sub do_stuff {
    my $dir = shift;
    my $pattern = shift;
    ...


##</code><code>##

my ($dir, $pattern) = @_;


##</code><code>##

$what     --> $pattern_str
@t        --> @patterns
$f        --> $pattern 
$file2md5 --> $fname

##</code><code>##

"$file2md5"


##</code><code>##

my $fname_out = 'name.txt';

open my $OUTFILE, '>', $fname_out
  or die "Couldn't open $fname_out: $!";

#and then...
print $OUTFILE "whatever";