ISBN, Title, Category, cost, NO of copies
978-0340681138, Five Get into TRouble (Famous Five), Enid Blyton, Childrens, 6, 3
978-0142301883, The Little Match Girl, Hans Christian Anderson, Childrens, 3, 2
978-0304921532, cell, Stephen King, Horror, 7, 1
978-0596100292, Unix in a Nutshell Scripting, Arnold Robbins, Computing, 17, 2

ISBN: 978-0340681138
Author: Enid Blyton
Title: Five Get into Trouble (Famous Five)

#!/usr/bin/perl
# classify_books.pl
my $csv_file   = shift;
my %categories = ( 'childrens' => 'childrens_books.txt',
                   'horror'    => 'horror_books.txt',
                   'sports   ' => 'sports_books.txt',
                   'computing' => 'computing_books.txt');

my @childrens_file, @horror_file, @sports_file, @computing_file;

open(CSV_FILE, '<', $csv_file)  or  die "Failed to read file $csv_file : $! \n";
while (my $line = <CSV_FILE>) {
    next unless ($line =~ m/^\d{3}-\d+,/);
    my ($isbn, $title, $author, $category) = split(/,/, $line);
    $title    =~ s/^\s+//;
    $author   =~ s/^\s+//;
    $category = lc($category);
    $category =~ s/^\s+//;

    unless (exists($categories{$category})) {
        print STDERR "\nUndefined category $category for book $title by $author having ISBN $isbn \n";
        next;
    }

    if ($category =~ m/childrens/) {
        push(@childrens_file, "ISBN: $isbn\nAuthor: $author\nTitle: $title\n\n");
    }
    elsif ($category =~ m/horror/) {
        push(@horror_file, "ISBN: $isbn\nAuthor: $author\nTitle: $title\n\n");
    }
    elsif ($category =~ m/sports/) {
        push(@sports_file, "ISBN: $isbn\nAuthor: $author\nTitle: $title\n\n");
    }
    elsif ($category =~ m/computing/) {
        push(@computing_file, "ISBN: $isbn\nAuthor: $author\nTitle: $title\n\n");
    }
}
close(CSV_FILE);

if (@childrens_file) {
    open (CHL_FILE, '>', $categories{'childrens'})  or  die "Failed to write file $categories{'childrens'} : $! \n";
    print CHL_FILE @childrens_file;
    close (CHL_FILE);
}

if (@horror_file) {
    open (CHL_FILE, '>', $categories{'horror'})  or  die "Failed to write file $categories{'horror'} : $! \n";
    print CHL_FILE @horror_file;
    close (CHL_FILE);
}

if (@sports_file) {
    open (CHL_FILE, '>', $categories{'sports'})  or  die "Failed to write file $categories{'sports'} : $! \n";
    print CHL_FILE @sports_file;
    close (CHL_FILE);
}

if (@computing_file) {
    open (CHL_FILE, '>', $categories{'computing'})  or  die "Failed to write file $categories{'computing'} : $! \n";
    print CHL_FILE @computing_file;
    close (CHL_FILE);
}

__END__