Pipe command to docker container run via sshd

I'm setting up an environment for users to log in to a machine via ssh. When logging in a docker container is created on the fly and removed when the user logs out.

This works like a charm interactively but you can't send a command like ssh -p 222 [email protected] "echo bla" to it. All you get is a the input device is not a TTY

The current configuration is:

sshd_config:

Match Group *
    forceCommand sudo /usr/local/bin/docker_shell.sh

/usr/local/bin/docker_shell.sh:

#!/bin/sh

UID=`id -u`
GID=`id -g`

HOME=`getent passwd $USER | cut -d: -f6`

/usr/bin/docker run --rm -w /home/$USER -v $HOME:/home/$USER \
         -v /run/mysqld/mysqld.sock:/run/mysqld/mysqld.sock \
         --mount type=tmpfs,destination=/tmp,tmpfs-size=10240000,tmpfs-mode=1777 \
         --user $UID:$GID -ti localregistry/shell_custom:0.5

The Dockerfile for the shell_custom container is trivial:

FROM alpine:latest

RUN apk add --no-cache bash && \
    apk add --no-cache mysql-client

COPY bashrc /etc/profile

CMD ["/bin/bash", "--rcfile", "/etc/profile"]

Now how do I get around the "the input device is not a TTY" issue? Any hint?

Thanks

Ekkehard