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Searching the Web Server?><html><head><title>Searching the Web Server (CGI Programming with Perl)</title><link href="../style/style1.css" type="text/css" rel="stylesheet" /><meta name="DC.Creator" content="Scott Guelich, Gunther Birznieks and Shishir Gundavaram" /><meta scheme="MIME" content="text/xml" name="DC.Format" /><meta content="en-US" name="DC.Language" /><meta content="O'Reilly & Associates, Inc." name="DC.Publisher" /><meta scheme="ISBN" name="DC.Source" content="1565924193L" /><meta name="DC.Subject.Keyword" content="stuff" /><meta name="DC.Title" content="CGI Programming with Perl" /><meta content="Text.Monograph" name="DC.Type" /></head><body bgcolor="#ffffff"><img src="gifs/smbanner.gif" alt="Book Home" usemap="#banner-map" border="0" /><map name="banner-map"><area alt="CGI Programming with Perl" href="index.htm" coords="0,0,466,65" shape="rect" /><area alt="Search this book" href="jobjects/fsearch.htm" coords="467,0,514,18" shape="rect" /></map><div class="navbar"><table border="0" width="515"><tr><td width="172" valign="top" align="left"><a href="ch11_03.htm"><img src="../gifs/txtpreva.gif" alt="Previous" border="0" /></a></td><td width="171" valign="top" align="center"><a href="index.htm">CGI Programming with Perl</a></td><td width="172" valign="top" align="right"><a href="ch12_02.htm"><img src="../gifs/txtnexta.gif" alt="Next" border="0" /></a></td></tr></table></div><hr align="left" width="515" /><h1 class="chapter">Chapter 12. Searching the Web Server</h1><div class="htmltoc"><h4 class="tochead">Contents:</h4><p><a href="ch12_01.htm">Searching One by One</a><br><a href="ch12_02.htm">Searching One by One, Take Two</a><br><a href="ch12_03.htm">Inverted Index Search</a><br></p></div><p>Allowing users to search for specific information on your <a name="INDEX-2339" /><a name="INDEX-2340" /><a name="INDEX-2341" />web siteis a very important and useful feature, and one that can save themfrom potential frustration trying to locate particular documents. Theconcept behind creating a search application is rather trivial:accept a query from the user, check it against a set of documents,and return those that match the specified query. Unfortunately, thereare several issues that complicate the matter, the most significantof which is dealing with large document repositories. In such cases,it's not practical to search through each and every document ina linear fashion, much like searching for a needle in a haystack. Thesolution is to reduce the amount of data we need to search by doingsome of the work in advance.</p><p>This chapter will teach you how to implement different types ofsearch engines, ranging from the trivial, which search documents onthe fly, to the most complex, which are capable of intelligentsearches.</p><div class="sect1"><a name="ch12-30160" /><h2 class="sect1">12.1. Searching One by One</h2><p>The very first example that we will look at is rather trivial in thatit does not perform the actual search, but passes the <a name="INDEX-2342" /> <a name="INDEX-2,343" /><a name="INDEX-2344" /> <a name="INDEX-2,345" />query to the <tt class="command">fgrep</tt>command and processes the results.</p><p>Before we go any further, here's the HTML<a name="INDEX-2346" />form that we will use to get theinformation from the user:</p><blockquote><pre class="code"><HTML><HEAD> <TITLE>Simple 'Mindless' Search</TITLE></HEAD><BODY><H1>Are you ready to search?</H1><P><FORM ACTION="/cgi/grep_search1.cgi" METHOD="GET"><INPUT TYPE="text" NAME="query" SIZE="20"><INPUT TYPE="submit" VALUE="GO!"></FORM></BODY></HTML></pre></blockquote><p>As we mentioned above, the program is quite simple. It creates a pipeto the <tt class="command">fgrep</tt> command and passes it the query, aswell as options to perform <a name="INDEX-2347" />case-insensitive searches and toreturn the matching filenames without any text. The programbeautifies the output from <tt class="command">fgrep</tt> by converting itto an HTML document and returns it to the browser.</p><p><em class="emphasis">fgrep</em> returns the list of matched files in thefollowing format:</p><blockquote><pre class="code">/usr/local/apache/htdocs/how_to_script.html/usr/local/apache/htdocs/i_need_perl.html..</pre></blockquote><p>The program converts this to the following HTML list:</p><blockquote><pre class="code"><LI><A HREF="/how_to_script.html" >how_to_script.html</A></LI><LI><A HREF="/i_need_perl.html">i_need_perl.html</A></LI>..</pre></blockquote><p>Let's look at the program now, as shown in <a href="ch12_01.htm#ch12-36249">Example 12-1</a>.</p><a name="ch12-36249" /><div class="example"><h4 class="objtitle">Example 12-1. grep_search1.cgi </h4><a name="INDEX-2348" /><a name="INDEX-2,349" /><blockquote><pre class="code">#!/usr/bin/perl -wT# WARNING: This code has significant limitations; see descriptionuse strict;use CGI;use CGIBook::Error;# Make the environment safe to call fgrepBEGIN { $ENV{PATH} = "/bin:/usr/bin"; delete @ENV{ qw( IFS CDPATH ENV BASH_ENV ) };}my $FGREP = "/usr/local/bin/fgrep";my $DOCUMENT_ROOT = $ENV{DOCUMENT_ROOT};my $VIRTUAL_PATH = "";my $q = new CGI;my $query = $q->param( "query" );$query =~ s/[^\w ]//g;$query =~ /([\w ]+)/;$query = $1;if ( defined $query ) { error( $q, "Please specify a valid query!" );}my $results = search( $q, $query );print $q->header( "text/html" ), $q->start_html( "Simple Search with fgrep" ), $q->h1( "Search for: $query" ), $q->ul( $results || "No matches found" ), $q->end_html;sub search { my( $q, $query ) = @_; local *PIPE; my $matches = ""; open PIPE, "$FGREP -il '$query' $DOCUMENT_ROOT/* |" or die "Cannot open fgrep: $!"; while ( <PIPE> ) { chomp; s|.*/||; $matches .= $q->li( $q->a( { href => "$VIRTUAL_PATH/$_" }, $_ ) ); } close PIPE; return $matches;}</pre></blockquote></div><p>We initialize three globals -- <tt class="literal">$FGREP</tt>,<tt class="literal">$DOCUMENT_ROOT</tt>, and<tt class="literal">$VIRTUAL_PATH</tt> -- which store the path to the<tt class="command">fgrep</tt> binary, the search directory, and thevirtual path to that directory, respectively. If you do not want theprogram to search the web server's top-level documentdirectory, you should change <tt class="literal">$DOCUMENT_ROOT</tt> toreflect the full path of the directory where you want to enablesearches. If you do make such a change, you will also need to modify<tt class="literal">$VIRTUAL_PATH</tt> to reflect the URL path to thedirectory.</p><p>Because Perl will pass our <tt class="command">fgrep</tt> command through a<a name="INDEX-2350" /> <a name="INDEX-2,351" /><a name="INDEX-2352" />shell, we need to makesure that the query we send it is not going to cause any securityproblems. Let's decide to allow only "words"(represented in Perl as "a-z", "A-Z","0-9", and "_") and spaces in the search. Weproceed to strip out all characters other than words and spaces andpass the result through an additional <a name="INDEX-2353" />regular expression to<a name="INDEX-2354" />untaint it. We need to do this extrastep because, although we know the substitution really did make thedata safe, a substitution is not sufficient to untaint the data forPerl. We could have skipped the substitution and just performed theregular expression match, but it means that if someone entered aninvalid character, only that part of their query before the illegalcharacter would be included in the search. By doing the substitutionfirst, we can strip out illegal characters and perform a search oneverything else.</p><p>After all this, if the query is not provided or is empty, we call ourfamiliar <em class="emphasis">error</em> subroutine to notify the user ofthe error. We test whether it is defined first to avoid a warning forusing an undefined variable.</p><p>We open a <a name="INDEX-2355" />PIPE to the<em class="emphasis">fgrep</em> command for reading, which is the purposeof the trailing "|". Notice how the syntax is not muchdifferent from opening a file. If the pipe succeeds, we can go aheadand read the results from the pipe.</p><p>The <tt class="command">-il</tt><a name="INDEX-2356" /> <a name="INDEX-2,357" /><a name="INDEX-2358" /> options force<tt class="command">fgrep</tt> to perform case-insensitive searches andreturn the filenames (and not the matched lines). We make sure toquote the string in case the user is searching for a multiple wordquery.</p><p>Finally, the last argument to <em class="emphasis">fgrep</em> is a list ofall the files that it should search. The shell expands(<a name="INDEX-2359" /> <a name="INDEX-2,360" /><a name="INDEX-2361" />globs)the wildcard character into a list of all the files in the specifieddirectory. This can cause problems if the directory contains a largenumber of files, as some shells have internal glob limits. We willfix this problem in the next section.</p><p>The <tt class="function">while</tt> loop iterates through the results,setting <tt class="literal">$_</tt> to the current record each time throughthe loop. We strip the end-of-line character(s) and the directoryinformation so we are left with just the filename. Then we create alist item containing a hypertext link to the item.</p><p>Finally, we print out our results.</p><p>How would you rate this application? It's a simple searchengine and it works well on a small collection of files, but itsuffers from a few problems:</p><ul><li><p>It calls an external application (<tt class="command">fgrep</tt>) to handlethe search, which makes it nonportable; Windows 95 for instance doesnot have a <tt class="command">fgrep</tt> application.</p></li><li><p>Alphanumeric "symbols" are stripped from the searchquery, due to security concerns.</p></li><li><p>It could very well run into an internal glob limit when used withcertain shells; some shells have limits as low as 256 files.</p></li><li><p>It does not search multiple directories.</p></li><li><p>It does not return content, but simply filename(s), although we couldhave added this functionality by not specifying the<em class="emphasis">-l</em> option.</p></li></ul><p>So, let's try again and create a better search <a name="INDEX-2362" /> <a name="INDEX-2,363" /> <a name="INDEX-2,364" /> <a name="INDEX-2,365" />engine.</p></div><hr align="left" width="515" /><div class="navbar"><table border="0" width="515"><tr><td width="172" valign="top" align="left"><a href="ch11_03.htm"><img src="../gifs/txtpreva.gif" alt="Previous" border="0" /></a></td><td width="171" valign="top" align="center"><a href="index.htm"><img src="../gifs/txthome.gif" alt="Home" border="0" /></a></td><td width="172" valign="top" align="right"><a href="ch12_02.htm"><img src="../gifs/txtnexta.gif" alt="Next" border="0" /></a></td></tr><tr><td width="172" valign="top" align="left">11.3. Client-Side Cookies</td><td width="171" valign="top" align="center"><a href="index/index.htm"><img src="../gifs/index.gif" alt="Book Index" border="0" /></a></td><td width="172" valign="top" align="right">12.2. Searching One by One, Take Two</td></tr></table></div><hr align="left" width="515" /><img src="../gifs/navbar.gif" alt="Library Navigation Links" usemap="#library-map" border="0" /><p><font size="-1"><a href="copyrght.htm">Copyright © 2001</a> O'Reilly & Associates. 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