Did you actually open a file and assign the handle to $fh_in?

open(my $fh_in, '<', $qualified_name)
   or die("Unable to open file \"$qualified_name\" to split: $!\n");
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and what is $fh_out? $fh_in is the text file it is reading right?

Yes, except that these are "file handles" rather than the actual file in any sense, (hence the naming convention "fh").

Does that make sense? If you do a close $fh_out; the file doesn't go away, just perl's ability to write to the file via that particular handle.

Thanks for the explaination of file handler.. it make sense.. i did specified a fh_in. but i'm still not sure what does fh_out do? we have $base and $ext to work out the file name of the output so what does fh_out do?

Just as '$fh_in' is the file handle for input, '$fh_out' is the file handle for output. The print function checks its first argument (the first thing that comes after the word "print"), and if this arg turns out to be a file handle, then the rest of the args are printed to that file; if the first arg after "print" is not a file handle, then print assumes 'STDOUT' (the default output file handle) and prints all its args to that "file" (which is usually your terminal window).