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<a href="http://www.apache.org/">Apache</a> &gt; <a href="http://httpd.apache.org/">HTTP Server</a> &gt; <a href="http://httpd.apache.org/docs/">Documentation</a> &gt; <a href="./">Version 2.4</a></div><div id="page-content"><div id="preamble"><h1>Expressions in Apache HTTP Server</h1>

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    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><th>Restricted</th></tr>

    <table class="bordered"><tr class="header"><th>Name</th><th>Description</th><th>Special notes</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 /></tr>

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

<tr class="odd"><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 /></tr>

        <code>v</code> can also be used to access variables).</td>

        <td>ordering</td></tr>

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

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

<tr class="odd"><td><code>note</code></td>

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

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

<tr><td><code>env</code></td>

        <td>Return first match of <code>note</code>, <code>reqenv</code>,

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

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

<tr class="odd"><td><code>tolower</code></td>

        <td>Convert string to lower case</td><td /></tr>

<tr><td><code>toupper</code></td>

            encoding</td><td /></tr>

<tr class="odd"><td><code>file</code></td>

        <td>Read contents from a file (including line endings, when present)

        </td><td>yes</td></tr>

<tr><td><code>filesize</code></td>

        </td><td>restricted</td></tr>

<tr><td><code>filemod</code></td>

        <td>Return last modification time of a file (or 0 if file does not exist

            or is not regular file)</td><td>restricted</td></tr>

<tr class="odd"><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>

            regular file)</td><td>restricted</td></tr>

</table>

    <p>The functions marked as "restricted" are not available in some modules

    like <code class="module"><a href="./mod/mod_include.html">mod_include</a></code>.</p>

    <p>The functions marked as "restricted" in the final column are not 

    available in some modules like <code class="module"><a href="./mod/mod_include.html">mod_include</a></code>.</p>

    <p>The functions marked as "ordering" in the final column require some

    consideration for the ordering of different components of the server,

    especially when the function is used within the 

    &lt;<code class="directive"><a href="./mod/core.html#if">If</a></code>&gt; directive which is

    evaluated relatively early.</p>

    <div class="note">

    <h3>Environment variable ordering</h3>

    When environment variables are looked up within an 

    &lt;<code class="directive"><a href="./mod/core.html#if">If</a></code>&gt; condition, it's important 

    to consider how extremely early in request processing that this 

    resolution occurs. As a guideline, any directive defined outside of virtual host 

    context (directory, location, htaccess) is not likely to have yet had a 

    chance to execute. <code class="directive"><a href="./mod/mod_setenvif.html#setenvif">SetEnvIf</a></code>

    in virtual host scope is one directive that runs prior to this resolution

    <br />

    <br />

    When <code>reqenv</code> is used outside of &lt;<code class="directive"><a href="./mod/core.html#if">If</a></code>&gt;, the resolution will generally occur later, but the 

    exact timing depends on the directive the expression has been used within.

    </div>

    <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

    is available for versions 2.4.4 and later.</p>

</div></div>

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