
#!/usr/bin/perl

# This script will assume that the first command line argument
# is a file containing HTML, and return a version
# where all the tags are converted to lowercase.

use strict;
use warnings;

use HTML::Parser ();

HTML::Parser->new(
    start_h   => [\&start_lc,             "tokenpos, text"],
    end_h     => [sub { print lc shift }, "text"],
    default_h => [sub { print shift },    "text"],
)->parse_file(shift)
    || die "Can't open file: $!\n";

sub start_lc {
    my ($tpos, $text) = @_;
    for (my $i = 0; $i < @$tpos; $i += 2) {
        next if $i && ($i / 2) % 2 == 0;    # skip attribute values
        $_ = lc $_ for substr($text, $tpos->[$i], $tpos->[$i + 1]);
    }
    print $text;
}