The docker container inspect command allows you to get detailed information about a container and its state:

$ docker container inspect --help

Usage:  docker container inspect [OPTIONS] CONTAINER [CONTAINER...]

Display detailed information on one or more containers

Options:
  -f, --format string   Format output using a custom template:
                        'json':             Print in JSON format
                        'TEMPLATE':         Print output using the given Go template.
                        Refer to https://docs.docker.com/go/formatting/ for more information about formatting output with templates
  -s, --size            Display total file sizes

The command provides information about the container identifier, the image information, the running status and exit code, the port mappings and bindings, the volumes and bind mount details, the network configuration, the environment variables, the metadata key-value pairs, the entry point and arguments, the CPU/memory limits and usage, the log driver configuration, the restart policy, the OS information, etc.

Let's run a container:

$ docker container run --rm -d --name "ubuntu-latest" ubuntu:latest sleep infinity

Let's inspect the container:

$ docker container inspect ubuntu-latest | jq

[
  {
    "Id": "8799a7ae86f491e2a1c8ec90ce0813322be327399cb59ecec3856b9de97570cb",
    "State": {
      "Status": "running"
    },
    "Image": "sha256:6015f66923d7afbc53558d7ccffd325d43b4e249f41a6e93eef074c9505d2233",
 ...
  }
]

The docker container exec command allow you to execute a command in a running container:

$ docker container exec --help

Usage:  docker container exec [OPTIONS] CONTAINER COMMAND [ARG...]

Execute a command in a running container

Aliases:
  docker container exec, docker exec

Options:
  -d, --detach               Detached mode: run command in the background
      --detach-keys string   Override the key sequence for detaching a container
  -e, --env list             Set environment variables
      --env-file list        Read in a file of environment variables
  -i, --interactive          Keep STDIN open even if not attached
      --privileged           Give extended privileges to the command
  -t, --tty                  Allocate a pseudo-TTY
  -u, --user string          Username or UID (format: "<name|uid>[:<group|gid>]")
  -w, --workdir string       Working directory inside the container

Let's check the running container:

$ docker container ls

CONTAINER ID   IMAGE           COMMAND            CREATED       STATUS       PORTS     NAMES
8799a7ae86f4   ubuntu:latest   "sleep infinity"   4 hours ago   Up 4 hours             ubuntu-latest

We can execute a specific commands (foreground) in the container:

$ docker container exec 8799a7ae86f4 id

uid=0(root) gid=0(root) groups=0(root)
$

$ docker container exec 8799a7ae86f4 cat /etc/hosts

127.0.0.1     localhost
172.17.0.2    ffd0458ac5e8
$

Using the pipe character (|) outside of the docker exec command causes the piping to occur on the host, not within the container. We can use the pipe character (|) to connect the output of one command to another, but be aware that the piping will occur on the host, not within the container. To perform piped operations within the container, wrap the full command in quotes and use /bin/bash -c:

$ docker container exec 8799a7ae86f4 /bin/bash -c "cat /etc/hosts | grep 127.0.0.1"

127.0.0.1    localhost
$

The same, if we want to run multiple commands inside the container:

$ docker container exec 8799a7ae86f4 /bin/bash -c "id; cat /etc/hosts | grep 127.0.0.1"

uid=0(root) gid=0(root) groups=0(root)
127.0.0.1    localhost
$

We can also exec in the container in an interactive mode by using the options -i (interactive session) and -t (pseudo-TTY):

$ docker container exec -it 8799a7ae86f4 /bin/bash

root@8799a7ae86f4:/# exit
exit
$