sub openurl {
  my $url = shift;
  my $platform = $^O;
  my $cmd;
  if    ($platform eq 'darwin')  { $cmd = "open \"$url\"";       }  # OS X
  elsif ($platform eq 'MSWin32' or $platform eq 'msys') { $cmd = "start \"\" \"$url\""; } # Windows native or MSYS / Git Bash
  elsif ($platform eq 'cygwin')  { $cmd = "cmd.exe /c start \"\" \"$url \""; } # Cygwin; !! Note the required trailing space.
  else { $cmd = "xdg-open \"$url\""; }  # assume a Freedesktop-compliant OS, which includes many Linux distros, PC-BSD, OpenSolaris, ...
  if (system($cmd) != 0) {
    die "Cannot locate or failed to open default browser; please open '$url' manually.";
  }
}