# Exitcode 0 (`` has no exitcode, but assignment has):
true;  a=``; echo $?
false; a=``; echo $?
true;  a=$(); echo $?
false; a=$(); echo $?
# Exitcode 2 (`cmd` expansion sets exitcode after assignment set it to 0):
true;  a=`exit 2`; echo $?
false; a=`exit 2`; echo $?
true;  a=$(exit 2); echo $?
false; a=$(exit 2); echo $?
# Exitcode 1 (redirect sets exitcode to 1 on error after them):
true;  a=`` >/does/not/exist; echo $?
false; a=`` >/does/not/exist; echo $?
true;  a=$() >/does/not/exist; echo $?
false; a=$() >/does/not/exist; echo $?
true;  a=`exit 2` >/does/not/exist; echo $?
false; a=`exit 2` >/does/not/exist; echo $?
true;  a=$(exit 2) >/does/not/exist; echo $?
false; a=$(exit 2) >/does/not/exist; echo $?
# ...and assignment still happens despite redirect error:
true;  a=$(echo b) >/does/not/exist; echo $?
echo "Done: a=$a"