Do not use redirection characters in your shell prompt

This seems to be more of "don't paste garbage into a terminal, especially as root." With a sidenote that it might be safer if your custom application command interpreter didn't use > as the prompt character. I note that Bourne shell defaults to the safer % and # characters for the prompt. The # character for root is especially safe.

Yeah. About the only relevant bit is that root prompts tend to use # as part of their prompt precisely to inject a comment character in case of mis-quotes/pastes.

Wow I never heard that! I always thought it was just some arbitrary convention I guess.

I've heard this story before, but I don't think it's true.

I think the bourne shell copied # comments from csh, which had them first. When sh first implemented them, # comments only worked in scripts, not if you typed them at the shell (i.e. if isatty(0), then # wasn't special). The fact that the prompt came before comments, and that comments didn't work interactively really makes the story sound suspect!

I don't know the origin of # in csh, but I would guess it was chosen because it looks like a CPP directive.

Even if # isn't / wasn't special, it's still exceedingly unlikely to be a valid program name, nor is it likely for a valid program name to begin with #. The practical effect should be the same as it having been special.