How to edit Docker container files from the host?

We can use another way to edit files inside working containers (this won't work if container is stoped).

Logic is to:
-)copy file from container to host
-)edit file on host using its host editor
-)copy file back to container

We can do all this steps manualy, but i have written simple bash script to make this easy by one call.

/bin/dmcedit:

#!/bin/sh
set -e

CONTAINER=$1
FILEPATH=$2
BASE=$(basename $FILEPATH)
DIR=$(dirname $FILEPATH)
TMPDIR=/tmp/m_docker_$(date +%s)/

mkdir $TMPDIR
cd $TMPDIR
docker cp $CONTAINER:$FILEPATH ./$DIR
mcedit ./$FILEPATH
docker cp ./$FILEPATH $CONTAINER:$FILEPATH
rm -rf $TMPDIR

echo 'END'
exit 1;

Usage example:

dmcedit CONTAINERNAME /path/to/file/in/container

The script is very easy, but it's working fine for me.

Any suggestions are appreciated.

The best way is:

  $ docker cp CONTAINER:FILEPATH LOCALFILEPATH
  $ vi LOCALFILEPATH
  $ docker cp LOCALFILEPATH CONTAINER:FILEPATH

Limitations with $ docker exec: it can only attach to a running container.

Limitations with $ docker run: it will create a new container.

Whilst it is possible, and the other answers explain how, you should avoid editing files in the Union File System if you can.

Your definition of volumes isn't quite right - it's more about bypassing the Union File System than exposing files on the host. For example, if I do:

$ docker run --name="test" -v /volume-test debian echo "test"

The directory /volume-test inside the container will not be part of the Union File System and instead will exist somewhere on the host. I haven't specified where on the host, as I may not care - I'm not exposing host files, just creating a directory that is shareable between containers and the host. You can find out exactly where it is on the host with:

$ docker inspect -f "{{.Volumes}}" test
map[/volume_test:/var/lib/docker/vfs/dir/b7fff1922e25f0df949e650dfa885dbc304d9d213f703250cf5857446d104895]

If you really need to just make a quick edit to a file to test something, either use docker exec to get a shell in the container and edit directly, or use docker cp to copy the file out, edit on the host and copy back in.