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<div id="preamble"><h1>Apache Module mod_include</h1>
<div class="toplang">
<p><span>Available Languages: </span><a href="../en/mod/mod_include.html" title="English">&nbsp;en&nbsp;</a> |
<a href="../ja/mod/mod_include.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a></p>
</div>
<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Server-parsed html documents (Server Side Includes)</td></tr>
<tr><th><a href="module-dict.html#Status">Status:</a></th><td>Base</td></tr>
<tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>include_module</td></tr>
<tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_include.c</td></tr>
<tr><th><a href="module-dict.html#Compatibility">Compatibility:</a></th><td>Implemented as an output filter since Apache
2.0</td></tr></table>
<h3>Summary</h3>

    <p>This module provides a filter which will process files
    before they are sent to the client. The processing is
    controlled by specially formatted SGML comments, referred to as
    <dfn>elements</dfn>. These elements allow conditional text, the
    inclusion of other files or programs, as well as the setting and
    printing of environment variables.</p>
</div>
<div id="quickview"><h3 class="directives">Directives</h3>
<ul id="toc">
<li><img alt="" src="../images/down.gif" /> <a href="#ssiendtag">SSIEndTag</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#ssierrormsg">SSIErrorMsg</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#ssistarttag">SSIStartTag</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#ssitimeformat">SSITimeFormat</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#ssiundefinedecho">SSIUndefinedEcho</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#xbithack">XBitHack</a></li>
</ul>
<h3>Topics</h3>
<ul id="topics">
<li><img alt="" src="../images/down.gif" /> <a href="#enabling">Enabling Server-Side Includes</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#pathinfo">PATH_INFO with Server Side Includes</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#elements">Basic Elements</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#includevars">Include Variables</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#substitution">Variable Substitution</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#flowctrl">Flow Control Elements</a></li>
</ul><h3>See also</h3>
<ul class="seealso">
<li><code class="directive"><a href="../mod/core.html#options">Options</a></code></li>
<li><code class="directive"><a href="../mod/core.html#acceptpathinfo">AcceptPathInfo</a></code></li>
<li><a href="../filter.html">Filters</a></li>
<li><a href="../howto/ssi.html">SSI Tutorial</a></li>
</ul></div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="enabling" id="enabling">Enabling Server-Side Includes</a></h2>
    

    <p>Server Side Includes are implemented by the
    <code>INCLUDES</code> <a href="../filter.html">filter</a>. If
    documents containing server-side include directives are given
    the extension .shtml, the following directives will make Apache
    parse them and assign the resulting document the mime type of
    <code>text/html</code>:</p>

    <div class="example"><p><code>
      AddType text/html .shtml<br />
      AddOutputFilter INCLUDES .shtml
    </code></p></div>

    <p>The following directive must be given for the directories
    containing the shtml files (typically in a
    <code class="directive"><a href="../mod/core.html#directory">&lt;Directory&gt;</a></code> section,
    but this directive is also valid in <code>.htaccess</code> files if
    <code class="directive"><a href="../mod/core.html#allowoverride">AllowOverride</a></code> <code>Options</code>
    is set):</p>

    <div class="example"><p><code>
      Options +Includes
    </code></p></div>

    <p>For backwards compatibility, the <code>server-parsed</code>
    <a href="../handler.html">handler</a> also activates the
    INCLUDES filter. As well, Apache will activate the INCLUDES
    filter for any document with mime type
    <code>text/x-server-parsed-html</code> or
    <code>text/x-server-parsed-html3</code> (and the resulting
    output will have the mime type <code>text/html</code>).</p>

    <p>For more information, see our <a href="../howto/ssi.html">Tutorial on Server Side Includes</a>.</p>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="pathinfo" id="pathinfo">PATH_INFO with Server Side Includes</a></h2>
    

    <p>Files processed for server-side includes no longer accept
    requests with <code>PATH_INFO</code> (trailing pathname information)
    by default.  You can use the <code class="directive"><a href="../mod/core.html#acceptpathinfo">AcceptPathInfo</a></code> directive to
    configure the server to accept requests with <code>PATH_INFO</code>.</p>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="elements" id="elements">Basic Elements</a></h2>
    <p>The document is parsed as an HTML document, with special
    commands embedded as SGML comments. A command has the syntax: </p>

    <div class="example"><p><code>
      &lt;!--#<var>element</var> <var>attribute</var>=<var>value</var>
      <var>attribute</var>=<var>value</var> ... --&gt;
    </code></p></div>

    <p>The value will often be enclosed in double quotes, but single
    quotes (<code>'</code>) and backticks (<code>`</code>) are also
    possible. Many commands only allow a single attribute-value pair.
    Note that the comment terminator (<code>--&gt;</code>) should be
    preceded by whitespace to ensure that it isn't considered part of
    an SSI token. Note that the leading <code>&lt;!--#</code> is <em>one</em>
    token and may not contain any whitespaces.</p>

    <p>The allowed elements are listed in the following table:</p>

    <table class="bordered">
    <tr><th>Element</th><th>Description</th></tr>
    <tr><td><code><a href="#element.config">config</a></code></td>
        <td>configure output formats</td></tr>
    <tr><td><code><a href="#element.echo">echo</a></code></td>
        <td>print variables</td></tr>
    <tr><td><code><a href="#element.exec">exec</a></code></td>
        <td>execute external programs</td></tr>
    <tr><td><code><a href="#element.fsize">fsize</a></code></td>
        <td>print size of a file</td></tr>
    <tr><td><code><a href="#element.flastmod">flastmod</a></code></td>
        <td>print last modification time of a file</td></tr>
    <tr><td><code><a href="#element.include">include</a></code></td>
        <td>include a file</td></tr>
    <tr><td><code><a href="#element.printenv">printenv</a></code></td>
        <td>print all available variables</td></tr>
    <tr><td><code><a href="#element.set">set</a></code></td>
        <td>set a value of a variable</td></tr>
    </table>

    <p>SSI elements may be defined by modules other than
    <code class="module"><a href="../mod/mod_include.html">mod_include</a></code>. In fact, the <code><a href="#element.exec">exec</a></code> element is provided by
    <code class="module"><a href="../mod/mod_cgi.html">mod_cgi</a></code>, and will only be available if this
    module is loaded.</p>

    <h3><a name="element.config" id="element.config">The config Element</a></h3>
      <p>This command controls various aspects of the parsing. The
      valid attributes are:</p>

      <dl>
      <dt><code>echomsg</code> (<em>Apache 2.1 and later</em>)</dt>
      <dd>The value is a message that is sent back to the
      client if the <code><a href="#element.echo">echo</a></code> element
      attempts to echo an undefined variable. This overrides any <code class="directive"><a href="#ssiundefinedecho">SSIUndefinedEcho</a></code> directives.</dd>

      <dt><code>errmsg</code></dt>
      <dd>The value is a message that is sent back to the
      client if an error occurs while parsing the
      document. This overrides any <code class="directive"><a href="#ssierrormsg">SSIErrorMsg</a></code> directives.</dd>

      <dt><code>sizefmt</code></dt>
      <dd>The value sets the format to be used which displaying
      the size of a file. Valid values are <code>bytes</code>
      for a count in bytes, or <code>abbrev</code> for a count
      in Kb or Mb as appropriate, for example a size of 1024 bytes
      will be printed as "1K".</dd>

      <dt><code>timefmt</code></dt>
      <dd>The value is a string to be used by the
      <code>strftime(3)</code> library routine when printing
      dates.</dd>
      </dl>
     

    <h3><a name="element.echo" id="element.echo">The echo Element</a></h3>
      <p>This command prints one of the <a href="#includevars">include
      variables</a>, defined below. If the variable is unset, the result is
      determined by the <code class="directive"><a href="#ssiundefinedecho">SSIUndefinedEcho</a></code> directive. Any dates printed are
      subject to the currently configured <code>timefmt</code>.</p>

      <p>Attributes:</p> 

      <dl>
      <dt><code>var</code></dt>
      <dd>The value is the name of the variable to print.</dd>

      <dt><code>encoding</code></dt>
      <dd><p>Specifies how Apache should encode special characters
      contained in the variable before outputting them. If set
      to <code>none</code>, no encoding will be done. If set to
      <code>url</code>, then URL encoding (also known as %-encoding;
      this is appropriate for use within URLs in links, etc.) will be
      performed. At the start of an <code>echo</code> element,
      the default is set to <code>entity</code>, resulting in entity
      encoding (which is appropriate in the context of a block-level
      HTML element, <em>e.g.</em> a paragraph of text). This can be
      changed by adding an <code>encoding</code> attribute, which will
      remain in effect until the next <code>encoding</code> attribute
      is encountered or the element ends, whichever comes first.</p>

      <p>The <code>encoding</code> attribute must <em>precede</em> the
      corresponding <code>var</code> attribute to be effective, and 
      only special characters as defined in the ISO-8859-1 character
      encoding will be encoded. This encoding process may not have the
      desired result if a different character encoding is in use.</p>

      <div class="warning">
        In order to avoid cross-site scripting issues, you should
        <em>always</em> encode user supplied data.
      </div>
      </dd>
      </dl>
     

    <h3><a name="element.exec" id="element.exec">The exec Element</a></h3>
      <p>The <code>exec</code> command executes a given shell command or
      CGI script. It requires <code class="module"><a href="../mod/mod_cgi.html">mod_cgi</a></code> to be present
      in the server. If <code class="directive"><a href="../mod/core.html#options">Options</a></code>
      <code>IncludesNOEXEC</code> is set, this command is completely
      disabled. The valid attributes are:</p>

      <dl>
      <dt><code>cgi</code></dt>
      <dd><p>The value specifies a (%-encoded) URL-path to
      the CGI script. If the path does not begin with a slash (/),
      then it is taken to be relative to the current
      document. The document referenced by this path is
      invoked as a CGI script, even if the server would not
      normally recognize it as such. However, the directory
      containing the script must be enabled for CGI scripts
      (with <code class="directive"><a href="../mod/mod_alias.html#scriptalias">ScriptAlias</a></code>
      or <code class="directive"><a href="../mod/core.html#options">Options</a></code>
      <code>ExecCGI</code>).</p>

      <p>The CGI script is given the <code>PATH_INFO</code> and query
      string (<code>QUERY_STRING</code>) of the original request from the
      client; these <em>cannot</em> be specified in the URL path. The
      include variables will be available to the script in addition to
      the standard <a href="mod_cgi.html">CGI</a> environment.</p>

      <div class="example"><h3>Example</h3><p><code>
        &lt;!--#exec cgi="/cgi-bin/example.cgi" --&gt;
      </code></p></div>

      <p>If the script returns a <code>Location:</code> header instead of
      output, then this will be translated into an HTML anchor.</p>

      <p>The <code><a href="#includevirtual">include virtual</a></code>
      element should be used in preference to <code>exec cgi</code>. In
      particular, if you need to pass additional arguments to a CGI program,
      using the query string, this cannot be done with <code>exec
      cgi</code>, but can be done with <code>include virtual</code>, as
      shown here:</p>

      <div class="example"><p><code>
        &lt;!--#include virtual="/cgi-bin/example.cgi?argument=value" --&gt;
      </code></p></div>
      </dd>

      <dt><code>cmd</code></dt>
      <dd><p>The server will execute the given string using
      <code>/bin/sh</code>. The <a href="#includevars">include variables</a> are available to the command, in addition
      to the usual set of CGI variables.</p>

      <p>The use of <code><a href="#includevirtual">#include virtual</a></code> is almost always prefered to using
      either <code>#exec cgi</code> or <code>#exec cmd</code>. The former
      (<code>#include virtual</code>) uses the standard Apache sub-request
      mechanism to include files or scripts. It is much better tested and
      maintained.</p>

      <p>In addition, on some platforms, like Win32, and on unix when
      using <a href="../suexec.html">suexec</a>, you cannot pass arguments
      to a command in an <code>exec</code> directive, or otherwise include
      spaces in the command. Thus, while the following will work under a
      non-suexec configuration on unix, it will not produce the desired
      result under Win32, or when running suexec:</p>

      <div class="example"><p><code>
        &lt;!--#exec cmd="perl /path/to/perlscript arg1 arg2" --&gt;
      </code></p></div>
      </dd>
      </dl>
     

    <h3><a name="element.fsize" id="element.fsize">The fsize Element</a></h3>
      <p>This command prints the size of the specified file, subject
      to the <code>sizefmt</code> format specification. Attributes:</p>

      <dl>
      <dt><code>file</code></dt>
      <dd>The value is a path relative to the directory
      containing the current document being parsed.</dd>

      <dt><code>virtual</code></dt>
      <dd>The value is a (%-encoded) URL-path. If it does not begin with
      a slash (/) then it is taken to be relative to the current document.
      Note, that this does <em>not</em> print the size of any CGI output,
      but the size of the CGI script itself.</dd>
      </dl>
     

    <h3><a name="element.flastmod" id="element.flastmod">The flastmod Element</a></h3>
      <p>This command prints the last modification date of the
      specified file, subject to the <code>timefmt</code> format
      specification. The attributes are the same as for the
      <code><a href="#element.fsize">fsize</a></code> command.</p>
     

    <h3><a name="element.include" id="element.include">The include Element</a></h3>
      <p>This command inserts the text of another document or file
      into the parsed file. Any included file is subject to the usual
      access control. If the directory containing the parsed file has
      <a href="core.html#options">Options</a>
      <code>IncludesNOEXEC</code> set, then only documents with a text
      <a class="glossarylink" href="../glossary.html#mime-type" title="see glossary">MIME-type</a> (<code>text/plain</code>,
      <code>text/html</code> etc.) will be included. Otherwise CGI
      scripts are invoked as normal using the complete URL given in
      the command, including any query string.</p>

      <p>An attribute defines the location of the document; the
      inclusion is done for each attribute given to the include
      command. The valid attributes are:</p>

      <dl>
      <dt><code>file</code></dt>
      <dd>The value is a path relative to the directory
      containing the current document being parsed. It cannot
      contain <code>../</code>, nor can it be an absolute path.
      Therefore, you cannot include files that are outside of the
      document root, or above the current document in the directory
      structure. The <code>virtual</code> attribute should always be
      used in preference to this one.</dd>

      <dt><code><a id="includevirtual" name="includevirtual">virtual</a></code></dt>
      <dd><p>The value is a (%-encoded) URL-path. The URL cannot contain a
      scheme or hostname, only a path and an optional query string. If it
      does not begin with a slash (/) then it is taken to be relative to the
      current document.</p>

      <p>A URL is constructed from the attribute, and the output the
      server would return if the URL were accessed by the client is
      included in the parsed output. Thus included files can be nested.</p>

      <p>If the specified URL is a CGI program, the program will be
      executed and its output inserted in place of the directive in the
      parsed file. You may include a query string in a CGI url:</p>
     
      <div class="example"><p><code>
        &lt;!--#include virtual="/cgi-bin/example.cgi?argument=value" --&gt;
      </code></p></div>
           
      <p><code>include virtual</code> should be used in preference
      to <code>exec cgi</code> to include the output of CGI programs
      into an HTML document.</p>
      </dd>
      </dl>
     

    <h3><a name="element.printenv" id="element.printenv">The printenv Element</a></h3>
      <p>This prints out a listing of all existing variables and
      their values. Special characters are entity encoded (see the <code><a href="#element.echo">echo</a></code> element for details)
      before being output. There are no attributes.</p>

      <div class="example"><h3>Example</h3><p><code>
        &lt;!--#printenv --&gt;
      </code></p></div>
     

    <h3><a name="element.set" id="element.set">The set Element</a></h3>
      <p>This sets the value of a variable. Attributes:</p>

      <dl>
      <dt><code>var</code></dt>
      <dd>The name of the variable to set.</dd>

      <dt><code>value</code></dt>
      <dd>The value to give a variable.</dd>
      </dl>

      <div class="example"><h3>Example</h3><p><code>
        &lt;!--#set var="category" value="help" --&gt;
      </code></p></div>
     
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="includevars" id="includevars">Include Variables</a></h2>
    

    <p>In addition to the variables in the standard CGI environment,
    these are available for the <code>echo</code> command, for
    <code>if</code> and <code>elif</code>, and to any program
    invoked by the document.</p>

    <dl>
      <dt><code>DATE_GMT</code></dt>
      <dd>The current date in Greenwich Mean Time.</dd>

      <dt><code>DATE_LOCAL</code></dt>
      <dd>The current date in the local time zone.</dd>

      <dt><code>DOCUMENT_NAME</code></dt>
      <dd>The filename (excluding directories) of the document
      requested by the user.</dd>

      <dt><code>DOCUMENT_URI</code></dt>
      <dd>The (%-decoded) URL path of the document requested by the
      user. Note that in the case of nested include files, this is
      <em>not</em> the URL for the current document.</dd>

      <dt><code>LAST_MODIFIED</code></dt>
      <dd>The last modification date of the document requested by
      the user.</dd>

      <dt><code>QUERY_STRING_UNESCAPED</code></dt>
      <dd>If a query string is present, this variable contains the
      (%-decoded) query string, which is <em>escaped</em> for shell
      usage (special characters like <code>&amp;</code> etc. are
      preceded by backslashes).</dd>
    </dl>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="substitution" id="substitution">Variable Substitution</a></h2>

    <p>Variable substitution is done within quoted strings in most
    cases where they may reasonably occur as an argument to an SSI
    directive. This includes the <code>config</code>,
    <code>exec</code>, <code>flastmod</code>, <code>fsize</code>,
    <code>include</code>, <code>echo</code>, and <code>set</code>
    directives, as well as the arguments to conditional operators.
    You can insert a literal dollar sign into the string using backslash
    quoting:</p>

    <div class="example"><p><code>
      &lt;!--#if expr="$a = \$test" --&gt;
    </code></p></div>

    <p>If a variable reference needs to be substituted in the
    middle of a character sequence that might otherwise be
    considered a valid identifier in its own right, it can be
    disambiguated by enclosing the reference in braces,
    <em>a la</em> shell substitution:</p>

    <div class="example"><p><code>
      &lt;!--#set var="Zed" value="${REMOTE_HOST}_${REQUEST_METHOD}" --&gt;
    </code></p></div>

    <p>This will result in the <code>Zed</code> variable being set
    to "<code>X_Y</code>" if <code>REMOTE_HOST</code> is
    "<code>X</code>" and <code>REQUEST_METHOD</code> is
    "<code>Y</code>".</p>

    <p>The below example will print "in foo" if the
    <code>DOCUMENT_URI</code> is <code>/foo/file.html</code>, "in bar"
    if it is <code>/bar/file.html</code> and "in neither" otherwise:</p>

    <div class="example"><p><code>
      &lt;!--#if expr='"$DOCUMENT_URI" = "/foo/file.html"' --&gt;<br />
      <span class="indent">
        in foo<br />
      </span>
      &lt;!--#elif expr='"$DOCUMENT_URI" = "/bar/file.html"' --&gt;<br />
      <span class="indent">
        in bar<br />
      </span>
      &lt;!--#else --&gt;<br />
      <span class="indent">
        in neither<br />
      </span>
      &lt;!--#endif --&gt;
    </code></p></div>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="flowctrl" id="flowctrl">Flow Control Elements</a></h2>
    

    <p>The basic flow control elements are:</p>

    <div class="example"><p><code>
      &lt;!--#if expr="<var>test_condition</var>" --&gt;<br />
      &lt;!--#elif expr="<var>test_condition</var>" --&gt;<br />
      &lt;!--#else --&gt;<br />
      &lt;!--#endif --&gt;
    </code></p></div>

    <p>The <code>if</code> element works like an if statement in a
    programming language. The test condition is evaluated and if
    the result is true, then the text until the next <code>elif</code>,
    <code>else</code> or <code>endif</code> element is included in the
    output stream.</p>

    <p>The <code>elif</code> or <code>else</code> statements are be used
    to put text into the output stream if the original
    <var>test_condition</var> was false. These elements are optional.</p>

    <p>The <code>endif</code> element ends the <code>if</code> element
    and is required.</p>

    <p><var>test_condition</var> is one of the following:</p>

    <dl>
      <dt><code><var>string</var></code></dt>
      <dd>true if <var>string</var> is not empty</dd>

      <dt><code><var>string1</var> = <var>string2</var><br />
      <var>string1</var> == <var>string2</var><br />
      <var>string1</var> != <var>string2</var></code></dt>
      
      <dd><p>Compare <var>string1</var> with <var>string2</var>. If
      <var>string2</var> has the form <code>/<var>string2</var>/</code>
      then it is treated as a regular expression. Regular expressions are
      implemented by the <a href="http://www.pcre.org">PCRE</a> engine and
      have the same syntax as those in <a href="http://www.perl.com">perl
      5</a>. Note that <code>==</code> is just an alias for <code>=</code>
      and behaves exactly the same way.</p>

      <p>If you are matching positive (<code>=</code> or <code>==</code>), you
      can capture grouped parts of the regular expression. The captured parts
      are stored in the special variables <code>$1</code> ..
      <code>$9</code>.</p>

      <div class="example"><h3>Example</h3><p><code>
        &lt;!--#if expr="$QUERY_STRING = /^sid=([a-zA-Z0-9]+)/" --&gt;<br />
        <span class="indent">
          &lt;!--#set var="session" value="$1" --&gt;<br />
        </span>
        &lt;!--#endif --&gt;
      </code></p></div>
      </dd>

      <dt><code><var>string1</var> &lt; <var>string2</var><br />
       <var>string1</var> &lt;= <var>string2</var><br />
       <var>string1</var> &gt; <var>string2</var><br />
       <var>string1</var> &gt;= <var>string2</var></code></dt>

      <dd>Compare <var>string1</var> with <var>string2</var>. Note, that
      strings are compared <em>literally</em> (using
      <code>strcmp(3)</code>). Therefore the string "100" is less than
      "20".</dd>

      <dt><code>( <var>test_condition</var> )</code></dt>
      <dd>true if <var>test_condition</var> is true</dd>

      <dt><code>! <var>test_condition</var></code></dt>
      <dd>true if <var>test_condition</var> is false</dd>

      <dt><code><var>test_condition1</var> &amp;&amp;
        <var>test_condition2</var></code></dt>
      <dd>true if both <var>test_condition1</var> and
      <var>test_condition2</var> are true</dd>

      <dt><code><var>test_condition1</var> ||
        <var>test_condition2</var></code></dt>
      <dd>true if either <var>test_condition1</var> or
      <var>test_condition2</var> is true</dd>
    </dl>

    <p>"<code>=</code>" and "<code>!=</code>" bind more tightly than
    "<code>&amp;&amp;</code>" and "<code>||</code>". "<code>!</code>" binds
    most tightly. Thus, the following are equivalent:</p>

    <div class="example"><p><code>
      &lt;!--#if expr="$a = test1 &amp;&amp; $b = test2" --&gt;<br />
      &lt;!--#if expr="($a = test1) &amp;&amp; ($b = test2)" --&gt;
    </code></p></div>

    <p>The boolean operators <code>&amp;&amp;</code> and <code>||</code>
    share the same priority. So if you want to bind such an operator more
    tightly, you should use parentheses.</p>

    <p>Anything that's not recognized as a variable or an operator
    is treated as a string. Strings can also be quoted:
    <code>'string'</code>. Unquoted strings can't contain whitespace
    (blanks and tabs) because it is used to separate tokens such as
    variables. If multiple strings are found in a row, they are
    concatenated using blanks. So,</p>

    <div class="example"><p><code><var>string1</var>&nbsp;&nbsp;&nbsp;&nbsp;<var>string2</var></code> results in <code><var>string1</var>&nbsp;<var>string2</var></code><br />
      <br />
      and<br />
      <br />
      <code>'<var>string1</var>&nbsp;&nbsp;&nbsp;&nbsp;<var>string2</var>'</code> results in <code><var>string1</var>&nbsp;&nbsp;&nbsp;&nbsp;<var>string2</var></code>.</p></div>

    <div class="note"><h3>Optimization of Boolean Expressions</h3>
      <p>If the expressions become more complex and slow down processing
      significantly, you can try to optimize them according to the
      evaluation rules:</p>
      <ul>
      <li>Expressions are evaluated from left to right</li>
      <li>Binary boolean operators (<code>&amp;&amp;</code> and <code>||</code>)
          are short circuited wherever possible. In conclusion with the rule
          above that means, <code class="module"><a href="../mod/mod_include.html">mod_include</a></code> evaluates at first
          the left expression. If the left result is sufficient to determine
          the end result, processing stops here. Otherwise it evaluates the
          right side and computes the end result from both left and right
          results.</li>
      <li>Short circuit evaluation is turned off as long as there are regular
          expressions to deal with. These must be evaluated to fill in the
          backreference variables (<code>$1</code> .. <code>$9</code>).</li>
      </ul>
      <p>If you want to look how a particular expression is handled, you can
      recompile <code class="module"><a href="../mod/mod_include.html">mod_include</a></code> using the
      <code>-DDEBUG_INCLUDE</code> compiler option. This inserts for every
      parsed expression tokenizer information, the parse tree and how it is
      evaluated into the output sent to the client.</p>
    </div>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="SSIEndTag" id="SSIEndTag">SSIEndTag</a> <a name="ssiendtag" id="ssiendtag">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>String that ends an include element</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>SSIEndTag <var>tag</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>SSIEndTag "--&gt;"</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Base</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_include</td></tr>
<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.0.30 and later.</td></tr>
</table>
    <p>This directive changes the string that <code class="module"><a href="../mod/mod_include.html">mod_include</a></code>
    looks for to mark the end of an include element.</p>

    <div class="example"><h3>Example</h3><p><code>
      SSIEndTag "%&gt;"
    </code></p></div>


<h3>See also</h3>
<ul>
<li><code class="directive"><a href="#ssistarttag">SSIStartTag</a></code></li>
</ul>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="SSIErrorMsg" id="SSIErrorMsg">SSIErrorMsg</a> <a name="ssierrormsg" id="ssierrormsg">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Error message displayed when there is an SSI
error</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>SSIErrorMsg <var>message</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>SSIErrorMsg "[an error occurred while processing this
directive]"</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
<tr><th><a href="directive-dict.html#Override">Override:</a></th><td>All</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Base</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_include</td></tr>
<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.0.30 and later.</td></tr>
</table>
    <p>The <code class="directive">SSIErrorMsg</code> directive changes the error
    message displayed when <code class="module"><a href="../mod/mod_include.html">mod_include</a></code> encounters an
    error. For production servers you may consider changing the default
    error message to <code>"&lt;!-- Error --&gt;"</code> so that
    the message is not presented to the user.</p>

    <p>This directive has the same effect as the <code>&lt;!--#config
    errmsg=<var>message</var> --&gt;</code> element.</p>

    <div class="example"><h3>Example</h3><p><code>
      SSIErrorMsg "&lt;!-- Error --&gt;"
    </code></p></div>

</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="SSIStartTag" id="SSIStartTag">SSIStartTag</a> <a name="ssistarttag" id="ssistarttag">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>String that starts an include element</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>SSIStartTag <var>tag</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>SSIStartTag "&lt;!--#"</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Base</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_include</td></tr>
<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.0.30 and later.</td></tr>
</table>
    <p>This directive changes the string that <code class="module"><a href="../mod/mod_include.html">mod_include</a></code>
    looks for to mark an include element to process.</p>

    <p>You may want to use this option if you have 2 servers parsing the
    output of a file each processing different commands (possibly at
    different times).</p> 

    <div class="example"><h3>Example</h3><p><code>
      SSIStartTag "&lt;%"<br />
      SSIEndTag   "%&gt;"
    </code></p></div>

    <p>The example given above, which also specifies a matching
    <code class="directive"><a href="#ssiendtag">SSIEndTag</a></code>, will 
    allow you to use SSI directives as shown in the example 
    below:</p>

    <div class="example"><h3>SSI directives with alternate start and end tags</h3><p><code>
      &lt;%printenv %&gt;
    </code></p></div>

<h3>See also</h3>
<ul>
<li><code class="directive"><a href="#ssiendtag">SSIEndTag</a></code></li>
</ul>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="SSITimeFormat" id="SSITimeFormat">SSITimeFormat</a> <a name="ssitimeformat" id="ssitimeformat">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Configures the format in which date strings are
displayed</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>SSITimeFormat <var>formatstring</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>SSITimeFormat "%A, %d-%b-%Y %H:%M:%S %Z"</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
<tr><th><a href="directive-dict.html#Override">Override:</a></th><td>All</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Base</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_include</td></tr>
<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.0.30 and later.</td></tr>
</table>
<p>This directive changes the format in which date strings are displayed 
    when echoing <code>DATE</code> environment variables. The
    <var>formatstring</var> is as in <code>strftime(3)</code> from the
    C standard library.</p>

    <p>This directive has the same effect as the <code>&lt;!--#config
    timefmt=<var>formatstring</var> --&gt;</code> element.</p>

    <div class="example"><h3>Example</h3><p><code>
      SSITimeFormat "%R, %B %d, %Y"
    </code></p></div>

    <p>The above directive would cause times to be displayed in the
    format "22:26, June 14, 2002".</p>

</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="SSIUndefinedEcho" id="SSIUndefinedEcho">SSIUndefinedEcho</a> <a name="ssiundefinedecho" id="ssiundefinedecho">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>String displayed when an unset variable is echoed</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>SSIUndefinedEcho <var>string</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>SSIUndefinedEcho "(none)"</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
<tr><th><a href="directive-dict.html#Override">Override:</a></th><td>All</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Base</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_include</td></tr>
<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.0.34 and later.</td></tr>
</table>
    <p>This directive changes the string that <code class="module"><a href="../mod/mod_include.html">mod_include</a></code>
    displays when a variable is not set and "echoed".</p>

    <div class="example"><h3>Example</h3><p><code>
      SSIUndefinedEcho "&lt;!-- undef --&gt;"
    </code></p></div>

</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="XBitHack" id="XBitHack">XBitHack</a> <a name="xbithack" id="xbithack">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Parse SSI directives in files with the execute bit
set</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>XBitHack on|off|full</code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>XBitHack off</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
<tr><th><a href="directive-dict.html#Override">Override:</a></th><td>Options</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Base</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_include</td></tr>
</table>
    <p>The <code class="directive">XBitHack</code> directive controls the parsing
    of ordinary html documents. This directive only affects files associated
    with the <a class="glossarylink" href="../glossary.html#mime-type" title="see glossary">MIME-type</a> <code>text/html</code>. <code class="directive">XBitHack</code> can take on the following values:</p>

    <dl>
      <dt><code>off</code></dt>
      <dd>No special treatment of executable files.</dd>

      <dt><code>on</code></dt>
      <dd>Any <code>text/html</code> file that has the user-execute bit
      set will be treated as a server-parsed html document.</dd>

      <dt><code>full</code></dt>
      <dd>As for <code>on</code> but also test the group-execute bit.
      If it is set, then set the <code>Last-modified</code> date of the
      returned file to be the last modified time of the file. If
      it is not set, then no last-modified date is sent. Setting
      this bit allows clients and proxies to cache the result of
      the request. 

      <div class="note"><h3>Note</h3>
      <p>You would not want to use the full option, unless you assure the
      group-execute bit is unset for every SSI script which might <code>#include</code> a CGI or otherwise produces different output on
      each hit (or could potentially change on subsequent requests).</p>
      </div>
      </dd>
    </dl>

    
</div>
</div>
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