Docker moving files in and out container

# this works
docker exec -it container_name bash

# this works (typing and close with ctrl-d to EOF)
docker exec -i container_name "bash" "-c" "cat - > kel"

# this only works without -t
cat some.txt | docker exec -i container_name "bash" "-c" "cat - > kel"

# alternatively
docker cp some.txt container_name:/kel