##
use IPC::Open2;
my($read_fh,$write_fh);
my $pid = open2($read_fh,$write_fh,"txt2html","--extract");
print $write_fh $plaintext;
close $write_fh;
my $html = do { local $/; <$read_fh> };
# or you can use a while(<$read_fh>) { ... } loop.
waitpid $pid, 0; # don't leave "zombies"