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+#!/usr/bin/env perl
+#
+# Create a script to implement full text search functionality using Inverted
+# Index. According to wikipedia:
+#
+# In computer science, an inverted index (also referred to as a postings file or
+# inverted file) is a database index storing a mapping from content, such as
+# words or numbers, to its locations in a table, or in a document or a set of
+# documents (named in contrast to a forward index, which maps from documents to
+# content). The purpose of an inverted index is to allow fast full-text
+# searches, at a cost of increased processing when a document is added to the
+# database.
+#
+# Here is a nice example of Inverted Index.
+#
+# (https://en.wikipedia.org/wiki/Search_engine_indexing#Inverted_indices).
+################################################################################
+
+use strict;
+use warnings;
+
+use autodie;
+
+use DBI;
+
+my $DBFILE = 'ii.db';
+my $USAGE = "Usage: $0 [--index-doc <doc_path> | --search <word>]\n";
+
+my $opt = shift or die $USAGE;
+
+# Connect to database
+my $dbh = DBI->connect("dbi:SQLite:dbname=$DBFILE","","", { AutoCommit => 0 });
+
+# Initialize database
+$dbh->prepare('CREATE TABLE IF NOT EXISTS ii (word TEXT, docpath TEXT, PRIMARY KEY (word, docpath));')
+    ->execute();
+$dbh->prepare('CREATE INDEX IF NOT EXISTS word_idx ON ii (word);')
+    ->execute();
+$dbh->commit();
+
+if ($opt eq '--index-doc') {
+    # Index the given document
+    my $doc_path = shift;
+    open(my $dh, '<:encoding(UTF-8)', $doc_path);
+    $/ = undef;
+    my @words = map { lc($_) } <$dh> =~ /(\w+)/g;
+    my $sth = $dbh->prepare("INSERT OR IGNORE INTO ii VALUES (?, \"$doc_path\");");
+    $sth->execute($_) foreach @words;
+    $dbh->commit();
+} elsif ($opt eq '--search') {
+    # Search the given word
+    my $word = shift;
+    my $sth = $dbh->prepare('SELECT DISTINCT docpath FROM ii WHERE word = ?');
+    $sth->execute($word);
+    my @files = map { $_->[0] } @{$sth->fetchall_arrayref()};
+    if (@files) {
+        printf "Word '$word' appears in documents: %s\n", join(', ', @files);
+    } else {
+        print "Word '$word' does not appear in any document\n";
+    }
+} else {
+    die $USAGE;
+}
+
+$dbh->disconnect();