How to copy host files to docker

Today, the use of Docker in software development has become mainstream because it can quickly build, deploy and manage applications. Docker is widely used to create and run containers due to its portability and lightweight features. However, many people may encounter some problems when working with files in Docker. This article will teach you how to easily copy files on the host to Docker.

How to copy files in Docker

To copy files from the host to Docker, we can use the command that comes with Docker: docker cp. This command can copy a file or directory from the host to a running Docker container, or copy a file from a running Docker container to the host.

The syntax is as follows:

docker cp <src_path> <container_id>:<dest_path>

This command is very simple, among which:

• <src_path>: The file or folder to be copied path
• <container_id>: The ID of the Docker container
• <dest_path>: The destination path in the Docker container to copy to

For example, if you want to copy the myfile.txt file in the current directory to /app# of the Docker container named mycontainer ## directory, you can do as follows:

docker cp myfile.txt mycontainer:/app

This command copies the

myfile.txt file to the of the Docker container named mycontainer /app directory.

To copy the files in the Docker container back to the host, we can use a similar command:

docker cp <container_id>:<src_path> <dest_path>

Where:

• <container_id> : The ID of the Docker container
• <src_path>: The path of the file or folder to be copied
• <dest_path> : The target path in the host machine to be copied to

For example, if you want to copy

/app/myfile.txt# in the Docker container named mycontainer ## Copy the file to the ~/Downloads directory of the host. You can operate as follows: <pre class="brush:php;toolbar:false">docker cp mycontainer:/app/myfile.txt ~/Downloads</pre>This command will

mycontainer

in the container. The /app/myfile.txt file is copied to the ~/Downloads directory on the host machine. How to copy files in Dockerfile

The above method requires manually executing the command after starting the Docker container, but what if you want to automatically copy files to the container when creating the Docker image? Don’t worry, we can achieve this using the

COPY

command in the Dockerfile.

COPY

The command syntax is as follows:

COPY <src_path> <dest_path>

Among them:

<src_path>

: the file to be copied Or the path of the folder
• <dest_path>
: The destination path in the Docker container to be copied to
• For example, the following is an official Python image based on Dockerfile, which copies the
requirements.txt

file in the current directory to the

/app directory in the container:

FROM python:3.9-slim-buster
WORKDIR /app
COPY requirements.txt /app
RUN pip install --no-cache-dir -r requirements.txt
COPY . /app
CMD [ "python", "./app.py" ]

In this Dockerfile, The COPY requirements.txt /app command copies the

requirements.txt file to the /app directory in the Docker container. The RUN command uses this file to install the necessary dependencies. The last COPY command copies the entire application into the container. Summary

In this article, we learned how to copy files in Docker. Using the

docker cp

command, we can copy files from the host to a running Docker container or from a container to the host. In addition, in the Dockerfile, we can use the

COPY command to implement automatic copying from the host to the container. I hope this article will be helpful to you and allow you to better manage and use Docker containers.

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