ssi.html.en

Apache V2.0.15 Alpha For Linuxhttpd-2_0_15-alpha.tar.Z

</pre>

<hr>
<h2><a name="additionalexamples">Additional examples</a></h2>

<p>Following are some specific examples of things you can do in your
HTML documents with SSI.</p>

<hr>
<h2><a name="whenwasthisdocumentmodified">When was this document
modified?</a></h2>

<p>Earlier, we mentioned that you could use SSI to inform the user when
the document was most recently modified. However, the actual method for
doing that was left somewhat in question. The following code, placed in
your HTML document, will put such a time stamp on your page. Of course,
you will have to have SSI correctly enabled, as discussed above.</p>

<pre>
        &lt;!--#config timefmt="%A %B %d, %Y" --&gt;
        This file last modified &lt;!--#flastmod file="ssi.shtml" --&gt;
</pre>

<p>Of course, you will need to replace the <code>ssi.shtml</code> with
the actual name of the file that you're referring to. This can be
inconvenient if you're just looking for a generic piece of code that
you can paste into any file, so you probably want to use the
<code>LAST_MODIFIED</code> variable instead:</p>

<pre>
        &lt;!--#config timefmt="%D" --&gt;
        This file last modified &lt;!--#echo var="LAST_MODIFIED" --&gt;
</pre>

<p>For more details on the <code>timefmt</code> format, go to your
favorite search site and look for <code>ctime</code>. The syntax is the
same.</p>

<hr>
<h2><a name="includingastandardfooter">Including a standard
footer</a></h2>

<p>If you are managing any site that is more than a few pages, you may
find that making changes to all those pages can be a real pain,
particularly if you are trying to maintain some kind of standard look
across all those pages.</p>

<p>Using an include file for a header and/or a footer can reduce the
burden of these updates. You just have to make one footer file, and
then include it into each page with the <code>include</code> SSI
command. The <code>include</code> element can determine what file to
include with either the <code>file</code> attribute, or the
<code>virtual</code> attribute. The <code>file</code> attribute is a
file path, <em>relative to the current directory</em>. That means that
it cannot be an absolute file path (starting with /), nor can it
contain ../ as part of that path. The <code>virtual</code> attribute is
probably more useful, and should specify a URL relative to the document
being served. It can start with a /, but must be on the same server as
the file being served.</p>

<pre>
        &lt;!--#include virtual="/footer.html" --&gt;
</pre>

<p>I'll frequently combine the last two things, putting a
<code>LAST_MODIFIED</code> directive inside a footer file to be
included. SSI directives can be contained in the included file, and
includes can be nested - that is, the included file can include another
file, and so on.</p>

<hr>
<h2><a name="whatelsecaniconfig">What else can I config?</a></h2>

<p>In addition to being able to <code>config</code> the time format,
you can also <code>config</code> two other things.</p>

<p>Usually, when something goes wrong with your SSI directive, you get
the message</p>

<pre>
        [an error occurred while processing this directive]
</pre>

<p>If you want to change that message to something else, you can do so
with the <code>errmsg</code> attribute to the <code>config</code>
element:</p>

<pre>
        &lt;!--#config errmsg="[It appears that you don't know how to use SSI]" --&gt;
</pre>

<p>Hopefully, end users will never see this message, because you will
have resolved all the problems with your SSI directives before your
site goes live. (Right?)</p>

<p>And you can <code>config</code> the format in which file sizes are
returned with the <code>sizefmt</code> attribute. You can specify
<code>bytes</code> for a full count in bytes, or <code>abbrev</code>
for an abbreviated number in Kb or Mb, as appropriate.</p>

<hr>
<h2><a name="executingcommands">Executing commands</a></h2>

<p>I expect that I'll have an article some time in the coming months
about using SSI with small CGI programs. For now, here's something else
that you can do with the <code>exec</code> element. You can actually
have SSI execute a command using the shell (<code>/bin/sh</code>, to be
precise - or the DOS shell, if you're on Win32). The following, for
example, will give you a directory listing.</p>

<pre>
        &lt;pre&gt;
        &lt;!--#exec cmd="ls" --&gt;
        &lt;/pre&gt;
</pre>

<p>or, on Windows</p>

<pre>
        &lt;pre&gt;
        &lt;!--#exec cmd="dir" --&gt;
        &lt;/pre&gt;
</pre>

<p>You might notice some strange formatting with this directive on
Windows, because the output from <code>dir</code> contains the string
``&lt;<code>dir</code>&gt;'' in it, which confuses browsers.</p>

<p>Note that this feature is exceedingly dangerous, as it will execute
whatever code happens to be embedded in the <code>exec</code> tag. If
you have any situation where users can edit content on your web pages,
such as with a ``guestbook'', for example, make sure that you have this
feature disabled. You can allow SSI, but not the <code>exec</code>
feature, with the <code>IncludesNOEXEC</code> argument to the
<code>Options</code> directive.</p>

<hr>
<h2><a name="advancedssitechniques">Advanced SSI techniques</a></h2>

<p>In addition to spitting out content, Apache SSI gives you the option
of setting variables, and using those variables in comparisons and
conditionals.</p>

<h3><a name="caveat">Caveat</a></h3>

<p>Most of the features discussed in this article are only available to
you if you are running Apache 1.2 or later. Of course, if you are not
running Apache 1.2 or later, you need to upgrade immediately, if not
sooner. Go on. Do it now. We'll wait.</p>

<hr>
<h2><a name="settingvariables">Setting variables</a></h2>

<p>Using the <code>set</code> directive, you can set variables for
later use. We'll need this later in the discussion, so we'll talk about
it here. The syntax of this is as follows:</p>

<pre>
        &lt;!--#set var="name" value="Rich" --&gt;
</pre>

<p>In addition to merely setting values literally like that, you can
use any other variable, including, for example, environment variables,
or some of the variables we discussed in the last article (like
<code>LAST_MODIFIED</code>, for example) to give values to your
variables. You will specify that something is a variable, rather than a
literal string, by using the dollar sign ($) before the name of the
variable.</p>

<pre>
        &lt;!--#set var="modified" value="$LAST_MODIFIED" --&gt;
</pre>

<p>To put a literal dollar sign into the value of your variable, you
need to escape the dollar sign with a backslash.</p>

<pre>
        &lt;!--#set var="cost" value="\$100" --&gt;
</pre>

<p>Finally, if you want to put a variable in the midst of a longer
string, and there's a chance that the name of the variable will run up
against some other characters, and thus be confused with those
characters, you can place the name of the variable in braces, to remove
this confusion. (It's hard to come up with a really good example of
this, but hopefully you'll get the point.)</p>

<pre>
        &lt;!--#set var="date" value="${DATE_LOCAL}_${DATE_GMT}" --&gt;
</pre>

<hr>
<h2><a name="conditionalexpressions">Conditional expressions</a></h2>

<p>Now that we have variables, and are able to set and compare their
values, we can use them to express conditionals. This lets SSI be a
tiny programming language of sorts. <code>mod_include</code> provides
an <code>if</code>, <code>elif</code>, <code>else</code>,
<code>endif</code> structure for building conditional statements. This
allows you to effectively generate multiple logical pages out of one
actual page.</p>

<p>The structure of this conditional construct is:</p>

<pre>
        &lt;!--#if expr="test_condition" --&gt;
    &lt;!--#elif expr="test_condition" --&gt;
    &lt;!--#else --&gt;
    &lt;!--#endif --&gt;
</pre>

<p>A <em>test_condition</em> can be any sort of logical comparison -
either comparing values to one another, or testing the ``truth'' of a
particular value. (A given string is true if it is nonempty.) For a
full list of the comparison operators available to you, see the
<code>mod_include</code> documentation. Here are some examples of how
one might use this construct.</p>

<p>In your configuration file, you could put the following line:</p>

<pre>
        BrowserMatchNoCase macintosh Mac
        BrowserMatchNoCase MSIE InternetExplorer
</pre>

<p>This will set environment variables ``Mac'' and ``InternetExplorer''
to true, if the client is running Internet Explorer on a Macintosh.</p>

<p>Then, in your SSI-enabled document, you might do the following:</p>

<pre>
        &lt;!--#if expr="${Mac} &amp;&amp; ${InternetExplorer}" --&gt;
        Apologetic text goes here
        &lt;!--#else --&gt;
        Cool JavaScript code goes here
        &lt;!--#endif --&gt;
</pre>

<p>Not that I have anything against IE on Macs - I just struggled for a
few hours last week trying to get some JavaScript working on IE on a
Mac, when it was working everywhere else. The above was the interim
workaround.</p>

<p>Any other variable (either ones that you define, or normal
environment variables) can be used in conditional statements. With
Apache's ability to set environment variables with the
<code>SetEnvIf</code> directives, and other related directives, this
functionality can let you do some pretty involved dynamic stuff without
ever resorting to CGI.</p>

<hr>
<h2><a name="conclusion">Conclusion</a></h2>

<p>SSI is certainly not a replacement for CGI, or other technologies
used for generating dynamic web pages. But it is a great way to add
small amounts of dynamic content to pages, without doing a lot of extra
work.</p>
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