Dockerfile

FROM debian:bookworm-slim
RUN apt update && apt install -y lftp

Send from terminal

docker run -v $(pwd)/file_to_send:/tmp/file_to_send \
-p 2020:20/tcp -p 2121:21/tcp  --network host \
ftpdocker lftp ftp://user:123@localhost:21 \
-e "put /tmp/file_to_send; bye"

1. Mount file "file_to_send" to container /tmp/file_to_send
2. Run client on localhost network (2020 and 2021)
3. Execute lftp command with rmeote server URL, username & password
4. Send FTP command (file) and close