Dcycle Blog

Getting a Docker container's dynamic port on the command line

October 04, 2016

Generally I like to map my Docker containers to dynamic ports to avoid port collisions, so I’ll build my containers like this:

docker run --name some-container-name -d -p 80 some-image

Here, Docker will find a free port and map it to port 80 on the container.

Although not foolproof, the following code will tell you what that port is:

PORT="$(docker ps|grep some-container-name|sed \
  's/.*'|sed 's/->.*//g')"

And, if you’re using docker-compose, you can run, for example:

PORT=$(docker-compose port web 80)

This will give you something like