apt colored output (was Re: Buster => Bullseye: packages kept back)

[davidson <davidson@freevolt.org>]

On Tue, 28 Mar 2023 davidson wrote:

Replying to myself.

> According to [console_codes(4), under section ECMA-48 Set Graphics
> Rendition], [this value] sets "blink off"
>
> # apt -o "APT::Color::Highlight=^[[25m" search nethack
>
> For me, this produces text in the default style (no highlights, no
> colors).

This surprised me.

But it should not have, since the config option specified above just
tells apt to prefix the package name with a different PRETTIFY escape
sequence in output like

  <PRETTIFY>slashem-x11<RESET ATTRIBS>/stable 0.0.7E7F3-10 amd64
    variant of Nethack (X11 window port)

One that happens to set the blink display attribute off. Vacuously, of
course, unless you happen to have "blink on" set.

Might as well replace 25 ("blink off") with any of

  22        set normal intensity
  24        underline off
  25        blink off
  27        reverse video off

or just

  0         reset all attributes to their defaults

or nothing at all, ie

 APT::Color::Highlight=^[[m

which is equivalent to

 APT::Color::Highlight=^[[0m # reset all attributes to their defaults

This solves the problem of undesired colors, but not the emission of
unwanted escape sequences. And so there are bug reports like this:

  #1010806 - apt: Avoid color output on monochrome terminals
  https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1010806

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