Yeah, but it's kind of a mess. You have multiple options when implementing it without a clear standard, and in practice, it's a lot trickier to make sure that a

Yeah, but it's kind of a mess. You have multiple options when implementing it without a clear standard, and in practice, it's a lot trickier to make sure that all of your code does this consistently than it is to simply use different file descriptors for different output types. And then if the user wants to debug their script, they need to know to pipe your command to `cat` or whatever to see what's actually getting passed through.