GNU bug report logs - #37564
[PATCH] don't export LINES and COLUMNS env vars in term to fix ncurses applications

Previous Next

Full log

Message #20 received at 37564 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Matthew Leach <matthew <at> mattleach.net>
Cc: 37564 <at> debbugs.gnu.org
Subject: Re: bug#37564: [PATCH] don't export LINES and COLUMNS env vars in
 term to fix ncurses applications
Date: Tue, 01 Oct 2019 21:58:25 +0300

> From: Matthew Leach <matthew <at> mattleach.net>
> Cc: 37564 <at> debbugs.gnu.org
> Date: Tue, 01 Oct 2019 19:33:39 +0100
> 
> >> I'm curious as to which programs you are referring? AFAIK, if a program
> >> tries to read the LINES and COLUMNS environment variables, using
> >> `getenv()', they don't exist.
> >
> > What makes you say that? 
> 
> If I run the C program in my previous post in an xterm and resize I get:
> 
> getenv: (null) (null)
> ioctl:  24 80
> getenv: (null) (null)
> ioctl:  42 169
> 
> You can see that doing getenv() on LINES and COLUMNS returns a null
> pointer.  I've tested this same behaviour on gnome-terminal and numerous
> other terminal emulators.

I simply tried "env | fgrep LINES" and I do see the variable, although
it wasn't there before I launched Emacs.  'env' is just another
program accessing the environment, right?  I have no idea why your
test program doesn't see that, but then I'm far from being an expert
on these issues.

> > Emacs exports these variables into the environment that is passed to
> > child subprocesses, so those subprocesses will definitely see them
> > using getenv.
> 
> I'm no expert on how these things work but it doesn't appear to be the
> way that it's done, on my machine anyway.  Perhaps there are programs
> that uses these variables on MacOS or Windows?

I tried the above on a Trisquel GNU/Windows machine, FWIW.

> I'm testing this on the latest Emacs Git version. I can see that
> window-adjust-process-window-size-function is used in term.el however,
> this doesn't appear to update the environment variables exported to the
> terminal process.

AFAIR, it's supposed to send the corresponding ioctl command, in
addition to setting LINES and COLUMNS.

> If I run the same program with term on Emacs git and
> resize I get:
> 
> getenv: 31 80
> ioctl:  30 89
> getenv: 31 80
> ioctl:  30 90
> getenv: 31 80
> ioctl:  30 91
> getenv: 31 80
> ioctl:  31 92
> getenv: 31 80
> ioctl:  31 93
> getenv: 31 80
> ioctl:  31 94
> ...
> 
> Notice that the values returned by getenv don't change.

Again, the "env | fgrep LINES" method does show the change when I
resize the window on the machine I tried this, so I'm unsure why you
don't see it.

> Given that this functionality is broken, I'm suggesting that we don't
> export the variables.

I don't agree that it's broken; it isn't for me.  I think someone who
understands more than I do about this stuff should chime in and
explain why we see such different results.

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.