What does the command `docker exec` accomplish?

The command docker exec is specifically designed to run a command in an already running container. This functionality allows users to interact with a container's environment, executing commands as if they were inside the shell of that container. This is particularly useful for debugging, monitoring, or administration purposes, as it provides the ability to launch a command-line interface (CLI) inside the container, without needing to stop it or create a new one.

For instance, if you want to check logs, modify configurations, or perform any other tasks that require access to the operational context of the running container, docker exec provides an efficient way to do so. It typically allows for the use of options, such as running commands in interactive mode or allocating a pseudo-TTY, which enhances the usability of terminal-based commands.

The other options represent different functionalities. Stopping a running container is managed by the docker stop command. Creating a new image is done through commands like docker build or docker commit, and listing all containers can be performed using docker ps or docker container ls. Each of these commands serves a distinct purpose within the Docker ecosystem, while docker exec focuses specifically on executing commands within existing, active containers.