/home/exit_status$ export PROMPT_COMMAND="echo $?"
0
/home/exit_status$ rm /
rm: cannot remove ‘/’: Is a directory
0
/home/exit_status$ echo $?
1
0

$ PROMPT_COMMAND="echo $?"
+ PROMPT_COMMAND='echo 0'
++ echo 0
0

$ PROMPT_COMMAND='echo $?'
+ PROMPT_COMMAND='echo $?'
++ echo 0
0

$ set +x
+ set +x
0
$ ls nofile
ls: cannot access 'nofile': No such file or directory
2

/home/exit_status$ export PROMPT_COMMAND="echo $?"
0
/home/exit_status$ rm /
rm: cannot remove ‘/’: Is a directory
0
/home/exit_status$ u=$?
0
/home/exit_status$ echo $u
1
0