my $fileHandle;  #Closes for you when it goes out of scope!
open $fileHandle, '>', $fileName or die "Can't open $fileName: $!\n";

writeFancyLogging($fileHandle, "Loggin' some stuff to a file");

sub writeFancyLogging
{
  my $file = shift;
  my $msg = shift;
  print $file $msg . "\n";
}