Docker Cookbook

34 | Chapter 1: Getting Started with Docker

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1.20 Copying Data to and from Containers
Problem
You have a running container started without any volume configuration, but you
would like to copy files in and out of the container.
Solution
Use the 
docker cp
command to copy files from a running container to the Docker
host. The 
docker cp
command allows you to copy files to and from the host to a con‐
tainer. The usage is as follows and is straightforward:
$ docker cp
docker: "cp" requires 2 arguments.
See 'docker cp --help'.
Usage: docker cp [OPTIONS] CONTAINER:PATH LOCALPATH|-
docker cp [OPTIONS] LOCALPATH|- CONTAINER:PATH
Copy files/folders between a container and your host.
...
Let’s illustrate this by first starting a container that will just sleep. You can enter the
container and create a file manually:
$ docker run -d --name testcopy ubuntu:14.04 sleep 360
$ docker exec -ti testcopy /bin/bash
root@b81793e9eb3e:/# cd /root
root@b81793e9eb3e:~# echo 'I am in the container' > file.txt
root@b81793e9eb3e:~# exit
Now to get the file that you just created in the container back in the host, 
docker cp
does the work:
$ docker cp testcopy:/root/file.txt .
$ cat file.txt
I am in the container
To copy from the host to the container, use 
docker cp
again but the other way
around:
$ echo 'I am in the host' > host.txt
$ docker cp host.txt testcopy:/root/host.txt
A nice use case is to copy from one container to another container, which is a matter
of combining the two methods by temporarily saving the files on the host. For exam‐
ple, if you want to transfer 
/root/file.txt
from two running containers with the names
c1
and 
c2
, use the following: