my %stopwd;
open( LIST, "my_stopwords.txt" ) or die "$!";
while (<LIST>) {
    chomp;
    $stopwd{$_} = undef;  # assume one word per line
}
close LIST;

# now, to remove stopwords, split the input data ($_) on \b
# and check each token:

my $filtered = join '', map { exists($stopwd{$_}) ? '':$_ } split /\b/;