How can you gain command line access in a running Docker container?

The most commonly used method to gain command line access in a running Docker container is through the command docker exec -it [container_id] /bin/bash. This command allows you to start a new interactive session inside the specified container.

The exec command is essential as it enables you to execute commands within an already running container. The -it flags are particularly important: -i stands for interactive and -t allocates a pseudo-TTY, allowing you to interact with the shell like you would in a normal command line interface. By specifying either /bin/bash or /bin/sh as the command to be executed inside the container, you determine which shell you want to use. The use of Bash is widespread because it offers more features than the basic shell (/bin/sh), including improved scripting capabilities, command history, and tab completion.

While other options presented may seem relevant, they either use incorrect commands or are not valid Docker syntax, such as the first option or the custom command in the third option, neither of which are valid for accessing a running container. The second option allows for shell access but specifies /bin/sh, which, while functional, doesn't leverage the advantages that Bash provides.