[PATCH] termios.3: Clarify ONLRET

[PATCH] termios.3: Clarify ONLRET

[Simon Branch]

While perusing various termios(3) and termios(4) manpages, I noticed the
following inconsistency for ONLRET.  FreeBSD and NetBSD say this:

   If ONLRET is set, the NL character is assumed to do the carriage-return
   function; the column pointer will be set to 0.

OpenBSD says this:

   If ONLRET is set, NL also performs CR on output, and reset current column
   to 0.

POSIX says this:

   NL performs CR function.

The current Linux manpage says this (!):

   Don't output CR.

Here's a snippet that demonstrates Linux's behavior (tl;dr it's just like the
other operating systems):

   $ stty -icanon -onlcr -icrnl -echo onlret onocr; cat
   this is some text			(^J pressed)
                    and some more	(^M pressed before additional text)

The first flags (-icanon -onlcr -icrnl -echo), combined with cat, ensure that
our keys are sent directly back to the terminal emulator without any translation
or buffering.  The last two (ONLRET and ONOCR) are the important ones: ONLRET
makes Linux think that the cursor is at column 0 after the ^J, and ONOCR makes
Linux ignore the following ^M.

---
 man3/termios.3 | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/man3/termios.3 b/man3/termios.3
index c11937458..20641f14d 100644
--- a/man3/termios.3
+++ b/man3/termios.3
@@ -203,7 +203,9 @@ Map CR to NL on output.
 Don't output CR at column 0.
 .TP
 .B ONLRET
-Don't output CR.
+The NL character is assumed to do the carriage-return function;
+the kernel's idea of the current column is set to 0
+after both NL and CR.
 .TP
 .B OFILL
 Send fill characters for a delay, rather than using a timed delay.
-- 
2.34.0

---
 man3/termios.3 | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/man3/termios.3 b/man3/termios.3
index c11937458..20641f14d 100644
--- a/man3/termios.3
+++ b/man3/termios.3
@@ -203,7 +203,9 @@ Map CR to NL on output.
 Don't output CR at column 0.
 .TP
 .B ONLRET
-Don't output CR.
+The NL character is assumed to do the carriage-return function;
+the kernel's idea of the current column is set to 0
+after both NL and CR.
 .TP
 .B OFILL
 Send fill characters for a delay, rather than using a timed delay.
-- 
2.34.1

Re: [PATCH] termios.3: Clarify ONLRET

[Alejandro Colomar (man-pages)]

Hello Simon,

On 1/1/22 23:55, Simon Branch wrote:
> While perusing various termios(3) and termios(4) manpages, I noticed the
> following inconsistency for ONLRET.  FreeBSD and NetBSD say this:
> 
>    If ONLRET is set, the NL character is assumed to do the carriage-return
>    function; the column pointer will be set to 0.
> 
> OpenBSD says this:
> 
>    If ONLRET is set, NL also performs CR on output, and reset current column
>    to 0.
> 
> POSIX says this:
> 
>    NL performs CR function.
> 
> The current Linux manpage says this (!):
> 
>    Don't output CR.
> 
> Here's a snippet that demonstrates Linux's behavior (tl;dr it's just like the
> other operating systems):
> 
>    $ stty -icanon -onlcr -icrnl -echo onlret onocr; cat
>    this is some text			(^J pressed)
>                     and some more	(^M pressed before additional text)
> 
> The first flags (-icanon -onlcr -icrnl -echo), combined with cat, ensure that
> our keys are sent directly back to the terminal emulator without any translation
> or buffering.  The last two (ONLRET and ONOCR) are the important ones: ONLRET
> makes Linux think that the cursor is at column 0 after the ^J, and ONOCR makes
> Linux ignore the following ^M.
> 
> ---

Thanks for the patch!
I applied it, and signed it for you.

<http://www.alejandro-colomar.es/src/alx/linux/man-pages/man-pages.git/commit/?id=958604aae25a096d2c28410633af04a8bd068a73>

Cheers,

Alex

>  man3/termios.3 | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/man3/termios.3 b/man3/termios.3
> index c11937458..20641f14d 100644
> --- a/man3/termios.3
> +++ b/man3/termios.3
> @@ -203,7 +203,9 @@ Map CR to NL on output.
>  Don't output CR at column 0.
>  .TP
>  .B ONLRET
> -Don't output CR.
> +The NL character is assumed to do the carriage-return function;
> +the kernel's idea of the current column is set to 0
> +after both NL and CR.
>  .TP
>  .B OFILL
>  Send fill characters for a delay, rather than using a timed delay.

-- 
Alejandro Colomar
Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/
http://www.alejandro-colomar.es/