WeeDie, did you try the solution provided by ikegami at the end of his post?

Then try substituting the find() call with the one in my post?

Please state how those solutions differ from your expectations.

The $fh_in and $fh_out are filehandle variables, much like MYFILE in your OP. Since you're new to Perl, you can think of those filehandle variables as another way to write GPXDATA and MYFILE, respectively.

Oh, and welcome to Perl! :)