Injecting a script to Pod with docker returns EOF - bash

Question

my goal is to execute a script once on a permanently running pod in kubernetes. The pod is called busybox-<SOME_ID> and finds itself in the namespace default.Therefore, I wrote this script - called scan-one-pod.sh:
#!/bin/bash
export MASTER_IP=192.168.56.102
export SCRIPT_NAME=script.sh
export POD_NAMESPACE=default
export POD_NAME=busybox
echo "echo HALLO" | ssh ubuntu#$MASTER_IP
export POD_ID=$(kubectl get po | grep busybox | sed -n '1p'|awk '{print $1}')
kubectl cp $SCRIPT_NAME $POD_NAMESPACE/$POD_ID:.
kubectl exec $POD_ID -- chmod +x $SCRIPT_NAME
export CONTAINER_ID=$(kubectl describe pod busybox | grep 'Container ID' | sed -n '1p'|awk '{print $3}')
ssh -t ubuntu#$MASTER_IP "sudo docker exec -u root $CONTAINER_ID -- ./script.sh"
The referred script script.sh has the following content:
$ kubectl exec $POD_ID -- cat script.sh
#!/bin/bash
echo "test" >> test
cp test test-is-working
However, it is not possible to run the script on the pod:
the files test and test-is-working are not created
the script scan-one-pod.sh returns just EOF:
$ ./scan-one-pod.sh
Pseudo-terminal will not be allocated because stdin is not a terminal.
Welcome to Ubuntu 16.04.3 LTS (GNU/Linux 4.4.0-87-generic x86_64)
* Documentation: https://help.ubuntu.com
* Management: https://landscape.canonical.com
* Support: https://ubuntu.com/advantage
155 Software-Pakete können aktualisiert werden.
72 Aktualisierungen sind Sicherheitsaktualisierungen.
HALLO
[sudo] Passwort für ubuntu:
EOF
Connection to 192.168.56.102 closed.
If I execute the docker-command directly, remote on my kubernetes-controller, I get the same message of EOF:
ubuntu#controller:~$ export CONTAINER_ID=$(kubectl describe pod busybox | grep 'Container ID' | sed -n '1p'|awk '{print $3}')
ubuntu#controller:~$ sudo docker exec -u root $CONTAINER_ID ./script.sh
EOF
If I execute it from my local workstation via kubectl exec I get this error:
$ kubectl exec $POD_ID ./script.sh
rpc error: code = 13 desc = invalid header field value "oci runtime error: exec failed: container_linux.go:247: starting container process caused \"no such file or directory\"\n"
I don't know, which missing file they are referring to, but the script.sh-file is present and the busybox-pod seems to be running:
$ kubectl exec $POD_ID ls script.sh
script.sh
$ kubectl get po busybox-6bdf9b5bbc-4skds
NAME READY STATUS RESTARTS AGE
busybox-6bdf9b5bbc-4skds 1/1 Running 10 12d
Question: As far as I know, EOF means End-Of-File. End of which file would be important for me to know, and why is that a problem?
Thanks in advance, any help is appreciated :)