Introduction to Docker

The Docker COPY command is used in a Dockerfile to copy files or directories from the host machine into a container's filesystem. It allows you to include necessary files, such as application code or configuration files, during the image build process.

The syntax is:
COPY <src> <dest>,
where <src> is the path to the file on the host machine and <dest> is the destination path inside the container.

The COPY command is commonly used to add local files to Docker images, ensuring that the application has all the required resources when running in a container.

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The ADD and COPY commands in Docker are both used to copy files from the host system to a Docker container, but they have key differences:

- COPY: This command is used to copy files and directories from the host system into the container as-is. It’s simple and efficient for copying files without any additional processing.

- ADD: In addition to copying files, ADD can also automatically extract compressed tar files (e.g., .tar, .tar.gz) and can fetch files from URLs. However, due to these additional features, ADD is generally more powerful, but also less predictable and should be used cautiously.

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In summary, COPY is preferred for straightforward file copying, while ADD is used when you need to handle compressed files or download content from external sources.

In Docker, both COPY and ADD are used to copy files from the host machine into a container, but there are key differences:

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- COPY: It is a straightforward command that copies files or directories from the host to the container without any additional processing. It's typically used when you simply need to copy files as-is.

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- ADD: While it also copies files from the host to the container, ADD has additional functionality. It can automatically extract compressed tar files (e.g., .tar, .tar.gz), and it can also download files from URLs directly into the container. However, due to these extra features, ADD can sometimes be less predictable and should be used more selectively.

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In summary: Use COPY when you simply need to copy files, and use ADD when you need to handle compressed files or download content from a URL.