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Subject: |
tramp depends on unstable details of shell command line processing |
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Date: |
Sun, 2 Feb 2020 21:28:40 +0000 |
I use emacs tramp mode for remote editing. It stopped working on my FreeBSD
systems when I upgraded to a development version. The cause appears to be due
to /bin/sh reprinting the entire line when a backspace is sent rather than
sending only a backspace-space-backspace sequence. The failure follows a
change in the line editing library (shared with NetBSD) rather than the shell
itself.
Environment is emacs 24.5 or 26.3 running on Mac OS Catalina. The remote
system is FreeBSD 13.0 development. Tramp works with Linux or FreeBSD 12.1 as
the remote system.
Here's what happens.
I load tramp and open a file like /ssh:user@host:/. Emacs spawns ssh to
connect. The first thing tramp does is send
stty -inlcr -onlcr -echo kill '^U' erase '^H'
But this doesn't do much because the tty is in raw mode rather than cooked due
to the shell's line editor. So tramp falls back to a hack to detect echoed
input. It sends "_echo" followed by a string of backspace characters. "_echo"
is unlikely to appear in program output.
Here is the next command after the initial stty:
_echo^H^H^H^H^Hstty icanon erase ^H cols 32767_echo^H^H^H^H^H
The groups of 5 ^H represent 5 backspace characters and the lone ^H in the
middle is a two character sequence for stty.
The terminal output from a 12.1 system is
_echo^H ^H^H ^H^H ^H^H ^H^H ^Hstty icanon erase ^H cols 32767_echo^H ^H^H ^H^H
^H^H ^H^H ^H
#$
where again the middle ^H is a two character sequence and the others are
backspace characters. There is a carriage return between the two lines. "#$ "
is the shell prompt set by tramp.
The terminal output from a FreeBSD 13.0 development branch system is
_echo
#$ _ech ^H
#$ _ec ^H
#$ _e ^H
#$ _ ^H
#$ ^Hstty icanon erase ^H cols 32767_echo
#$ stty icanon erase ^H cols 32767_ech ^H
#$ stty icanon erase ^H cols 32767_ec ^H
#$ stty icanon erase ^H cols 32767_e ^H
#$ stty icanon erase ^H cols 32767_ ^H
#$ stty icanon erase ^H cols 32767 ^H
#$
with carriage returns between lines. This does not make sense to emacs, which
hangs waiting for something it recognizes. I can recover by hitting control-G
which aborts the tramp connection.
This issue is also reported to FreeBSD at
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=243807.
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--- Begin Message ---
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Subject: |
Re: bug#39399: tramp depends on unstable details of shell command line processing |
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Date: |
Tue, 28 Jul 2020 09:34:36 +0200 |
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User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux) |
内藤 祐一郎 <naito.yuichiro@gmail.com> writes:
Hi,
>> Appended is a patch for Tramp 2.4.4. You might install it from GNU
>> ELPA. Please check, whether this works for you.
>
> The appended patch works for me.
> But I think just moving "set +o emacs +o vi” before “stty …” is more simple
> way.
Thanks for the feedback. In fact, the patch does exactly this: moving up
the "set +o emacs +o vi” command. The rest of the patch removes the
handling of "~/.editrc", which was added as first attempt to solve this
bug, and which isn't needed anymore.
@John, I've Cc'ed you that you can check whether the changed fix still
works for you.
I'm closing this bug, again. The patch has been committed to the
repositories. Tramp 2.4.4.1, planned to be released later this week on
GNU ELPA, will contain it.
Furthermore, this patch will also be in Emacs 27.2. For Emacs 27.1 it's
too late to commit.
> Yuichiro NAITO
Best regards, Michael.
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