Copy files/folders between containers and the local filesystem.

Usage:  docker cp [options] CONTAINER:PATH LOCALPATH|-
        docker cp [options] LOCALPATH|- CONTAINER:PATH

--help  Print usage statement

In the first synopsis form, the docker cp utility copies the contents of
PATH from the filesystem of CONTAINER to the LOCALPATH (or stream as
a Tar Archive to STDOUT if - is specified).

In the second synopsis form, the contents of LOCALPATH (or a Tar Archive
streamed from STDIN if - is specified) are copied from the local machine to
PATH in the filesystem of CONTAINER.

You can copy to or from either a running or stopped container. The PATH can
be a file or directory. The docker cp command assumes all CONTAINER:PATH
values are relative to the / (root) directory of the container. This means
supplying the initial forward slash is optional; The command sees
compassionate_darwin:/tmp/foo/myfile.txt and
compassionate_darwin:tmp/foo/myfile.txt as identical. If a LOCALPATH value
is not absolute, is it considered relative to the current working directory.

Behavior is similar to the common Unix utility cp -a in that directories are
copied recursively and file mode, permission, and ownership are preserved if
possible.

Assuming a path separator of /, a first argument of SRC_PATH and second
argument of DST_PATH, the behavior is as follows:

• SRC_PATH specifies a file
  • DST_PATH does not exist
    • the file is saved to a file created at DST_PATH
  • DST_PATH does not exist and ends with /
    • Error condition: the destination directory must exist.
  • DST_PATH exists and is a file
    • the destination is overwritten with the contents of the source file
  • DST_PATH exists and is a directory
    • the file is copied into this directory using the basename from
      SRC_PATH
• SRC_PATH specifies a directory
  • DST_PATH does not exist
    • DST_PATH is created as a directory and the contents of the source
      directory are copied into this directory
  • DST_PATH exists and is a file
    • Error condition: cannot copy a directory to a file
  • DST_PATH exists and is a directory
    • SRC_PATH does not end with /.
      • the source directory is copied into this directory
    • SRC_PAPTH does end with /.
      • the content of the source directory is copied into this
        directory

The command requires SRC_PATH and DST_PATH to exist according to the above
rules. If SRC_PATH is a symbolic link, the symbolic link, not the target, is
copied. If a path separator immediately follows the symbolic link, it will be
resolved to its target and the target resource will be copied.

A colon (:) is used as a delimiter between CONTAINER and PATH, but :
could also be in a valid LOCALPATH, like file:name.txt. This ambiguity is
resolved by requiring a LOCALPATH with a : to be made explicit with a
relative or absolute path, for example:

`/path/to/file:name.txt` or `./file:name.txt`

It is not possible to copy certain system files such as resources under
/proc, /sys, /dev, and mounts created by the user in the container.

Using - as the first argument in place of a LOCALPATH will stream the
contents of STDIN as a Tar Archive which will be extracted to the PATH in
the filesystem of the destination container. In this case, PATH must specify
a directory.

Using - as the second argument in place of a LOCALPATH will stream the
contents of the resource from the source container as a Tar Archive to
STDOUT.

• replaces docker cp to, from, and between containers #10198
• fixes Moving a file from the host system to a container via docker cp #5846
• fixes docker cp should accept a file destination #4272
• fixes docker cp does not cause a conflict when the archived directory structure replaces a directory with a file or vice versa #10040