Shell Programming and Scripting

#!/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__

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+//;

open(CSV_FILE, '<', $csv_file) or die "Failed to read file $csv_file : $! \n";
# As long as the file didn't end, read a whole line to the variable $line
while (my $line = <CSV_FILE>) {
    # Skip this line unless it begins (^) with 3 digits (\d{3}), a dash, and
    # one or more digits (\d+) up to a ','
    next unless ($line =~ m/^\d{3}-\d+,/);
    # Split the line on the comma, assigning the fragments to the variables
    # in the order they occured
    my ($isbn, $title, $author, $category) = split(/,/, $line);
    # Compress whitespaces
    $title =~ s/^\s+//;
    $author =~ s/^\s+//;
    # Convert to lowercase
    $category = lc($category);
    $category =~ s/^\s+//;