I'm not an expert on Win32, or the Win32::Perms module you're using, but something like this should work:

$userPerm is your command line argument

my $flags = $folder_ace|$subfolder_ace, ACCESS_ALL
+OWED_ACE_TYPE, OBJECT_INHERIT_ACE | CONTAINER_INHERIT_ACE;
if($userPerm eq 'READ')
{
$flags |= READ;
}
elsif($userPerm eq 'WRITE')
{
$flags |= WRITE;
}

$perms->Add('MYDOMAIN\bloggJo', $flags);
[download]

I've kept this verbose for clarity.

Your basic problem is that 'constants' in Perl are actually calls to subroutines, which return a constant value. And as the 'READ' or 'WRITE' arguments from the command line are simply text strings, they aren't then interpreted as constants.

So you need to 'translate' the command line args into calls to the relevant perl 'constants'.