I am trying to decode the value in "$data"

What you're trying to do is interpolate $data, or append it to $data_brf

Since single quotes do not interpolate, you get a literal $data instead of the contents of $data (interpolation)

As perlintro tells us, double quotes interpolate, so use double quotes

 $data_brf = "$data_dir\\$data\.brf";

 $data_brf = qq{$data_dir\\$data\.brf};

 $data_brf = qq[$data_dir\\$data\.brf];

 $data_brf = qq<$data_dir\\$data\.brf>;

 $data_brf = qq($data_dir\\$data\.brf);

 $data_brf = qq'$data_dir\\$data\.brf';