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Re: Colored output

From: Jim Meyering
Subject: Re: Colored output
Date: Sun, 17 Mar 2019 11:24:21 -0700

On Sun, Mar 17, 2019 at 9:30 AM Bruno Haible <address@hidden> wrote:
> Hi Jim,
> You wrote in
> <https://lists.gnu.org/archive/html/bug-gnulib/2019-01/msg00173.html>:
> > I too would start with coreutils, noting that one must be careful to
> > handle signals, so that the terminal is not left in a bad state when
> > output is interrupted between a pair of set/reset escape sequences.
> > https://git.savannah.gnu.org/cgit/coreutils.git/tree/src/ls.c#n1303
> > Today I was surprised to see that while grep and recent diffutils also
> > have --color support, grep lacks the signal-handling code that is
> > present in both coreutils and diffutils.
> Thank you for mentioning the need for signal handling. I have implemented
> a reliable signal handling now, in libtextstyle-0.7:
>   https://alpha.gnu.org/gnu/gettext/libtextstyle-0.7.tar.gz
>   https://haible.de/bruno/gnu/libtextstyle-0.7.tar.gz
> And I am surprised to see that the color/signal handling in coreutils and
> diffutils, that you mention as starting points, implement only part of
> what is needed to make things reliable.
> In libtextstyle, I offer three levels of tty control to the application:
>   TTYCTL_NONE,      /* No control.
>                        Result: Garbled output can occur, and the terminal can
>                        be left in any state when the program is interrupted.  
> */
>   TTYCTL_PARTIAL,   /* Signal handling.
>                        Result: Garbled output can occur, but the terminal will
>                        be left in the default state when the program is
>                        interrupted.  */
>   TTYCTL_FULL       /* Signal handling and disabling echo and 
> flush-upon-signal.
>                        Result: No garbled output, and the the terminal will
>                        be left in the default state when the program is
>                        interrupted.  */
> TTYCTL_NONE is what 'grep' uses.
> TTYCTL_PARTIAL is what 'ls' and 'diff' use.
> TTYCTL_FULL is what libtextstyle offers by default, and is - in my testing -
> the only approach that does not produce garbled output.

Nice work!
Thank you for doing such a thorough job.

> 'ls' and 'diff' do not mitigate the problems (4) and (5).
> > If you factor some of that code into gnulib, that would be a fine
> > opportunity to use it to fix grep.
> Would you be prepared to use the 'term-ostream' module [1][2] in 'diff' and
> 'grep'?
> Or would it be better to separate the pure signal handling and tty cleanup
> code from the code that looks up the appropriate escape sequences from
> termlib/termcap, and create a module in gnulib with only the signal handling
> and tty cleanup code?

I'm happy to use whichever approach you prefer, especially if you
provide the patch.

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