header</td><td></td></tr>
    <tr><td><code>resp</code></td>
        <td>Get HTTP response header</td><td></td></tr>
    <tr><td><code>reqenv</code></td>
        <td>Lookup request environment variable (as a shortcut, <code>v</code> can be used too to access variables).</td><td></td></tr>
    <tr><td><code>osenv</code></td>
        <td>Lookup operating system environment variable</td><td></td></tr>
    <tr><td><code>note</code></td>
        <td>Lookup request note</td><td></td></tr>
    <tr><td><code>env</code></td>
        <td>Return first match of <code>note</code>, <code>reqenv</code>,
            <code>osenv</code></td><td></td></tr>
    <tr><td><code>tolower</code></td>
        <td>Convert string to lower case</td><td></td></tr>
    <tr><td><code>toupper</code></td>
        <td>Convert string to upper case</td><td></td></tr>
    <tr><td><code>escape</code></td>
        <td>Escape special characters in %hex encoding</td><td></td></tr>
    <tr><td><code>unescape</code></td>
        <td>Unescape %hex encoded string, leaving encoded slashes alone;
            return empty string if %00 is found</td><td></td></tr>
    <tr><td><code>base64</code></td>
        <td>Encode the string using base64 encoding</td><td></td></tr>
    <tr><td><code>unbase64</code></td>
        <td>Decode base64 encoded string, return truncated string if 0x00 is
            found</td><td></td></tr>
    <tr><td><code>md5</code></td>
        <td>Hash the string using MD5, then encode the hash with hexadecimal
            encoding</td><td></td></tr>
    <tr><td><code>sha1</code></td>
        <td>Hash the string using SHA1, then encode the hash with hexadecimal
            encoding</td><td></td></tr>
    <tr><td><code>file</code></td>
        <td>Read contents from a file</td><td>yes</td></tr>
    <tr><td><code>filesize</code></td>
        <td>Return size of a file (or 0 if file does not exist or is not
            regular file)</td><td>yes</td></tr>

    </table>

    <p>The functions marked as "restricted" are not available in some modules
    like <module>mod_include</module>.</p>

    <p>When the functions <code>req</code> or <code>http</code> are used,
    the header name will automatically be added to the Vary header of the
    HTTP response, except where otherwise noted for the directive accepting
    the expression. The <code>req_novary</code> function can be used to
    prevent names from being added to the Vary header.</p>

    <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="examples">
    
	<title>Example expressions</title>
	<p>The following examples show how expressions might be used to evaluate requests:</p>
	<!-- This section should probably be extended with more, useful examples -->
	<highlight language="config">
# Compare the host name to example.com and redirect to www.example.com if it matches
&lt;If "%{HTTP_HOST} == 'example.com'"&gt;
    Redirect permanent / http://www.example.com/
&lt;/If&gt;

# Force text/plain if requesting a file with the query string contains 'forcetext'
&lt;If "%{QUERY_STRING} =~ /forcetext/"&gt;
    ForceType text/plain
&lt;/If&gt;

# Only allow access to this content during business hours
&lt;Directory "/foo/bar/business"&gt;
    Require expr "%{TIME_HOUR} -gt 9 &amp;&amp; %{TIME_HOUR} -lt 17"
&lt;/Directory&gt;	
	</highlight>
</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>

<section id="sslrequire">
    <title>Comparison with SSLRequire</title>
    <p>The <em>ap_expr</em> syntax is mostly a superset of the syntax of the
    deprecated <directive module="mod_ssl">SSLRequire</directive> directive.
    The differences are described in <directive
    module="mod_ssl">SSLRequire</directive>'s documentation.</p>
</section>

<section id="compatibility">
    <title>Version History</title>
    <p>The <code>req_novary</code> <a href="#functions">function</a>
    is available for versions 2.4.4 and later.</p>
</section>

</manualpage>
