...
my $inputFile = q{C:/INPUTFILE};
open my $inputFH, q{<}, $inputFile
   or die qq{open: < $inputFile: $!\n};

my $outputFile = q{C:/OUTPUT.TXT};
open my $outputFH, q{>}, $outputFile
   or die qq{open: > $outputFile: $!\n};
...
    while( <$inputFH> )
...
    print $outputFH ...
...
close $inputFH or die qq{close: < $inputFile: $!\n};
close $outputFH or die qq{close: > $outputFile: $!\n};