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Searching One by One, Take Two?><html><head><title>Searching One by One, Take Two (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="ch12_01.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_03.htm"><img src="../gifs/txtnexta.gif" alt="Next" border="0" /></a></td></tr></table></div><hr align="left" width="515" /><h2 class="sect1">12.2. Searching One by One, Take Two</h2><p>The search engine we will create in this <a name="INDEX-2366" /> <a name="INDEX-2,367" /><a name="INDEX-2368" /> <a name="INDEX-2,369" />section is much improved. It no longerdepends on <tt class="command">fgrep</tt> to carry out the search, whichalso means that we no longer have to use the shell. And thus, we willnot run into an internal glob limit.</p><p>In addition, this application returns the matched content andhighlights the query, which makes it much more useful as well.</p><p>How does it work? It creates a list of all the HTML files in thespecified directory using Perl's own functions, and theniterates over each file searching for a line that contains a matchfor the query. All matches are stored in an array and are laterconverted to HTML.</p><p><a href="ch12_02.htm#ch12-33630">Example 12-2</a> contains the new program.</p><a name="ch12-33630" /><div class="example"><h4 class="objtitle">Example 12-2. grep_search2.cgi </h4><a name="INDEX-2370" /><a name="INDEX-2,371" /><blockquote><pre class="code">#!/usr/bin/perl -wTuse strict;use CGI;use CGIBook::Error;my $DOCUMENT_ROOT = $ENV{DOCUMENT_ROOT};my $VIRTUAL_PATH = "";my $q = new CGI;my $query = $q->param( "query" );if ( defined $query and length $query ) { error( $q, "Please specify a valid query!" );}$query = quotemeta( $query );my $results = search( $q, $query );print $q->header( "text/html" ), $q->start_html( "Simple Perl Search" ), $q->h1( "Search for: $query" ), $q->ul( $results || "No matches found" ), $q->end_html;sub search { my( $q, $query ) = @_; my( %matches, @files, @sorted_paths, $results ); local( *DIR, *FILE ); opendir DIR, $DOCUMENT_ROOT or error( $q, "Cannot access search dir!" ); @files = grep { -T "$DOCUMENT_ROOT/$_" } readdir DIR; close DIR; foreach ( @files ) { my $full_path = "$DOCUMENT_ROOT/$_"; open FILE, $full_path or error( $q, "Cannot process $file!" ); while ( <FILE> ) { if ( /$query/io ) { $_ = html_escape( $_ ); s|$query|<B>$query</B>|gio; push @{ $matches{$full_path}{content} }, $_; $matches{$full_path}{file} = $file; $matches{$full_path}{num_matches}++; } } close FILE; } @sorted_paths = sort { $matches{$b}{num_matches} <=> $matches{$a}{num_matches} || $a cmp $b } keys %matches; foreach $full_path ( @sorted_paths ) { my $file = $matches{$full_path}{file}; my $num_matches = $matches{$full_path}{num_matches}; my $link = $q->a( { -href => "$VIRTUAL_PATH/$file" }, $file ); my $content = join $q->br, @{ $matches{$full_path}{content} }; $results .= $q->p( $q->b( $link ) . " ($num_matches matches)" . $q->br . $content ); } return $results;}sub html_escape { my( $text ) = @_; $text =~ s/&/&amp;/g; $text =~ s/</&lt;/g; $text =~ s/>/&gt;/g;}<a name="INDEX-2372" /><a name="INDEX-2373" /></pre></blockquote></div><p>This program starts out like our previous example. Since we aresearching for the query without exposing it to the shell, we nolonger have to strip out any characters from the query. Instead weescape any characters that may be interpreted in a regular expressionby calling <a name="INDEX-2374" /><a name="INDEX-2375" />Perl's<tt class="function">quotemeta</tt> function.</p><p>The<tt class="function">opendir</tt><a name="INDEX-2376" /><a name="INDEX-2377" /> function opens the specifieddirectory and returns a handle that we can use to get a list of allthe files in that directory. It's a waste of time to searchthrough <a name="INDEX-2378" /><a name="INDEX-2379" /> <a name="INDEX-2,380" />binary files, such as sounds andimages, so we use Perl's <tt class="function">grep</tt> function(not to be confused with the Unix <tt class="command">grep</tt> and<tt class="command">fgrep</tt> applications) to filter them out.</p><p>In this context, the <tt class="command">grep</tt> function iterates over alist of filenames returned by <tt class="function">readdir</tt> -- setting <tt class="literal">$_</tt> for eachelement -- and evaluates the expression specified within thebraces, returning only the elements for which the expression is true.</p><p>We are using <tt class="function">readdir</tt> in an array context so thatwe can pass the list of all files in the directory to<tt class="function">grep</tt> for processing. But there is a problem withthis approach. The <tt class="function">readdir</tt> function simplyreturns the name of the file and not the full path, which means thatwe have to construct a full path before we can pass it to the<tt class="function">-T</tt><a name="INDEX-2381" /> <a name="INDEX-2,382" /><a name="INDEX-2383" /> operator. We use the<tt class="literal">$DOCUMENT_ROOT</tt><a name="INDEX-2384" /> variable to create the fullpath to the file.</p><p>The <tt class="function">-T</tt> operator returns true if the file is atext file. After <tt class="function">grep</tt> finishes processing allthe files, <tt class="literal">@files</tt> will contain a list of all thetext files.</p><p>We iterate through the <tt class="literal">@files</tt> array, setting<tt class="literal">$file</tt> to the current value each time through theloop. We proceed to open the file, making sure to return an error ifwe cannot open it, and iterate through it one line at a time.</p><p>The <tt class="literal">%matches</tt> hash contains three elements:<em class="emphasis">file</em> to store the name of the file,<em class="emphasis">num_matches</em> to store the number of matches, anda <em class="emphasis">content</em> array to hold all the lines containingmatches. We need the filename for output purposes.</p><p>We use a simple case-insensitive<a name="INDEX-2385" />regex to search for the query. The<tt class="literal">o</tt> option compiles the regex only once, whichgreatly improves the speed of the search. Note that this will causeproblems for scripts running under <em class="emphasis">mod_perl</em> orFastCGI, which we'll discuss later in <a href="ch17_01.htm">Chapter 17, "Efficiency and Optimization"</a>.</p><p>If the line contains a match, we escape characters that could bemistaken for HTML tags. We then bold the matched text, increment thematch counter by the number of matches, and push that line onto thatfile's content array.</p><p>After we have finished looking through the files, we sort the resultsby the number of matches found in decreasing order and thenalphabetically by path for those who have the same number of matches.</p><p>To generate our results, we walk through our sorted list. For eachfile, we create a link and display the number of matches and all thelines that matched the query. Since the content exists as individualelements in an array, we <em class="emphasis">join</em> all the elementstogether into one large string delimited by an HTML break tag.</p><p>Now, let us improve on this application a bit by allowing users tospecify regular expression searches. We will not present the entireapplication, since it is very similar to the one we have justcovered.</p><a name="ch12-1-fm2xml" /><div class="sect2"><h3 class="sect2">12.2.1. Regex-Based Search Engine</h3><p>By allowing users to <a name="INDEX-2386" /> <a name="INDEX-2,387" />specifyregular expressions in their search, we make the search engine muchmore powerful. For example, a user who wants to search for the recipefor Zwetschgendatschi (a Bavarian plum cake) from your onlinecollection, but is not sure of the exact spelling, could simply enter<em class="emphasis">Zwet.+?chi</em> to find it.</p><p>In order to implement this functionality, we have to add severalpieces to the search engine.</p><p>First, we need to modify the <a name="INDEX-2388" />HTML file to provide an option forthe user to turn the functionality on or off:</p><blockquote><pre class="code">Regex Searching: <INPUT TYPE="radio" NAME="regex" VALUE="on">On <INPUT TYPE="radio" NAME="regex" VALUE="off" CHECKED>Off</pre></blockquote><p>Then, we need to check for this value in the application and actaccordingly. Here is the beginning of the new search script:</p><blockquote><pre class="code">#!/usr/bin/perl -wTuse strict;my $q = new CGI;my $regex = $q->param( "regex" );my $query = $q->param( "query" );unless ( defined $query and length $query ) { error( $q, "Please specify a query!" );}if ( $regex eq "on" ) { eval { /$query/o }; error( $q, "Invalid Regex") if $@;}else { $query = quotemeta $query;}my $results = search( $q, $query );print $q->header( "text/html" ), $q->start_html( "Simple Perl Regex Search" ), $q->h1( "Search for: $query" ), $q->ul( $results || "No matches found" ), $q->end_html;..</pre></blockquote><p>The rest of the code remains the same. What we are doing differentlyhere is checking if the user chose the "regex" option andif so, evaluating the user-specified regex at runtime using the<tt class="function">eval</tt><a name="INDEX-2389" /><a name="INDEX-2390" /> function. We can checkto see whether the regex is invalid by looking at the value stored in<tt class="literal">$@</tt>. Perl sets this variable if there is an errorin the evaluated code. If the regex is valid, we can go ahead and useit directly, without quoting the specified metacharacters. If the"regex" option was not requested, we perform the searchas before.</p><p>As you can see, both of these applications are much improved over thefirst one, but neither one of them is perfect. Since both of them arebased on a linear search algorithm, the search process will be slowwhen dealing with directories that contain many files. They alsosearch only one directory. They could be modified to recurse downthrough subdirectories, but that would decrease the performance evenmore. In the next section, we will look at an index-based approachthat calls for creating a dictionary of relevant words in advance,and then searching it rather than the <a name="INDEX-2391" /> <a name="INDEX-2,392" /> <a name="INDEX-2,393" /> <a name="INDEX-2,394" />actual files.</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="ch12_01.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_03.htm"><img src="../gifs/txtnexta.gif" alt="Next" border="0" /></a></td></tr><tr><td width="172" valign="top" align="left">12. Searching the Web Server</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">12.3. Inverted Index Search</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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