What is Dockerfile heredoc syntax and when would you use it?

Dockerfile heredoc syntax (introduced in Dockerfile 1.4, enabled with BuildKit) allows writing multi-line strings directly in Dockerfile instructions without the awkward backslash-newline continuation. Two main uses: (1) Multi-line RUN scripts: instead of RUN command1 && \\n command2 && \\n command3, use: RUN <<EOF\ncommand1\ncommand2\ncommand3\nEOF. More readable, especially for complex shell scripts. Can specify the shell: RUN <<EOF bash\nset -e\napt-get update\napt-get install -y curl\nEOF; (2) Inline file creation: create configuration files directly in the Dockerfile instead of COPYing them from a separate file: COPY <<EOF /etc/nginx/conf.d/default.conf\nserver {\n listen 80;\n location / {\n proxy_pass http://app:3000;\n }\n}\nEOF. Also: RUN <<EOF python3\nimport os\nprint(os.environ.get("HOME"))\nEOF — run Python inline. Enable heredoc: add # syntax=docker/dockerfile:1 at the top of your Dockerfile (allows Dockerfile syntax versioning). Benefits: cleaner Dockerfiles, no need for separate config files that only exist for COPY, more readable multi-step commands.