<?xml version="1.0"?>

<!DOCTYPE modulesynopsis SYSTEM "/style/modulesynopsis.dtd">

<?xml-stylesheet type="text/xsl" href="/style/manual.en.xsl"?>

<modulesynopsis metafile="mod_include.xml.meta">

<name>mod_include</name>

<description>Server-parsed html documents (Server Side Includes)</description>

<status>Base</status>

<sourcefile>mod_include.c</sourcefile>

<identifier>include_module</identifier>

<compatibility>Implemented as an output filter since Apache

2.0</compatibility>

<summary>

<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>

</summary>

<seealso><directive module="core">Options</directive></seealso>

<seealso><directive module="core">AcceptPathInfo</directive></seealso>

<seealso><a href="/filter.html">Filters</a></seealso>

<seealso><a href="/howto/ssi.html">SSI Tutorial</a></seealso>

<section id="enabling">

<title>Enabling Server-Side Includes</title>

<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>

<highlight language="config">

AddType text/html .shtml

AddOutputFilter INCLUDES .shtml

</highlight>

<p>The following directive must be given for the directories

containing the shtml files (typically in a

<directive module="core" type="section">Directory</directive> section,

but this directive is also valid in <code>.htaccess</code> files if

<directive module="core">AllowOverride</directive> <code>Options</code>

is set):</p>

<highlight language="config">

Options +Includes

</highlight>

<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>

</section> <!-- /enabling -->

<section id="pathinfo">

<title>PATH_INFO with Server Side Includes</title>

<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 <directive

module="core">AcceptPathInfo</directive> directive to

configure the server to accept requests with <code>PATH_INFO</code>.</p>

</section> <!-- /pathinfo -->

<section id="elements"><title>Basic Elements</title>

<p>The document is parsed as an HTML document, with special

commands embedded as SGML comments. A command has the syntax: </p>

<example>

&lt;!--#<var>element</var> <var>attribute</var>=<var>value</var>

<var>attribute</var>=<var>value</var> ... --&gt;

</example>

<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 border="1">

<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

<module>mod_include</module>. In fact, the <code><a

href="#element.exec">exec</a></code> element is provided by

<module>mod_cgi</module>, and will only be available if this

module is loaded.</p>

<section id="element.config"><title>The config Element</title>

<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 <directive

module="mod_include">SSIUndefinedEcho</directive> 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 <directive

module="mod_include">SSIErrorMsg</directive> directives.</dd>

<dt><code>sizefmt</code></dt>

<dd>The value sets the format to be used when 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>

</section> <!-- /config -->

<section id="element.echo"><title>The echo Element</title>

<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 <directive module="mod_include"

>SSIUndefinedEcho</directive> 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>decoding</code></dt>

<dd><p>Specifies whether Apache should strip an encoding from

the variable before processing the variable further. The default

is <code>none</code>, where no decoding will be done. If set to

<code>url</code>, then URL decoding (also known as %-encoding;

this is appropriate for use within URLs in links, etc.) will be

performed. If set to <code>urlencoded</code>,

application/x-www-form-urlencoded compatible encoding (found in

query strings) will be stripped. If set to <code>base64</code>,

base64 will be decoded, and if set to <code>entity</code>, HTML

entity encoding will be stripped. Decoding is done prior to any

further encoding on the variable. Multiple encodings can be

stripped by specifying more than one comma separated encoding.

The decoding setting will remain in effect until the next decoding

attribute is encountered, or the element ends.</p>

<p>The <code>decoding</code> attribute must <em>precede</em> the

corresponding <code>var</code> attribute to be effective.</p>

</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. If set to <code>urlencoded</code>,

application/x-www-form-urlencoded compatible encoding will be

performed instead, and should be used with query strings. If set

to <code>base64</code>, base64 encoding 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.</p>

<note type="warning">

In order to avoid cross-site scripting issues, you should

<em>always</em> encode user supplied data.

</note>

</dd>

</dl>

</section> <!-- /echo -->

<section id="element.exec"><title>The exec Element</title>

<p>The <code>exec</code> command executes a given shell command or

CGI script. It requires <module>mod_cgi</module> to be present

in the server. If <directive module="core">Options</directive>

<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 <directive module="mod_alias">ScriptAlias</directive>

or <directive module="core">Options</directive>

<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>

<example><title>Example</title>

&lt;!--#exec cgi="/cgi-bin/example.cgi" --&gt;

</example>

<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>

<example>

&lt;!--#include virtual="/cgi-bin/example.cgi?argument=value" --&gt;

</example>

</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>

<example>

&lt;!--#exec cmd="perl /path/to/perlscript arg1 arg2" --&gt;

</example>

</dd>

</dl>

</section> <!-- /exec -->

<section id="element.fsize"><title>The fsize Element</title>

<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>

</section> <!-- /fsize -->

<section id="element.flastmod"><title>The flastmod Element</title>

<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>

</section> <!-- /flastmod -->

<section id="element.include"><title>The include Element</title>

<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

<glossary>MIME-type</glossary> (<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, and may

appear more than once in an include element; an inclusion is

done for each attribute given to the include command in turn.

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>

<example>

&lt;!--#include virtual="/cgi-bin/example.cgi?argument=value" --&gt;

</example>

<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>

<p>If the <directive module="mod_request">KeptBodySize</directive>

directive is correctly configured and valid for this included

file, attempts to POST requests to the enclosing HTML document

will be passed through to subrequests as POST requests as well.

Without the directive, all subrequests are processed as GET

requests.</p>

</dd>

<dt><code>onerror</code></dt>

<dd><p>The value is a (%-encoded) URL-path which is shown should a

previous attempt to include a file or virtual attribute failed.

To be effective, this attribute must be specified after the

file or virtual attributes being covered. If the attempt to

include the onerror path fails, or if onerror is not specified, the

default error message will be included.</p>

<example>

# Simple example<br />

&lt;!--#include virtual="/not-exist.html" onerror="/error.html" --&gt;

</example>

<example>

# Dedicated onerror paths<br />

&lt;!--#include virtual="/path-a.html" onerror="/error-a.html" virtual="/path-b.html" onerror="/error-b.html" --&gt;

</example>

</dd>

</dl>

</section> <!-- /include -->

<section id="element.printenv"><title>The printenv Element</title>

<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>

<example><title>Example</title>

&lt;!--#printenv --&gt;

</example>

</section> <!-- /printenv -->

<section id="element.set"><title>The set Element</title>

<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>

<dt><code>decoding</code></dt>

<dd><p>Specifies whether Apache should strip an encoding from

the variable before processing the variable further. The default

is <code>none</code>, where no decoding will be done. If set to

<code>url</code>, <code>urlencoded</code>, <code>base64</code>

or <code>entity</code>, URL decoding,

application/x-www-form-urlencoded decoding, base64 decoding or HTML

entity decoding will be performed respectively. More than one

decoding can be specified by separating with commas. The decoding

setting will remain in effect until the next decoding attribute

is encountered, or the element ends. The <code>decoding</code>

attribute must <em>precede</em> the corresponding

<code>var</code> attribute to be effective.</p>

</dd>

<dt><code>encoding</code></dt>

<dd><p>Specifies how Apache should encode special characters

contained in the variable before setting them. The default is

<code>none</code>, where no encoding will be done. If set to

<code>url</code>, <code>urlencoding</code>, <code>base64</code>

or <code>entity</code>, URL encoding,

application/x-www-form-urlencoded encoding, base64 encoding or

HTML entity encoding will be performed respectively. More than

one encoding can be specified by separating with commas. The

encoding setting will remain in effect until the next encoding

attribute is encountered, or the element ends. The

<code>encoding</code> attribute must <em>precede</em> the

corresponding <code>var</code> attribute to be effective.

Encodings are applied after all decodings have been

stripped.</p>

</dd>

</dl>

<example><title>Example</title>

&lt;!--#set var="category" value="help" --&gt;

</example>

</section> <!-- /set -->

</section> <!-- /basic elements -->

<section id="includevars">

<title>Include Variables</title>

<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. Note also that

if the URL is modified internally (e.g. by an <directive

module="mod_alias">alias</directive> or <directive

module="mod_dir">directoryindex</directive>), the modified

URL is shown.</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>

</section>

<section id="substitution"><title>Variable Substitution</title>

<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. If <directive module="mod_include"

>SSILegacyExprParser</directive> is set to <code>on</code>,

substitution also occures in the arguments to conditional operators.

You can insert a literal dollar sign into the string using backslash

quoting:</p>

<example>

&lt;!--#set var="cur" value="\$test" --&gt;

</example>

<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>

<example>

&lt;!--#set var="Zed" value="${REMOTE_HOST}_${REQUEST_METHOD}" --&gt;

</example>

<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>

</section>

<section id="flowctrl">

<title>Flow Control Elements</title>

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

<example>

&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;

</example>

<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 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 a boolean expression tha follows the

<a href="/expr.html">ap_expr</a> syntax. The syntax can be changed

to be compatible with Apache HTTPD 2.2.x using <directive

module="mod_include">SSILegacyExprParser</directive>.</p>

<p>The SSI variables set with the <code>var</code> element are exported

into the request environment and can be accessed with the

<code>reqenv</code> function. As a short-cut, the function name

<code>v</code> is also available inside <module>mod_include</module>.</p>

<p>The below example will print "from local net" if client IP address

belongs to the 10.0.0.0/8 subnet.</p>

<example>

&lt;!--#if expr='-R "10.0.0.0/8"' --&gt;<br />

<indent>

from local net<br />

</indent>

&lt;!--#else --&gt;<br />

<indent>

from somewhere else<br />

</indent>

&lt;!--#endif --&gt;

</example>

<p>The below example will print "foo is bar" if the variable

<code>foo</code> is set to the value "bar".</p>

<example>

&lt;!--#if expr='v("foo") = "bar"' --&gt;<br />

<indent>

foo is bar<br />

</indent>

&lt;!--#endif --&gt;

</example>

<note><title>Reference Documentation</title>

<p>See also: <a href="/expr.html">Expressions in Apache HTTP Server</a>,

for a complete reference and examples. The <em>restricted</em> functions

are not available inside <module>mod_include</module></p>

</note>

</section>

<section id="legacyexpr">

<title>Legacy expression syntax</title>

<p>This section describes the syntax of the <code>#if expr</code>

element if <directive module="mod_include">SSILegacyExprParser</directive>

is set to <code>on</code>.</p>

<dl>

<dt><code><var>string</var></code></dt>

<dd>true if <var>string</var> is not empty</dd>

<dt><code><var>-A string</var></code></dt>

<dd><p>true if the URL represented by the string is accessible by

configuration, false otherwise. This is useful where content on a

page is to be hidden from users who are not authorized to view the

URL, such as a link to that URL. Note that the URL is only tested

for whether access would be granted, not whether the URL exists.</p>

<example><title>Example</title>

&lt;!--#if expr="-A /private" --&gt;<br />

<indent>

Click &lt;a href="/private"&gt;here&lt;/a&gt; to access private

information.<br />

</indent>

&lt;!--#endif --&gt;

</example>

</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>. The whole string matched by the regular expression is

stored in the special variable <code>$0</code></p>

<example><title>Example</title>

&lt;!--#if expr="$QUERY_STRING = /^sid=([a-zA-Z0-9]+)/" --&gt;<br />

<indent>

&lt;!--#set var="session" value="$1" --&gt;<br />

</indent>

&lt;!--#endif --&gt;

</example>

</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>

<example>

&lt;!--#if expr="$a = test1 &amp;&amp; $b = test2" --&gt;<br />

&lt;!--#if expr="($a = test1) &amp;&amp; ($b = test2)" --&gt;

</example>

<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>

<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>

</example>

<note><title>Optimization of Boolean Expressions</title>

<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, <module>mod_include</module> 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 <module>mod_include</module> 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>

</note>

<note><title>Escaping slashes in regex strings</title>

<p>All slashes which are not intended to act as delimiters in your regex must

be escaped. This is regardless of their meaning to the regex engine.</p>

</note>

</section>

<directivesynopsis>

<name>SSIEndTag</name>

<description>String that ends an include element</description>

<syntax>SSIEndTag <var>tag</var></syntax>

<default>SSIEndTag &quot;--&gt;&quot;</default>

<contextlist><context>server config</context><context>virtual host</context>

</contextlist>

<compatibility>Available in version 2.0.30 and later.</compatibility>

<usage>

<p>This directive changes the string that <module>mod_include</module>

looks for to mark the end of an include element.</p>

<highlight language="config">

SSIEndTag "%&gt;"

</highlight>

</usage>

<seealso><directive module="mod_include">SSIStartTag</directive></seealso>

</directivesynopsis>

<directivesynopsis>

<name>SSIUndefinedEcho</name>

<description>String displayed when an unset variable is echoed</description>

<syntax>SSIUndefinedEcho <var>string</var></syntax>

<default>SSIUndefinedEcho &quot;(none)&quot;</default>

<contextlist><context>server config</context><context>virtual host</context>

<context>directory</context><context>.htaccess</context></contextlist>

<override>All</override>

<compatibility>Available in version 2.0.34 and later.</compatibility>

<usage>

<p>This directive changes the string that <module>mod_include</module>

displays when a variable is not set and &quot;echoed&quot;.</p>

<highlight language="config">

SSIUndefinedEcho "&lt;!-- undef --&gt;"

</highlight>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>SSIErrorMsg</name>

<description>Error message displayed when there is an SSI

error</description>

<syntax>SSIErrorMsg <var>message</var></syntax>

<default>SSIErrorMsg &quot;[an error occurred while processing this

directive]&quot;</default>

<contextlist><context>server config</context><context>virtual host</context>

<context>directory</context><context>.htaccess</context></contextlist>

<override>All</override>

<compatibility>Available in version 2.0.30 and later.</compatibility>

<usage>

<p>The <directive>SSIErrorMsg</directive> directive changes the error

message displayed when <module>mod_include</module> encounters an

error. For production servers you may consider changing the default

error message to <code>&quot;&lt;!-- Error --&gt;&quot;</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>

<highlight language="config">

SSIErrorMsg "&lt;!-- Error --&gt;"

</highlight>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>SSIStartTag</name>

<description>String that starts an include element</description>

<syntax>SSIStartTag <var>tag</var></syntax>

<default>SSIStartTag &quot;&lt;!--#&quot;</default>

<contextlist><context>server config</context><context>virtual host</context>

</contextlist>

<compatibility>Available in version 2.0.30 and later.</compatibility>

<usage>

<p>This directive changes the string that <module>mod_include</module>

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>

<highlight language="config">

SSIStartTag "&lt;%"<br />

SSIEndTag "%&gt;"

</highlight>

<p>The example given above, which also specifies a matching

<directive module="mod_include">SSIEndTag</directive>, will

allow you to use SSI directives as shown in the example

below:</p>

<example><title>SSI directives with alternate start and end tags</title>

&lt;%printenv %&gt;

</example>

</usage>

<seealso><directive module="mod_include">SSIEndTag</directive></seealso>

</directivesynopsis>

<directivesynopsis>

<name>SSITimeFormat</name>

<description>Configures the format in which date strings are

displayed</description>

<syntax>SSITimeFormat <var>formatstring</var></syntax>

<default>SSITimeFormat &quot;%A, %d-%b-%Y %H:%M:%S %Z&quot;</default>

<contextlist>

<context>server config</context><context>virtual host</context>

<context>directory</context><context>.htaccess</context></contextlist>

<override>All</override>

<compatibility>Available in version 2.0.30 and later.</compatibility>

<usage>

<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>

<highlight language="config">

SSITimeFormat "%R, %B %d, %Y"

</highlight>

<p>The above directive would cause times to be displayed in the

format "22:26, June 14, 2002".</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>SSIETag</name>

<description>Controls whether ETags are generated by the server.</description>

<syntax>SSIETag on|off</syntax>

<default>SSIETag off</default>

<contextlist><context>directory</context><context>.htaccess</context></contextlist>

<compatibility>Available in version 2.2.15 and later.</compatibility>

<usage>

<p>Under normal circumstances, a file filtered by <module>mod_include</module>

may contain elements that are either dynamically generated, or that may

have changed independently of the original file. As a result, by default

the server is asked not to generate an <code>ETag</code> header for the

response by adding <code>no-etag</code> to the request notes.</p>

<p>The <directive>SSIETag</directive> directive suppresses this

behaviour, and allows the server to generate an <code>ETag</code> header.

This can be used to enable caching of the output. Note that a backend server

or dynamic content generator may generate an ETag of its own, ignoring

<code>no-etag</code>, and this ETag will be passed by

<module>mod_include</module> regardless of the value of this setting.

<directive>SSIETag</directive> can take on the following values:</p>

<dl>

<dt><code>off</code></dt>

<dd><code>no-etag</code> will be added to the request notes, and the server

is asked not to generate an ETag. Where a server ignores the value of

<code>no-etag</code> and generates an ETag anyway, the ETag will be

respected.</dd>

<dt><code>on</code></dt>

<dd>Existing ETags will be respected, and ETags generated by the server will

be passed on in the response.</dd>

</dl>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>SSILastModified</name>

<description>Controls whether <code>Last-Modified</code> headers are generated by the

server.</description>

<syntax>SSILastModified on|off</syntax>

<default>SSILastModified off</default>

<contextlist><context>directory</context><context>.htaccess</context></contextlist>

<compatibility>Available in version 2.2.15 and later.</compatibility>

<usage>

<p>Under normal circumstances, a file filtered by <module>mod_include</module>

may contain elements that are either dynamically generated, or that may

have changed independently of the original file. As a result, by default

the <code>Last-Modified</code> header is stripped from the response.</p>

<p>The <directive>SSILastModified</directive> directive overrides this

behaviour, and allows the <code>Last-Modified</code> header to be respected

if already present, or set if the header is not already present. This can

be used to enable caching of the output. <directive>SSILastModified</directive>

can take on the following values:</p>

<dl>

<dt><code>off</code></dt>

<dd>The <code>Last-Modified</code> header will be stripped from responses,

unless the <directive module="mod_include">XBitHack</directive> directive

is set to <code>full</code> as described below.</dd>

<dt><code>on</code></dt>

<dd>The <code>Last-Modified</code> header will be respected if already

present in a response, and added to the response if the response is a

file and the header is missing. The

<directive module="mod_include">SSILastModified</directive> directive

takes precedence over <directive module="mod_include">XBitHack</directive>.</dd>

</dl>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>SSILegacyExprParser</name>

<description>Enable compatibility mode for conditional expressions.</description>

<syntax>SSILegacyExprParser on|off</syntax>

<default>SSILegacyExprParser off</default>

<contextlist><context>directory</context><context>.htaccess</context></contextlist>

<compatibility>Available in version 2.3.13 and later.</compatibility>

<usage>

<p>As of version 2.3.13, <module>mod_include</module> has switched to the

new <a href="/expr.html">ap_expr</a> syntax for conditional expressions

in <code>#if</code> flow control elements. This directive allows to

switch to the <a href="#legacyexpr">old syntax</a> which is compatible

with Apache HTTPD version 2.2.x and earlier.

</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>XBitHack</name>

<description>Parse SSI directives in files with the execute bit

set</description>

<syntax>XBitHack on|off|full</syntax>

<default>XBitHack off</default>

<contextlist><context>server config</context><context>virtual host</context>

<context>directory</context><context>.htaccess</context></contextlist>

<override>Options</override>

<usage>

<p>The <directive>XBitHack</directive> directive controls the parsing

of ordinary html documents. This directive only affects files associated

with the <glossary>MIME-type</glossary> <code>text/html</code>. <directive

>XBitHack</directive> 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.

<note><title>Note</title>

<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>

<p>The <directive module="mod_include">SSILastModified</directive>

directive takes precedence over the

<directive module="mod_include">XBitHack</directive> directive when

<directive module="mod_include">SSILastModified</directive> is set to

<code>on</code>.</p>

</note>

</dd>

</dl>

</usage>

</directivesynopsis>

</modulesynopsis>