sub file2sha1 {
    my $file = $_[ 0 ];
    return '' if -d $file; #have to find out if to prune when a directory is found that doesn't match the regex
    open my $f, '<:raw', $file or do {
        warn "Cannot open '$file' $!";
        return;
        };
    my $sha1 = Digest::SHA1->new;
    $sha1->addfile( $f );
    return $sha1->digest;
}