How to Copy Files from Host to Docker Container

Docker is a platform used to develop, ship, and run applications inside containers. One of the common tasks when working with Docker is to transfer files between the host machine and the container. In this article, we will explore how to copy files from a host machine to a Docker container using the docker cp command.

Understanding the docker cp command

The docker cp command allows you to copy files or directories between a container and the local filesystem. The syntax is:

docker cp [OPTIONS] SRC_PATH CONTAINER:DEST_PATH

• SRC_PATH: This is the source file or directory on the host machine that you want to copy.
• CONTAINER: This is the name or ID of the Docker container to which you want to copy the file.
• DEST_PATH: This is the destination path inside the Docker container.

Copy files from Host to Docker Container

1. Before you can copy files to a container, find out the container name or id:

   docker ps 
   

2. If you want to copy a file named example.txt from your host machine to a container named mycontainer in the /tmp directory, you would use:

   docker cp example.txt mycontainer:/tmp/ 
   

3. To ensure that the file has been copied correctly, you can execute a command inside the container to check:

   docker exec mycontainer ls /tmp/ 
   

   You should see example.txt listed among the files in the /tmp/ directory.

Some Considerations

• Overwriting: The docker cp command can overwrite files inside the container without any warning. So always ensure the destination path is correct and doesn’t contain a file or directory with the same name, unless you intend to replace it.
• Permissions: Keep in mind that files copied to the container will maintain their permissions. Depending on your use case, you might need to adjust file permissions after copying them.
• Alternatives: Besides docker cp, you can also use volumes to share files between the host and containers. Volumes are a more advanced topic and are beneficial if you need to persist data or want real-time sync between the host and container filesystems.

Conclusion

Copying files between the host machine and Docker containers is a straightforward task when using the docker cp command. It’s a handy tool for managing files, especially for tasks like configuration or deploying application assets. Just always remember to double-check your source and destination paths and be mindful of file permissions.