[Toybox] [PATCH] POSIX's unexpand command

[enh]

the BSD man page is (as so often) a lot less useless than the GNU one:
https://man.freebsd.org/cgi/man.cgi?query=unexpand

On Fri, Feb 23, 2024 at 6:27 PM Oliver Webb via Toybox
<toybox at lists.landley.net> wrote:
>
> Browsing through list archives from 2020, I found a mention of the unexpand command (in POSIX)
>
> From http://lists.landley.net/pipermail/toybox-landley.net/2020-May/019792.html:
>
> unexpand "converts spaces to tabs". Haven't gotten around to it yet. :)
>
> This commands behavior is so simple (s/  /\t/g) that it can be knocked out in a couple hours,
> The below patch is the command in 60 lines of code, and some tests for it.
>
> Since the command only looks for 2 characters (' ' and '\t'), no UTF safety checking is required,
> unexpand doesn't parse backspaces either.
>
> The only problem is...
>
> The GNU man page doesn't say if spaces are supposed to be processed beyond the beginning of lines.
> Since it specifies -a (Spaces -> tabs after the start of lines), and puts the option to disable that
> behavior under "--first-only" (while noting that it OVERRIDES -a). You would THINK it'd not process
> spaces like that, and the "--first-only" option serves the same purpose as grep -G (None at all, but might
> make option parsing a bit simpler for scripts).
>
> POSIX also doesn't make this apparent while also specifying -a, but in a much more verbose way because POSIX
>
> --first-only behavior is nice (the only reason I can find that would make this
> command more useful than sed 's/  /\t/g'), but long options are cumbersome.
>
> FAIL: unexpand -a behavior default
> echo -ne '  123  123\n' | "/sbin/unexpand" -t 2
> [...]
> -       123      123
> +       123       123
>
> Now it's converting spaces to tabs, while leaving trailing spaces?
>
> The man page does not document that:
>        -a, --all
>               convert all blanks, instead of just initial blanks
>
>        --first-only
>               convert only leading sequences of blanks (overrides -a)
>
>        -t, --tabs=N
>               have tabs N characters apart instead of 8 (enables -a)
>
> Also... why does -t enable -a, that makes doing testing on a terminal where tabs are displayed
> as 8 spaces a lot harder (have to switch on -t to make sure anything is being CONVERTED,
> but if you do that it will switch on another, completely unrelated option)...
>
> -   Oliver Webb <aquahobbyist at proton.me>_______________________________________________
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