Piping a file into docker run

I need to pipe (inject) a file or some data into docker as part of the run command and have it written to a file within the container as part of the startup. Is there best practise way to do this ?

I've tried this.

cat data.txt |  docker run -a stdin -a stdout -i -t ubuntu /bin/bash -c 'cat >/data.txt'

But can't seem to get it to work.

cat setup.json |  docker run -i  ubuntu /bin/bash -c 'cat'

This worked for me. Remove the -t. Don't need the -a's either.

The better solution is to make (mount) you host folder be accessible to docker container. E.g. like this

docker run -v /Users/<path>:/<container path> ... 

Here is /Users/<path> is a folder on your host computer and <container path> mounted path inside container.

Also see Manage data in containers manual page.

UPDATE another Accessing External Files from Docker Containers example.