echo "hello 1"

exec 3>&1  # Open FD 3 as a duplicate of stdout (fd 1)
# Run ./build.sh but make sure it does not have FD 3 open and tee to FD 3
VARIABLE=$(echo "hello 2" 3>&- | tee /dev/fd/3)
exec 3>&-  # Close FD 3

echo "hello 3"