Quoth wren ng thornton
There was a discussion about this recently over on libraries@, IIRC. The short answer is that, at present, there is no function to give you $0. We'd like to add such a function, but it's not been done yet.
Part of the problem is that, as Alexey says, the first element of argv is just whatever is passed to exec, which is not guaranteed to be a complete path, a canonical path, or any other specific thing we'd desire. It's not at all straightforward to determine the actual location of the executable, especially not in a platform-independent manner. argv[0] can't be trusted, scanning through $PATH isn't guaranteed to find it (and even if you find something of the right name, it's not guaranteed to be the correct executable), etc etc.
This isn't your problem, though. I mean, if the proposed function is to return the path to the executable file, then indeed you have a big problem with argv[0]. argv[0] can be anything - or nothing (it can be a null string.) But if we've turned to the question of whether to return argv[0], that's much simpler: you don't need to consider why a programmer might want it. It's appalling to think that library developers would withhold access to standard POSIX 1003.1 features while they decide whether they approve of them. Donn