docs: document JSON_BASH_GREP envar in README #28

	name: Build & publish end-user images
	on:
	push:
	branches:
	- main
	tags:
	- v**

	env:
	REGISTRY: ghcr.io
	TAG_PREFIX: ghcr.io/${{ github.repository }}

	jobs:
	container_images:
	name: Build & publish end-user images
	runs-on: ubuntu-latest
	permissions:
	packages: write

	steps:
	- name: Checkout
	uses: actions/checkout@c85c95e3d7251135ab7dc9ce3241c5835cc595a9

	- name: Set up Docker Buildx
	uses: docker/setup-buildx-action@4c0219f9ac95b02789c1075625400b2acbff50b1

	- name: Log in to the container registry
	uses: docker/login-action@465a07811f14bebb1938fbed4728c6a1ff8901fc
	with:
	registry: ${{ env.REGISTRY }}
	username: ${{ github.actor }}
	password: ${{ secrets.GITHUB_TOKEN }}

	- name: Determine version
	id: version
	run: \|
	if [[ ${GITHUB_REF:?} =~ ^refs/tags/v([0-9].*)$ ]]; then
	tag_version=${BASH_REMATCH[1]:?}
	else
	# use the default in docker-bake.hcl
	tag_version=''
	fi
	echo "tag_version=${tag_version?}" \| tee -a "${GITHUB_OUTPUT:?}"

	push=false
	if [[ ${GITHUB_REF:?} =~ ^refs/tags/v[0-9]\|^refs/heads/main$ ]]; then
	push=true
	fi
	echo "push=${push:?}" \| tee -a "${GITHUB_OUTPUT:?}"

	- name: Build & publish
	uses: docker/bake-action@f32f8b8d70bc284af19f8148dd14ad1d2fbc6c28
	env:
	JSON_BASH_VERSION: ${{ steps.version.outputs.tag_version }}
	with:
	targets: pkg,jb
	files: docker-bake.hcl
	provenance: true
	sbom: true
	push: ${{ steps.version.outputs.push }}
	set: \|
	*.cache-from=type=gha
	*.cache-to=type=gha,mode=max

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