Wow; I had no idea Zsh printed out nonprintable characters that way. I
concur that it would make sense to change, modulo backward compatibility
considerations. Maybe a settable option?

 The M- "meta" syntax is something I associate with Emacs key-binding, and
have rarely seen in other contexts.

On Sun, Feb 25, 2024 at 4:08 AM Stephane Chazelas <stephane@chazelas.org>
wrote:

> I guess \M-^C (or \M-\C-C) as the representation of 0x83 made
> sense to people in the 80s/90s when they could actually type
> Meta-Ctrl-C on their keyboard to input them.
>
> Noaways, you can still enter ^C with Ctrl+C but bytes >= 0x80
> are used for non-ASCII characters, and Alt-C usually sends ^[c
> (0x1b 0x63) and Alt-Ctrl-C ^[^C (0x1b 0x3)
>
> I find the \x83 representation more useful when giving visual
> representations of bytes not forming part of a printable
> characters (and \uffff / \U0010ffff for valid but non-printable
> multi-byte characters). Octal used to be more popular than hex,
> but I think nowadays it's the reverse, though I still find \203
> more useful than \M-^C if not \x83.
>
> What do people think?
>
> Would it make sense to change some of the output intended for
> user consumption such as:
>
> $ a=$'\x83'
> $ typeset a
> a=$'\M-\C-C'
> $ print -r ${(q+)a}
> $'\M-\C-C'
> $ (set -x; : $a)
> +/bin/zsh:29> : $'\M-\C-C'
>
>
> $ let $a
> zsh: bad math expression: illegal character: \M-C
> $ let 1+$a
> zsh: bad math expression: operand expected at `\M-^C'
>
> (another M-C vs M-^C bug above by the way).
>
> Comparison with some other tools/shells:
>
> $ echo $a | cat -v
> M-^C
> $ echo $a | sed -n l
> \203$
> $ bash -xc 'printf "%q\n" "$a"'
> + printf '%q\n' $'\203'
> $'\203'
> $ ksh -xc 'printf "%q\n" "$a"'
> + printf '%q\n' $'\x83'
> $'\x83'
>
> --
> Stephane
>
>

-- 
Mark J. Reed <markjreed@gmail.com>