In general, you're better off using Devel::CheckOS instead of looking directly at $^O.

Second, I recommend putting all your platform-specific code into platform-specific modules. So, for example ...

use Devel::CheckOS qw(os_is);

if(os_is('MSWin32')) {
  eval 'use MyApplication::Platform::Win32';
} elsif(os_is('MacOSX')) {
  eval 'use MyApplication::Platform::MacOSX';
} else {
  warn "not MSWin32 or MacOSX, falling back to defaults\n";
  eval 'use MyApplication::Platform::Default';
}
[download]

Your MyApplication::Platform::* modules should then export the same set of subroutines that wrap up the platform-spceific bits, so that the core of your application is exactly the same no matter what platform. For example, they could all export a subroutine check_dir_is_writeable, whose Windows implementation would look like:

use Win32::File;
use Win32::FileSecurity;
sub check_dir_is_writeable {
  my $http_rec_localdir = shift;
  my $attrib;
  Win32::File::GetAttributes($http_rec_localdir, $attrib);
  if ($attrib & (Win32::File::SYSTEM | Win32::File::HIDDEN))
    ...
}
[download]

and whose Mac OS X implementation is:

  sub check_dir_is_writeable {
    -d $_ && -w $_ && -x $_
  }
[download]

Your application then can just do this to have it work on either platform:

  if(check_dir_is_writeable($dir)) {
    # yay!
  } else {
    # ohnoes!
  }
[download]