docker inspect <container name or id> |grep MacAddress|tr -d ' ,"'|sort -u

or inside the container:

ifconfig -a

ifconfig is part of the 'net-tools' linux pkg and this is good way to enter the running container:

nsenter -t $(docker inspect --format '{{ .State.Pid }}' <container name or id> ) -m -u -i -n -p -w 

Use docker inspect to pull MacAddress and redirect the results to a file. For example, try this on a container named my-container. This uses range (from the Go template package) to find MacAddress:

docker inspect -f '{{range .NetworkSettings.Networks}}{{.MacAddress}}{{end}}' my-container > /path/file.txt

If that doesn't work, first try viewing the metadata available for my-container:

docker inspect my-container

Find MacAddress in those results. Then create a docker inspect command that uses the docker json template function to pull the value from that specific json path. The path to MacAddress may vary, so here's an example that instead uses Status:

docker inspect -f "{{json .State.Health.Status}}" my-container > /path/file.txt