Assemble a container image with buildah's scripted commands (no Dockerfile): buildah from scratch or a base image, then run, copy, config, and commit.

Documented steps

1. Create an empty working container: `newcontainer=$(buildah from scratch)` — 'scratch' tells Buildah to create an empty container with minimal metadata (tutorial docs/tutorials/01-intro.md). To base on an existing image instead: `container=$(buildah from fedora)`.
2. Verify with `buildah containers` (lists CONTAINER ID, IMAGE NAME, CONTAINER NAME e.g. 'working-container') and `buildah images`.
3. To manipulate the scratch container's filesystem directly, mount it: `scratchmnt=$(buildah mount $newcontainer)`. In rootless mode this fails unless you first enter a user/mount namespace with `buildah unshare`: `export newcontainer; buildah unshare` then run the mount inside that shell (tutorial 01-intro.md).
4. Populate content: install packages into the mount root, e.g. `dnf install --installroot $scratchmnt --releasever <ver> bash coreutils --use-host-config -y`, or copy files in with `buildah copy $newcontainer ./runecho.sh /usr/bin/` (buildah-copy: copies a file/URL/directory into the container).
5. Run commands inside the working container as build steps: `buildah run $newcontainer bash` or `buildah run $newcontainer -- dnf -y install java` (the `--` separates buildah's options from the command). Per docs/buildah-run.1.md, `buildah run` is analogous to a Dockerfile RUN instruction (unlike `podman run`, which is analogous to `docker run`).
6. Set image config metadata with `buildah config`: `buildah config --cmd /usr/bin/runecho.sh $newcontainer`, `buildah config --entrypoint '["command", "arg1"]' $newcontainer`, `buildah config -e KEY=value $newcontainer`, `buildah config -l name=value $newcontainer`, plus --author, --created-by, --port 80, --annotation key=value (docs/buildah-config.1.md).
7. Commit the container to a new image: `buildah commit $newcontainer newimage` (docs/buildah-commit.1.md: `buildah commit [options] container [image]`). Re-run commit after later config changes to bake them in.
8. Inspect with `buildah inspect $newcontainer` (container) or `buildah inspect --type=image <imagename>`; clean up with `buildah unmount $newcontainer` and `buildah rm $newcontainer`.
9. Full worked example from the buildah README (examples/lighttpd.sh): `ctr1=$(buildah from fedora); buildah run "$ctr1" -- dnf install -y lighttpd; buildah config --annotation "com.example.build.host=$(uname -n)" "$ctr1"; buildah config --cmd "/usr/sbin/lighttpd -D -f /etc/lighttpd/lighttpd.conf" "$ctr1"; buildah config --port 80 "$ctr1"; buildah commit "$ctr1" "$USER/lighttpd"`. Docs: https://github.com/containers/buildah/blob/main/docs/tutorials/01-intro.md