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4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<title>Apache Tutorial: Introduction to Server Side Includes</title>
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4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<h1 align="CENTER">Apache Tutorial: Introduction to Server Side
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncIncludes</h1>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync"#apachetutorial:introductiontoserversideincludes">Apache
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncTutorial: Introduction to Server Side Includes</a></li>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<li><a href="#configuringyourservertopermitssi">Configuring your
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<li><a href="#basicssidirectives">Basic SSI directives</a>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync <li><a href="#modificationdateofthefile">Modification date of the
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync <li><a href="#includingtheresultsofacgiprogram">Including the
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<li><a href="#additionalexamples">Additional examples</a>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<li><a href="#whenwasthisdocumentmodified">When was this document
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<li><a href="#includingastandardfooter">Including a standard
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<li><a href="#whatelsecaniconfig">What else can I config?</a></li>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<li><a href="#executingcommands">Executing commands</a></li>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<li><a href="#advancedssitechniques">Advanced SSI techniques</a>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<li><a href="#settingvariables">Setting variables</a></li>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<li><a href="#conditionalexpressions">Conditional expressions</a></li>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<!-- INDEX END -->
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync"apachetutorial:introductiontoserversideincludes">Apache
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncTutorial: Introduction to Server Side Includes</a></h2>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<td valign="top"><strong>Related Modules</strong><br>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync <a href="/mod/mod_include.html">mod_include</a><br>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<td valign="top"><strong>Related Directives</strong><br>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<a href="/mod/mod_include.html#xbithack">XBitHack</a><br>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<a href="/mod/mod_mime.html#addtype">AddType</a><br>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<a href="/mod/mod_mime.html#addhandler">AddHandler</a><br>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync"/mod/mod_setenvif.html#BrowserMatchNoCase">BrowserMatchNoCase</a><br>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>This HOWTO first appeared in Apache Today
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync(http://www.apachetoday.com/) as a series of three articles. They
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncappear here by arrangement with ApacheToday and Internet.com.</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>This article deals with Server Side Includes, usually called simply
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncSSI. In this article, I'll talk about configuring your server to permit
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncSSI, and introduce some basic SSI techniques for adding dynamic content
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncto your existing HTML pages.</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>In the latter part of the article, we'll talk about some of the
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncsomewhat more advanced things that can be done with SSI, such as
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncconditional statements in your SSI directives.</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>SSI (Server Side Includes) are directives that are placed in HTML
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncpages, and evaluated on the server while the pages are being served.
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncThey let you add dynamically generated content to an existing HTML
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncpage, without having to serve the entire page via a CGI program, or
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncother dynamic technology.</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>The decision of when to use SSI, and when to have your page entirely
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncgenerated by some program, is usually a matter of how much of the page
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncis static, and how much needs to be recalculated every time the page is
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncserved. SSI is a great way to add small pieces of information, such as
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncthe current time. But if a majority of your page is being generated at
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncthe time that it is served, you need to look for some other
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncsolution.</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<h2><a name="configuringyourservertopermitssi">Configuring your
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>To permit SSI on your server, you must have the following directive
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsynceither in your <code>httpd.conf</code> file, or in a
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync Options +Includes
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>This tells Apache that you want to permit files to be parsed for SSI
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncdirectives.</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>Not just any file is parsed for SSI directives. You have to tell
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncApache which files should be parsed. There are two ways to do this. You
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsynccan tell Apache to parse any file with a particular file extension,
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncsuch as <code>.shtml</code>, with the following directives:</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync <FilesMatch "\.shtml[.$]">
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync SetOutputFilter INCLUDES<br>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync </FilesMatch>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>One disadvantage to this approach is that if you wanted to add SSI
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncdirectives to an existing page, you would have to change the name of
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncthat page, and all links to that page, in order to give it a
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<code>.shtml</code> extension, so that those directives would be
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncexecuted.</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>The other method is to use the <code>XBitHack</code> directive:</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync XBitHack on
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p><code>XBitHack</code> tells Apache to parse files for SSI directives
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncif they have the execute bit set. So, to add SSI directives to an
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncexisting page, rather than having to change the file name, you would
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncjust need to make the file executable using <code>chmod</code>.</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>A brief comment about what not to do. You'll occasionally see people
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncrecommending that you just tell Apache to parse all <code>.html</code>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncfiles for SSI, so that you don't have to mess with <code>.shtml</code>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncfile names. These folks have perhaps not heard about
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<code>XBitHack</code>. The thing to keep in mind is that, by doing
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncthis, you're requiring that Apache read through every single file that
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncit sends out to clients, even if they don't contain any SSI directives.
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncThis can slow things down quite a bit, and is not a good idea.</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>Of course, on Windows, there is no such thing as an execute bit to
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncset, so that limits your options a little.</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>In its default configuration, Apache does not send the last modified
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncdate or content length HTTP headers on SSI pages, because these values are
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncdifficult to calculate for dynamic content. This can prevent your
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncdocument from being cached, and result in slower perceived client
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncperformance. There are two ways to solve this:</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<li>Use the <code>XBitHack Full</code> configuration. This tells
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncApache to determine the last modified date by looking only at the date
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncof the originally requested file, ignoring the modification date of
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncany included files. </li>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsynchref="/mod/mod_expires.html">mod_expires</a> to set an explicit
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncexpiration time on your files, thereby letting browsers and proxies
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncknow that it is acceptable to cache them. </li>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<h2><a name="basicssidirectives">Basic SSI directives</a></h2>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync <!--#element attribute=value attribute=value ... -->
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>It is formatted like an HTML comment, so if you don't have SSI
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsynccorrectly enabled, the browser will ignore it, but it will still be
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncvisible in the HTML source. If you have SSI correctly configured, the
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncdirective will be replaced with its results.</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>The element can be one of a number of things, and we'll talk some
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncmore about most of these in the next installment of this series. For
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncnow, here are some examples of what you can do with SSI</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync <!--#echo var="DATE_LOCAL" -->
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>The <code>echo</code> element just spits out the value of a
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncvariable. There are a number of standard variables, which include the
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncwhole set of environment variables that are available to CGI programs.
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncAlso, you can define your own variables with the <code>set</code>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncelement.</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>If you don't like the format in which the date gets printed, you can
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncuse the <code>config</code> element, with a <code>timefmt</code>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncattribute, to modify that formatting.</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync <!--#config timefmt="%A %B %d, %Y" -->
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync Today is <!--#echo var="DATE_LOCAL" -->
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<h3><a name="modificationdateofthefile">Modification date of the
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync This document last modified <!--#flastmod file="index.html" -->
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>This element is also subject to <code>timefmt</code> format
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncconfigurations.</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<h3><a name="includingtheresultsofacgiprogram">Including the
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>This is one of the more common uses of SSI - to output the results
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncof a CGI program, such as everybody's favorite, a ``hit counter.''</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync <!--#include virtual="/cgi-bin/counter.pl" -->
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<h2><a name="additionalexamples">Additional examples</a></h2>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>Following are some specific examples of things you can do in your
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncHTML documents with SSI.</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<h2><a name="whenwasthisdocumentmodified">When was this document
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>Earlier, we mentioned that you could use SSI to inform the user when
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncthe document was most recently modified. However, the actual method for
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncdoing that was left somewhat in question. The following code, placed in
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncyour HTML document, will put such a time stamp on your page. Of course,
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncyou will have to have SSI correctly enabled, as discussed above.</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync <!--#config timefmt="%A %B %d, %Y" -->
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync This file last modified <!--#flastmod file="ssi.shtml" -->
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>Of course, you will need to replace the <code>ssi.shtml</code> with
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncthe actual name of the file that you're referring to. This can be
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncinconvenient if you're just looking for a generic piece of code that
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncyou can paste into any file, so you probably want to use the
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync <!--#config timefmt="%D" -->
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync This file last modified <!--#echo var="LAST_MODIFIED" -->
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>For more details on the <code>timefmt</code> format, go to your
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncfavorite search site and look for <code>ctime</code>. The syntax is the
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<h2><a name="includingastandardfooter">Including a standard
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>If you are managing any site that is more than a few pages, you may
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncfind that making changes to all those pages can be a real pain,
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncparticularly if you are trying to maintain some kind of standard look
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncacross all those pages.</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>Using an include file for a header and/or a footer can reduce the
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncburden of these updates. You just have to make one footer file, and
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncthen include it into each page with the <code>include</code> SSI
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsynccommand. The <code>include</code> element can determine what file to
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncinclude with either the <code>file</code> attribute, or the
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<code>virtual</code> attribute. The <code>file</code> attribute is a
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncfile path, <em>relative to the current directory</em>. That means that
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncit cannot be an absolute file path (starting with /), nor can it
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsynccontain ../ as part of that path. The <code>virtual</code> attribute is
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncprobably more useful, and should specify a URL relative to the document
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncbeing served. It can start with a /, but must be on the same server as
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncthe file being served.</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync <!--#include virtual="/footer.html" -->
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>I'll frequently combine the last two things, putting a
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<code>LAST_MODIFIED</code> directive inside a footer file to be
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncincluded. SSI directives can be contained in the included file, and
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncincludes can be nested - that is, the included file can include another
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncfile, and so on.</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<h2><a name="whatelsecaniconfig">What else can I config?</a></h2>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>In addition to being able to <code>config</code> the time format,
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncyou can also <code>config</code> two other things.</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>Usually, when something goes wrong with your SSI directive, you get
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncthe message</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync [an error occurred while processing this directive]
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>If you want to change that message to something else, you can do so
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncwith the <code>errmsg</code> attribute to the <code>config</code>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncelement:</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync <!--#config errmsg="[It appears that you don't know how to use SSI]" -->
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>Hopefully, end users will never see this message, because you will
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsynchave resolved all the problems with your SSI directives before your
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncsite goes live. (Right?)</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>And you can <code>config</code> the format in which file sizes are
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncreturned with the <code>sizefmt</code> attribute. You can specify
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<code>bytes</code> for a full count in bytes, or <code>abbrev</code>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncfor an abbreviated number in Kb or Mb, as appropriate.</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<h2><a name="executingcommands">Executing commands</a></h2>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>I expect that I'll have an article some time in the coming months
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncabout using SSI with small CGI programs. For now, here's something else
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncthat you can do with the <code>exec</code> element. You can actually
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsynchave SSI execute a command using the shell (<code>/bin/sh</code>, to be
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncprecise - or the DOS shell, if you're on Win32). The following, for
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncexample, will give you a directory listing.</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync <pre>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync <!--#exec cmd="ls" -->
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync </pre>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync <pre>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync <!--#exec cmd="dir" -->
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync </pre>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>You might notice some strange formatting with this directive on
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncWindows, because the output from <code>dir</code> contains the string
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync``<<code>dir</code>>'' in it, which confuses browsers.</p>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<p>Note that this feature is exceedingly dangerous, as it will execute
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncwhatever code happens to be embedded in the <code>exec</code> tag. If
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncyou have any situation where users can edit content on your web pages,
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncsuch as with a ``guestbook'', for example, make sure that you have this
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncfeature disabled. You can allow SSI, but not the <code>exec</code>
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsyncfeature, with the <code>IncludesNOEXEC</code> argument to the
4fd606d1f5abe38e1f42c38de1d2e895166bd0f4vboxsync<h2><a name="advancedssitechniques">Advanced SSI techniques</a></h2>