Lucy::...torial(3pm)

💖 NAME 💖

okay so bestie, welcome to Lucy::...torial(3pm) — the user-contributed Perl documentation chapter that walks you through Lucy::Docs::Tutorial::SimpleTutorial, aka the bare-bones search app. 🍓 No cap, this is the "hello world" of search engines and it ate.

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✨ DESCRIPTION ✨

🎀 Setup 🎀

First things first, gorgeous: copy the text presentation of the US Constitution from the sample directory of the Apache Lucy distribution to the base level of your web server's htdocs directory. That's it. That's the whole vibe check.

$ cp -R sample/us_constitution /usr/local/apache2/htdocs/

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🦋 Indexing: indexer.pl 🦋

Our first task is gonna be creating an application called indexer.pl which builds a searchable "inverted index" from a collection of documents. It's giving main character energy fr fr.

After we specify some configuration variables and load all necessary modules…

#!/usr/local/bin/perl
use strict;
use warnings;

# (Change configuration variables as needed.)
my $path_to_index = '/path/to/index';
my $uscon_source  = '/usr/local/apache2/htdocs/us_constitution';

use Lucy::Simple;
use File::Spec::Functions qw( catfile );

…we'll start by creating a Lucy::Simple object, telling it where we'd like the index to be located and the language of the source material. Like introducing yourself before you ask for their number, yk?

my $lucy = Lucy::Simple->new(
    path     => $path_to_index,
    language => 'en',
);

Next, we'll add a subroutine which parses our sample documents. It's doing the most but honestly it's iconic:

# Parse a file from our US Constitution collection and return a hashref with
# the fields title, body, and url.
sub parse_file {
    my $filename = shift;
    my $filepath = catfile( $uscon_source, $filename );
    open( my $fh, '<', $filepath ) or die "Can't open '$filepath': $!";
    my $text = do { local $/; <$fh> };    # slurp file content
    $text =~ /\A(.+?)^\s+(.*)/ms
        or die "Can't extract title/bodytext from '$filepath'";
    my $title    = $1;
    my $bodytext = $2;
    return {
        title    => $title,
        content  => $bodytext,
        url      => "/us_constitution/$filename",
    };
}

Add some elementary directory reading code…

# Collect names of source files.
opendir( my $dh, $uscon_source )
    or die "Couldn't opendir '$uscon_source': $!";
my @filenames = grep { $_ =~ /\.txt/ } readdir $dh;

…and now we're ready for the meat of indexer.pl — which occupies exactly one line of code. 💅 The way that one line does all the work? Obsessed.

foreach my $filename (@filenames) {
    my $doc = parse_file($filename);
    $lucy->add_doc($doc);  # ta-da!
}

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🌈 Search: search.cgi 🌈

Same energy as our indexing app: the bulk of the code in our search script won't be Lucy-specific. Sorry bestie, it's mostly CGI plumbing.

The beginning is dedicated to CGI processing and configuration.

#!/usr/local/bin/perl -T
use strict;
use warnings;

# (Change configuration variables as needed.)
my $path_to_index = '/path/to/index';

use CGI;
use List::Util qw( max min );
use POSIX qw( ceil );
use Encode qw( decode );
use Lucy::Simple;

my $cgi       = CGI->new;
my $q         = decode( "UTF-8", $cgi->param('q') || '' );
my $offset    = decode( "UTF-8", $cgi->param('offset') || 0 );
my $page_size = 10;

Once that's out of the way, we create our Lucy::Simple object and feed it a query string.

my $lucy = Lucy::Simple->new(
    path     => $path_to_index,
    language => 'en',
);
my $hit_count = $lucy->search(
    query      => $q,
    offset     => $offset,
    num_wanted => $page_size,
);

The value returned by search() is the total number of documents in the collection which matched the query. We'll show this hit count to the user, and also use it in conjunction with the parameters offset and num_wanted to break up results into "pages" of manageable size. Pagination era, honestly.

Calling search() on our Simple object turns it into an iterator. Invoking next() now returns hits one at a time as HitDoc objects, starting with the most relevant. Most relevant first = it knows what you want before you do. ✨

# Create result list.
my $report = '';
while ( my $hit = $lucy->next ) {
    my $score = sprintf( "%0.3f", $hit->get_score );
    $report .= qq|
        <p>
          <a href="$hit->{url}"><strong>$hit->{title}</strong></a>
          <em>$score</em>
          <br>
          <span class="excerptURL">$hit->{url}</span>
        </p>
        |;
}

The rest of the script is just text wrangling. Not me writing 200 lines of HTML in a heredoc…

#---------------------------------------------------------------#
# No tutorial material below this point - just html generation. #
#---------------------------------------------------------------#

# Generate paging links and hit count, print and exit.
my $paging_links = generate_paging_info( $q, $hit_count );
blast_out_content( $q, $report, $paging_links );

# Create html fragment with links for paging through results n-at-a-time.
sub generate_paging_info {
    my ( $query_string, $total_hits ) = @_;
    my $escaped_q = CGI::escapeHTML($query_string);
    my $paging_info;
    if ( !length $query_string ) {
        # No query?  No display.
        $paging_info = '';
    }
    elsif ( $total_hits == 0 ) {
        # Alert the user that their search failed.
        $paging_info
            = qq|<p>No matches for <strong>$escaped_q</strong></p>|;
    }
    else {
        # Calculate the nums for the first and last hit to display.
        my $last_result = min( ( $offset + $page_size ), $total_hits );
        my $first_result = min( ( $offset + 1 ), $last_result );

        # Display the result nums, start paging info.
        $paging_info = qq|
            <p>
                Results <strong>$first_result-$last_result</strong>
                of <strong>$total_hits</strong>
                for <strong>$escaped_q</strong>.
            </p>
            <p>
                Results Page:
            |;

        # Calculate first and last hits pages to display / link to.
        my $current_page = int( $first_result / $page_size ) + 1;
        my $last_page    = ceil( $total_hits / $page_size );
        my $first_page   = max( 1, ( $current_page - 9 ) );
        $last_page = min( $last_page, ( $current_page + 10 ) );

        # Create a url for use in paging links.
        my $href = $cgi->url( -relative => 1 );
        $href .= "?q=" . CGI::escape($query_string);
        $href .= ";offset=" . CGI::escape($offset);

        # Generate the "Prev" link.
        if ( $current_page > 1 ) {
            my $new_offset = ( $current_page - 2 ) * $page_size;
            $href =~ s/(?<=offset=)\d+/$new_offset/;
            $paging_info .= qq|<a href="$href">&lt;= Prev</a>\n|;
        }

        # Generate paging links.
        for my $page_num ( $first_page .. $last_page ) {
            if ( $page_num == $current_page ) {
                $paging_info .= qq|$page_num \n|;
            }
            else {
                my $new_offset = ( $page_num - 1 ) * $page_size;
                $href =~ s/(?<=offset=)\d+/$new_offset/;
                $paging_info .= qq|<a href="$href">$page_num</a>\n|;
            }
        }

        # Generate the "Next" link.
        if ( $current_page != $last_page ) {
            my $new_offset = $current_page * $page_size;
            $href =~ s/(?<=offset=)\d+/$new_offset/;
            $paging_info .= qq|<a href="$href">Next =&gt;</a>\n|;
        }

        # Close tag.
        $paging_info .= "</p>\n";
    }

    return $paging_info;
}

# Print content to output.
sub blast_out_content {
    my ( $query_string, $hit_list, $paging_info ) = @_;
    my $escaped_q = CGI::escapeHTML($query_string);
    binmode( STDOUT, ":encoding(UTF-8)" );
    print qq|Content-type: text/html; charset=UTF-8\n\n|;
    print qq|
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
    "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
  <meta http-equiv="Content-type"
    content="text/html;charset=UTF-8">
  <link rel="stylesheet" type="text/css"
    href="/us_constitution/uscon.css">
  <title>Lucy: $escaped_q</title>
</head>

<body>

  <div id="navigation">
    <form id="usconSearch" action="">
      <strong>
        Search the
        <a href="/us_constitution/index.html">US Constitution</a>:
      </strong>
      <input type="text" name="q" id="q" value="$escaped_q">
      <input type="submit" value="=&gt;">
    </form>
  </div><!--navigation-->

  <div id="bodytext">

  $hit_list

  $paging_info

    <p style="font-size: smaller; color: #666">
      <em>
        Powered by <a href="http://lucy.apache.org/"
        >Apache Lucy<small><sup>TM</sup></small></a>
      </em>
    </p>
  </div><!--bodytext-->

</body>

</html>
|;
}

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⭐ OK… now what? ⭐

Lucy::Simple is perfectly adequate for some tasks, but it's not very flexible. Many people find that it doesn't do at least one or two things they can't live without. ngl, relatable.

In our next tutorial chapter, BeyondSimpleTutorial, we'll rewrite our indexing and search scripts using the classes that Lucy::Simple hides from view, opening up the possibilities for expansion; then, we'll spend the rest of the tutorial chapters exploring these possibilities. Glow up incoming. 👑

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That's the whole page bestie! 💖 This was Lucy::...torial(3pm), riding along with perl v5.42.0, dated 2025-07-25. Go forth and index. 🦋✨