What is the difference between the 'COPY' and 'ADD' commands in a Dockerfile?

ghz 1years ago ⋅ 692 views

Question

What is the difference between the COPY and ADD commands in a Dockerfile, and when would I use one over the other?

COPY <src> <dest>

The COPY instruction will copy new files from <src> and add them to the container's filesystem at path <dest>

ADD <src> <dest>

The ADD instruction will copy new files from <src> and add them to the container's filesystem at path <dest>.

Answer

You should check the ADD and COPY documentation for a more detailed description of their behaviors, but in a nutshell, the major difference is that ADD can do more than COPY:

  • ADD allows <src> to be a URL
  • Referring to comments below, the ADD documentation states that:

If is a local tar archive in a recognized compression format (identity, gzip, bzip2 or xz) then it is unpacked as a directory. Resources from remote URLs are not decompressed.

Note that the [Best practices for writing Dockerfiles](https://docs.docker.com/develop/develop-images/instructions/#add- or-copy) suggests using COPY where the magic of ADD is not required. Otherwise, you ( since you had to look up this answer ) are likely to get surprised someday when you mean to copy keep_this_archive_intact.tar.gz into your container, but instead, you spray the contents onto your filesystem.

#docker