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Images

Basic Dockerfile example​

LABEL maintainer="Yaroslav Grebnov" version="1.0"
FROM nginx:alpine
COPY nginx.conf /etc/nginx/nginx.conf

Use variables in Dockerfile​

Variables in Dockerfile to be used during image building

ARG

Not cached

Variables in Dockerfile to be used during container running

ENV

Cached

Variables in Dockerfile to be used during both, image building and container running

ARG var
ENV var=${var}

Variable expansion in Dockerfile

COPY {var,,}

Remove dangling images​

docker rmi $(docker image ls -f "dangling=true" -q)

Command explantion:

  • docker image ls lists images
  • -f stands for filter. So, -f "dangling=true" selects only the dangling images
  • -q stands for quiet, which means that only the images IDs (hashes) are returned
  • docker rmi removes a list of selected images