mjhjmtu

I run some commands in parallel and I want to see their last output after all of them complete (in the scrollback of my terminal emulator). Here's my test script test.screen:

# 
screen -t A sh -c 'echo important info && sleep 2'

split
focus

# 
screen -t B sh -c 'echo another important info && sleep 5'

The launch command:

$ screen -c test.screen

Output:

[screen is terminating]
[il@reallin ~]$


 --
another important info





 1 B

One problem is: when the first sleep 2 completes, the printed message important info is erased. If I add zombie kr at the beginning, then screen does not exit at all. As a workaround the caller can wait for all screen processes to exit and then issue -X quit

The other problem: the caret does not move to the bottom when screen exits and the shell prompt overwrites some data. The workaround is to echo $LINES times.

If you do not want the screen to clear when exiting "screen", you should choose (or modify) a terminal description which does not switch to the alternate screen. That is the TERM value outside screen.

With xterm (and a few others such as PuTTY) you can configure the terminal to prevent using the alternate screen, but for most terminals which copy xterm's alternate screen feature, this is hard-coded, not configurable. So the terminal description is the place to start.

ncurses provides a terminal description "xterm1" which has the alternate screen suppressed (and seeing that it is in Debian, it's probably in derived distributions such as Ubuntu). For other systems, it depends. Here's a difference from infocmp:

comparing xterm1 to xterm. 
 comparing booleans. 
 comparing numbers. 
 comparing strings. 
 rmcup: NULL, 'E[?1049l'. 
 smcup: NULL, 'E[?1049h'.

The "screen" program also has its own variant of the alternate screen which is normally off:

 altscreen on|off
 If set to on, "alternate screen" support is enabled in virtual termi‐ 
 nals, just like in xterm. Initial setting is `off'. 

Further reading:

• Why doesn't the screen clear when running vi?

There's no good solution for a split screen region being cleared: zombie windows prevent screen from exiting. I had to add additional synchronization between the windows and the caller script and when they all die, I call screen -X quit explicitly.

The altscreen command had nothing to do with this. The cursor didn't move to the bottom, because my default /etc/screenrc was half-working: the host terminal altscreen feature was used, but the altscreen wasn't cleared before switching back. To make it work by default I copied /etc/screenrc from CentOS 7 and for my case I disabled the feature completely with termcapinfo * ti=:te=.

test.sh:

#!/bin/bash

# set -e

if [ "a" = "$1" ]; then
 # decrement file name towards zero, then kill screen
 set -e
 a=-1
 cd "$COUNTERDIR"

 while true; do
 for old in *; do
 new=$((old + a))
 done
 [ 0 -eq "$a" ] || 2>/dev/null mv ./$old ./$new && break
 done

 if [ 0 -eq "$new" ]; then
 screen -X quit
 fi
 exit
fi


NWINDOWS=2
COUNTERDIR=`mktemp -d`
touch "$COUNTERDIR/$NWINDOWS"

export COUNTERDIR

screen -c test.screen
rm -rf "$COUNTERDIR"

test.screen:

# do not use host terminal altscreen feature
termcapinfo * ti=:te=
# windows stay after command terminates
zombie kr

screen -t A sh -c 'for ((i=0; i<100; i++)); do echo important info $i; done && sleep 5; ./test.sh a'

split
focus

screen -t B sh -c 'for ((i=0; i<100; i++)); do echo another important info $i; done && sleep 2; ./test.sh a'