# all html files in one directory
my @files = glob 'path/to/dir/*.html'; 

##</code><code>##

# all html files in all (direct, slibling) subdirectoris in a directory
my @files = glob 'path/to/dir/*/*.html';

##</code><code>##

use File::Spec::Functions qw(rel2abs abs2rel);
my $txt = rel2abs(abs2rel($file, $htmlroot), $txtroot);  # relocate
$txt =~ s/\.html$/.txt/;  # extension