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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd">
<html><head>
<title>SquidGuard </title>
<meta name="keywords" content="Squidguard, Squid, Redirector, Proxy, Download, URL, Blacklist, Patches, Source, Software">
<meta name="distribution" content="global">
<link rel="Shortcut Icon" href="/favicon.ico" type="image/x-icon" />
</head>
<body bgcolor="#F0FFFF">
<table bgcolor="#001199" width=100%>
<tr><td bgcolor="#8EE5EE">
<center>
<h2><img alt="" src="/Logos/squidGuard.gif" align=middle> SquidGuard </h2>
</center>
<table border=0 bgcolor="#001199" width=100%>
<tr>
<th><a href="/index.html" target=_top><font color=white>HOME</font></a></th>
<th><a href="/download.html" target=_top><font color=white>Downloads</font></a></th>
<th><a href="/Doc/" target=_top><font color=white>Documentation</font></a></th>
<th><a href="/Devel/" target=_top><font color=white>Development</font></a></th>
<th><a href="/blacklists.html" target=_top><font color=white>Blacklists</font></a></th>
<th><a href="/Contrib/" target=_top><font color=white>Contributions</font></a></th>
<th><a href="/impressum.html" target=body><font color=white>Contact</font></a></th>
</tr>
</table>
<table border=0 width=100%>
<tr><td width=85% bgcolor="#8EE5EE" valign=top>
<br><br>
<h2> Using Expressionlists in SquidGuard</h2>
<br>
<center>
<table width=97%>
<tr><td align=left>
You will never be able to add a possible "bad" pages to your
domains and urls files. To achieve additional blocking
expressionlists can be used.<br>
In an expressionlist you enter words that are mostly likely
part of unwanted domains and urls. Each domains and url
will be matched against the entries found in the configured
expression lists.<br>
<b>Attention:</b> Only use expressionlists if you are sure
you do not block away innocent sites. Additionally keep in
mind that using these lists can result in a noticable
performance impact.
<br><br>
<ol>
<li> <b>Adding expression lists to the configuration</b><br><br>
Expression lists are included in the <em>dest</em> tag.
The example below shows the relevant part of the squidGuard
configuration file:
<br><br>
<table width="75%" cellpadding="0" cellspacing="0" style="background-color: #f2fff0; border: solid 1px #4455bb;">
<tr>
<td style="background-color: #223499; border-bottom: 1px solid #888;">
<font size="-1" color=white>Using expression lists to block porn </font>
</td></tr>
<tr>
<td>
<pre> dest porn {
domainlist porn/domains
urllist porn/urls
expressionlist porn/expressions
}
</pre>
</td></tr>
</table>
<br><br>
You can add an expression list to each defined destination if
you find this necessary (reminder: performance!). SquidGuard
expects the expression file relative to the defined dbhome just
as the domains and urls files.<br>
<br>
<li> <b>Syntax of expression lists</b><br><br>
The expressionlist file format is lines with regular expressions as described
in regex(5). Of most interrest is:<br><br>
<TABLE CELLPADDING=4 BORDER=0>
<TR>
<TH width=20% VALIGN=TOP>
<A NAME="Regular expressions"></A> <TT><B>.</B></TT>
</TH>
<TD VALIGN=TOP>
Matches any single character (use "<TT>\.</TT>" to match a
"<TT>.</TT>").
</TD>
</TR>
<TR>
<TH VALIGN=TOP>
<TT><B>[abc]</B></TT>
</TH>
<TD VALIGN=TOP>
Matches one of the characters ("<TT>[abc]</TT>" matches a
single "<TT>a</TT>" <U>or</U> "<TT>b</TT>" <U>or</U>
"<TT>c</TT>").
</TD>
</TR>
<TR>
<TH VALIGN=TOP>
<TT><B>[c-g]</B></TT>
</TH>
<TD VALIGN=TOP>
Matches one of the characters in the range ("<TT>[c-g]</TT>"
matches a single "<TT>c</TT>" <U>or</U> "<TT>d</TT>" <U>or</U>
"<TT>e</TT>" <U>or</U> "<TT>f</TT>" <U>or</U> "<TT>g</TT>".<BR>
"<TT>[a-z0-9]</TT>" matches any single letter or digit.<BR>
"<TT>[-/.:?]</TT>" matches any single "<TT>-</TT>" <U>or</U>
"<TT>/</TT>" <U>or</U> "<TT>.</TT>" <U>or</U> "<TT>:</TT>"
<U>or</U> "<TT>?</TT>".).
</TD>
</TR>
<TR>
<TH VALIGN=TOP>
<TT><B>?</B></TT>
</TH>
<TD VALIGN=TOP>
None or one of the preceding ("<TT>words?</TT>" will match
"<TT>word</TT>" and "<TT>words</TT>".<BR> "<TT>[abc]?</TT>"
matches a single "<TT>a</TT>" <U>or</U> "<TT>b</TT>" <U>or</U>
"<TT>c</TT>" <U>or</U> nothing (i.e. "")).
</TD>
</TR>
<TR>
<TH VALIGN=TOP>
<TT><B>*</B></TT>
</TH>
<TD VALIGN=TOP>
None or more of the preceding ("<TT>words*</TT>" will match
"<TT>word</TT>", "<TT>words</TT>" and
"<TT>wordsssssss</TT>". "<TT>.*</TT>" will match anything
including nothing).
</TD>
</TR>
<TR>
<TH VALIGN=TOP>
<TT><B>+</B></TT>
</TH>
<TD VALIGN=TOP>
One or more of the preceding ("<TT>xxx+</TT>" will match a
sequence of 3 or more "<TT>x</TT>").
</TD>
</TR>
<TR>
<TH VALIGN=TOP>
<TT><B>(expr1|expr2)</B></TT>
</TH>
<TD VALIGN=TOP>
One of the expressions, which in turn may contain a similar
construction ("<TT>(foo|bar)</TT>" will match "<TT>foo</TT>"
<U>or</U> "<TT>bar</TT>".<BR> "<TT>(foo|bar)?</TT> will match
"<TT>foo</TT>" <U>or</U> "<TT>bar</TT>" <U>or</U> nothing
(i.e. "")).
</TD>
</TR>
<TR>
<TH VALIGN=TOP>
<TT><B>$</B></TT>
</TH>
<TD VALIGN=TOP>
The end of the line ("<TT>(foo|bar)$</TT>" will match
"<TT>foo</TT>" <U>or</U> "<TT>bar</TT>"only at the end of a
line).
</TD>
</TR>
<TR>
<TH VALIGN=TOP>
<TT><B>\<I>x</I></B></TT>
</TH>
<TD VALIGN=TOP>
Disable the special meaning of <TT><B><I>x</I></B></TT> where
<TT><B><I>x</I></B></TT> is one of the special regex characters
"<TT><B>.?*+()^$[]{}\</B></TT>" ("<TT>\.</TT>" will match a
single "<TT>.</TT>", "<TT>\\</TT>" a single "<TT>\</TT>" etc.)
</TD>
</TR>
</TABLE>
<br><br>
The entries to the expression lists are cleartext. Thus a start to block
possible sexual material by expression match could look like:
<br><br>
<table width="75%" cellpadding="0" cellspacing="0" style="background-color:
#f2fff0; border: solid 1px #4455bb;">
<tr>
<td>
<pre>
(^|[-\?+=/_])(bondage|boobs?|busty?|hardcore|porno?|sex|xxx+)([-\?+=/_]|$)
</pre>
</td></tr></table>
<br>
<br>
If everything is set up to your liking make the changes active by
issuing the command:<br><br>
<table width="75%" cellpadding="0" cellspacing="0" style="background-color:
#f2fff0; border: solid 1px #4455bb;">
<tr>
<td>
<pre>
squid -k reconfigure
</pre>
</td></tr></table>
<br>
<br>
<li><b>Some notes and hints</b>
<br><br>
<UL>
<LI>
Unless you build your expressions very very carefully there is a
high risk you will have annoyed users on your neck. Typically
you might accidentally block "Essex", "Sussex", "breastcancer",
"www.x.org" etc. in your eagerness for blocking pornographic
material. In practice you would probably replace some of the
words in the example above with some more clearly pornographic
related words that I don't find appropriate to list
here.<BR><BR>
</LI>
<LI>
While the size of the domain and urllists only has marginal
influence on the performance, too many large or complex
expressions will quickly degrade the performance of
squidGuard. Though it may depend heavily on the performance of
the regex library you link with.<BR><BR>
</LI>
<LI>
<A NAME="Sample adultdb"></A>There is a set of sample files
for a group of supposedly pornographic sites under
<TT>samples/dest/adult</TT> in the source tree that you can use as
a start if porn blocking is one of your tasks. <B>Please note:</B>
These lists are very, very old and not intended for production
systems. Use them to test your squidGuard. For an initial setup
the lists will work, but we recommend that you review these lists
before using them. Those
domains and urls have been collected <EM>automagically</EM> by a
robot. No manual evaluation of the corresponding contents has been
performed. Therefor there is a chance some nonpornographic sites
have sliped in. <br><br>
</LI>
<LI>
To avoid publishing to your users a complete guide to banned
sites, you probably want to have some or all of these files
protected by for instance:
<DL>
<DD>
<TT>
chmod 640 /<I>wherever</I>/filter/db/dest/adult/*<BR>
chown <I>cache_effective_user</I> /<I>wherever</I>/filter/db/dest/adult/*<BR>
chgrp <I>cache_effective_group</I> /<I>wherever</I>/filter/db/dest/adult/*
</TT>
</DD>
</DL>
where <TT>cache_effective_user</TT> and
<TT>cache_effective_group</TT> are the values for the
corresponding tags as defined in <TT>squid.conf</TT>.<BR>
</LI>
</UL>
</td></tr></table>
</td>
<td valign=top>
<br><br><br><br>
<a href="/Doc/index.html"><font color=black>Documentation</font></a>
<hr color="#001199">
<a href="/Doc/install.html"><font color=black>Installation</font></a>
<hr color="#001199">
Configuration</a>
<table border=0 cellspacing=1 cellpadding=1>
<tr><td> <a href="/Doc/configure.html"><font color=black size=-1>Getting started</font></a></td></tr>
<tr><td> <font size=-1>Destination ACLs</font></td></tr>
<tr><td> <font size=-1>Source ACLs</font></td></tr>
<tr><td> <a href="/Doc/redirect.html"><font color=black size=-1>Redirect Rule</font></a></td></tr>
<tr><td> <a href="/Doc/extended.html#times"><font color=black size=-1>Time Constraints</font></a></td></tr>
<tr><td> <a href="/Doc/authentication.html"><font color=black size=-1>Authentication</font></a></td></tr>
<tr><td> <a href="/Doc/expressionlist.html"><font color=black size=-1>Regular Expressions</font></a></td></tr>
<tr><td> <a href="/Doc/examples.html"><font color=black size=-1>Examples</font></a></td></tr>
</table>
<hr color="#001199">
<a href="runtimeops.html" target=body><font color=black>Runtime
Options</font></a>
<hr color="#001199">
<a href="aboutblocking.html"><font color=black>About blocking</font></a>
<hr color="#001199">
<a href="troubleshoot.html"><font color=black>Troubleshooting </font></a>
<hr color="#001199">
<a href="known_issues.html"><font color=black>Known Issues</font></a>
<hr color="#001199">
<a href="other_sources.html"><font color=black>Other Sources</font></a>
<hr color="#001199">
</td></tr>
</table>
<br><br>
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<font size=-2>
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Services</a> 2007-2008<br><br>
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