Which command would you use to remove a directory that is not empty?

The command used to remove a directory that is not empty is "rm -r." This command leverages the recursive option, denoted by the -r (or --recursive) flag, which allows it to delete the directory along with all of its contents, including subdirectories and files. When working with directories in a Linux environment, it is important to note that the standard rmdir command can only remove empty directories. This limitation means that if you try to use rmdir on a directory that contains files or subdirectories, the command will fail with an error message.

The other options presented in the question serve different purposes. The tr command is a utility for translating or deleting characters from the input text, which does not relate to directory management. The updatedb command is used for updating the database used by the locate command to find files quickly; it does not have any functionality involving directory deletion. This further clarifies why "rm -r" is the correct choice for removing a non-empty directory in a Linux system.