# ...
open my $in, "<", "uuu.txt" or die "cannot open the input file$!";
open my $out, ">", "out.txt" or die "cannot open the output file$!";
while (my $line = <$in>) {
     $line =~s/[\s\d]//g;
     print $out "$line\n";
}
close $_ for ($in, $out);
# ... renaming, etc.