Others have pointed out some of the places where you have gone wrong in your original code. Here, I'd like to point out a recommended method from the FAQ.

If, for some odd reason, you really want to see the whole file at once rather than processing line-by-line, you can slurp it in (as long as you can fit the whole thing in memory!):

        open my $in,  '<',  $file      or die "Can't read old file: $!
+"
        open my $out, '>', "$file.new" or die "Can't write new file: $
+!";
        my $content = do { local $/; <$in> }; # slurp!
            # do your magic here
        print $out $content;
[download]

There really is lots of good stuff in the FAQ and if you will be doing any work with files at all, then FAQ 5 (linked above) will serve you well. Good luck.