The ADD instruction is similar to the COPY instruction. However, in addition to the functionality supported by the COPY instruction, the ADD instruction can handle the TAR files and remote URLs. We can annotate the ADD instruction as COPY on steroids.
The following is the syntax of the ADD instruction:
ADD <src> ... <dst>
The arguments of the ADD instruction are very similar to those of the COPY instruction, as shown here:
- <src>: This is either the source directory or the file that is in the build context or in the directory from where the docker build subcommand will be invoked. However, the noteworthy difference is that the source can either be a TAR file stored in the build context or be a remote URL.
- ...: This indicates that multiple source files can either be specified directly or be specified using wildcards.
- <dst>: This is the destination path for the new image into which the source file or directory will be copied.
Here is an example for demonstrating the procedure for copying multiple source files to the various destination directories in the target image filesystem. In this example, we have taken a TAR file (web-page-config.tar) in the source build context with the http daemon configuration file and the files for the web pages are stored in the appropriate directory structure, as shown here:
$ tar tf web-page-config.tar
etc/httpd/conf/httpd.conf
var/www/html/index.html
var/www/html/aboutus.html
var/www/html/images/welcome.gif
var/www/html/images/banner.gif
The next line in the Dockerfile content has an ADD instruction for copying the TAR file (web-page-config.tar) to the target image and extracting the TAR file from the root directory (/) of the target image, as shown here:
ADD web-page-config.tar /
Thus, the TAR option of the ADD instruction can be used for copying multiple files to the target image.