Gnu screen in emacs shell mode: how to fix color escape codes

Question

I would like to attach screen or tmux inside emacs, in shell mode. I often find myself running emacs with inferior processes inside screen on remote servers; it would be nice if I could shift the workflow to local emacs + TRAMP; ability to reattach persistent sessions is a must, however. (Such workflow is particularly useful for analysis in R [1])

Shell-mode is rather desirable because I keep encountering miscellaneous glitches and even crashes when using the combination of M-x term or M-x ansi-term + screen + R. However, I can't seem to get rid of ansi colored rendered as escape codes in screen when run under M-x shell. When I use ansi-color-for-comint-mode-on, they are fine -- but as soon as screen comes on, it becomes a horrible mess.

Has anyone figured out the set of conditions for proper interpretation of ansi color with shell + screen or tmux? What about getting rid of color altogether?.. Are there any other alternatives in terms of running persistent remote processes and attaching them to local emacs?..

[1] http://blog.nguyenvq.com/2010/07/11/using-r-ess-remote-with-screen-in-emacs/

Answer 1

As far as I can tell, Screen requires features of your terminal that Emacs' shell mode simply does not and cannot provide, simply because it is not a traditional character terminal like VT100. So the issue is not about getting rid of or trying to interpret color codes -- there are more terminal capabilities that Screen requires to function correctly.

By default Screen does not even start in Emacs' shell mode, as far as I can tell (it errors out saying it needs clear screen capability). Some posts around the web seem to suggest setting TERM=xterm to work around this, but it is just fooling Screen into thinking the terminal has the capabilities of XTerm, which it doesn't have.

The term and ansi-term modes of Emacs would provide the terminal capabilities required by Screen, but unfortunately you seem to have had troubles with those modes.

What I would suggest instead would be to have a look at the "emacsclient -t" command (part of Emacs), which allows you to open a local frame connected to an existing Emacs instance in a similar way as Screen allows you to reconnect to a previously created Screen instance. That way you could perhaps configure a emacsclient on you local computer to reconnect over TCP to a persistent remote Emacs instance.

Answer 2

I don't use screen, but maybe you can fix this from your .bashrc. I've got a bunch of conditional code in there, turning color on for xterm windows, but leaving it off for other terminals that don't support it. M-x shell sets the TERM variable to dumb, so you can test for that and set the color accordingly.

case "$TERM" in
dumb)
## non-color settings here
;;
xterm)
## color settings here
;;
*)
## default (maybe you want non-color here?)
;;
esac