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Do not use redirection characters in your shell prompt

(tanelpoder.com)
217 points tanelpoder | 1 comments | 17 Mar 21 14:38 UTC | HN request time: 0.232s | source
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jandrese ◴[17 Mar 21 15:32 UTC] No.26492618[source]▶
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.
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rcarmo ◴[17 Mar 21 15:42 UTC] No.26492739[source]▶
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.
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minitoar ◴[17 Mar 21 15:51 UTC] No.26492855[source]▶
Wow I never heard that! I always thought it was just some arbitrary convention I guess.
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taviso ◴[17 Mar 21 18:23 UTC] No.26494988[source]▶
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.

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1. kragen ◴[21 Mar 21 06:30 UTC] No.26528534[source]▶
Hmm, wasn't # the default erase character for teletype-era Unix? And @ the "kill" character (like modern ^U)? That would have made them a little annoying to type—not annoying enough to keep them from being used for cpp, though, and https://github.com/memnoth/unix-v6/blob/master/sys/dmr/tty.c... suggests that you could type \#. (There was no "lnext" yet; it was just hardcoded to backslash.)

The actual input erase handling is on https://github.com/memnoth/unix-v6/blob/master/sys/dmr/tty.c.... The relevant struct member is declared in https://github.com/memnoth/unix-v6/blob/master/sys/tty.h#L35 and initialized to CERASE in each tty driver, for example, https://github.com/memnoth/unix-v6/blob/master/sys/dmr/kl.c#..., using the macro defined in https://github.com/memnoth/unix-v6/blob/master/sys/tty.h#L48.

So by default # was special, just to the kernel tty driver, not the shell.