In the context of what it seems to be primarily attempting to achieve, assisting in the bootstrapping of more complex environments directly or indirectly dependent on C, I found the base64 example (more so the SHA-256 example in the same directory) quite interesting and evidence of the sophistication of pnut notwithstanding the limitations. And as was pointed out, it wouldn't be difficult to hack in the ability to read binary data: just swap in a replacement for the getchar routine, such as I've done with od. In fact, that ease is one of the most fascinating aspects of this project--they've built a conceptually powerful execution model for the shell that can be directly targeted when compiling C code, as opposed to indirection through an intermediate VM (e.g. a P-code interpreter in shell). It has it's limitations, but those can be addressed. Given the constraints, the foundation is substantial and powerful even from a utilitarian perspective.

When people discuss Turing completeness and related concepts one of the unstated caveats is that neither the concept itself, nor most solutions or environments, meaningfully address the problem of I/O with the external environment. pnut is kind of exceptional in this regard, even with the limitations.