Provide outputs as env vars

Signed-off-by: CrazyMax <crazy-max@users.noreply.github.com>

Author: crazy-max

.github/workflows/ci.yml

@@ -37,6 +37,9 @@ jobs:
             type=ref,event=tag
             type=ref,event=pr
             type=sha
+      -
+        name: Print envs
+        run: env|sort
 
   tag-schedule:
     runs-on: ubuntu-latest
@@ -224,6 +227,14 @@ jobs:
           echo "version=${{ fromJSON(steps.meta.outputs.json).labels['org.opencontainers.image.version'] }}"
           echo "revision=${{ fromJSON(steps.meta.outputs.json).labels['org.opencontainers.image.revision'] }}"
           echo "created=${{ fromJSON(steps.meta.outputs.json).labels['org.opencontainers.image.created'] }}"
+      -
+        name: JSON build arg
+        uses: docker/build-push-action@v3
+        with:
+          context: ./test
+          file: ./test/json.Dockerfile
+          build-args: |
+            BUILDINFO=${{ steps.meta.outputs.json }}
 
   docker-push:
     runs-on: ubuntu-latest
@@ -350,3 +361,31 @@ jobs:
         with:
           script: |
             console.log(`${{ steps.meta.outputs.tags }}`);
+
+  output-env:
+    runs-on: ubuntu-latest
+    steps:
+      -
+        name: Checkout
+        uses: actions/checkout@v3
+      -
+        name: Docker meta
+        id: meta
+        uses: ./
+        with:
+          images: |
+            ${{ env.DOCKER_IMAGE }}
+            ghcr.io/name/app
+          labels: |
+            maintainer=CrazyMax
+      -
+        name: Build
+        uses: docker/build-push-action@v3
+        with:
+          context: ./test
+          file: ./test/output.Dockerfile
+          build-args: |
+            DOCKER_METADATA_OUTPUT_VERSION
+            DOCKER_METADATA_OUTPUT_TAGS
+            DOCKER_METADATA_OUTPUT_LABELS
+            DOCKER_METADATA_OUTPUT_JSON

README.md

@@ -297,6 +297,23 @@ Following outputs are available
 | `json`        | String  | JSON output of tags and labels                                                             |
 | `bake-file`   | File    | [Bake file definition](https://docs.docker.com/build/customize/bake/file-definition/) path |
 
+Alternatively, each output is also exported as an environment variable:
+
+* `DOCKER_METADATA_OUTPUT_VERSION`
+* `DOCKER_METADATA_OUTPUT_TAGS`
+* `DOCKER_METADATA_OUTPUT_LABELS`
+* `DOCKER_METADATA_OUTPUT_JSON`
+* `DOCKER_METADATA_OUTPUT_BAKE_FILE`
+
+So it can be used with our [Docker Build Push action](https://github.com/docker/build-push-action/):
+
+```yaml
+- uses: docker/build-push-action@v3
+  with:
+    build-args: |
+      DOCKER_METADATA_OUTPUT_JSON
+```
+
 ### environment variables
 
 | Name                          | Type | Description                                                                                                |

src/main.ts

@@ -41,7 +41,7 @@ async function run() {
       core.info(version.main || '');
       core.endGroup();
     }
-    core.setOutput('version', version.main || '');
+    setOutput('version', version.main || '');
 
     // Docker tags
     const tags: Array<string> = meta.getTags();
@@ -54,7 +54,7 @@ async function run() {
       }
       core.endGroup();
     }
-    core.setOutput('tags', tags.join(inputs.sepTags));
+    setOutput('tags', tags.join(inputs.sepTags));
 
     // Docker labels
     const labels: Array<string> = meta.getLabels();
@@ -63,24 +63,29 @@ async function run() {
       core.info(label);
     }
     core.endGroup();
-    core.setOutput('labels', labels.join(inputs.sepLabels));
+    setOutput('labels', labels.join(inputs.sepLabels));
 
     // JSON
     const jsonOutput = meta.getJSON();
     core.startGroup(`JSON output`);
     core.info(JSON.stringify(jsonOutput, null, 2));
     core.endGroup();
-    core.setOutput('json', jsonOutput);
+    setOutput('json', JSON.stringify(jsonOutput));
 
     // Bake file definition
     const bakeFile: string = meta.getBakeFile();
     core.startGroup(`Bake file definition`);
     core.info(fs.readFileSync(bakeFile, 'utf8'));
     core.endGroup();
-    core.setOutput('bake-file', bakeFile);
+    setOutput('bake-file', bakeFile);
   } catch (error) {
     core.setFailed(error.message);
   }
 }
 
+function setOutput(name: string, value: string) {
+  core.setOutput(name, value);
+  core.exportVariable(`DOCKER_METADATA_OUTPUT_${name.replace(/\W/g, '_').toUpperCase()}`, value);
+}
+
 run();

test/json.Dockerfile

@@ -0,0 +1,6 @@
+# syntax=docker/dockerfile:1
+FROM alpine
+RUN apk add --no-cache coreutils jq
+ARG BUILDINFO
+RUN printenv BUILDINFO
+RUN echo $BUILDINFO | jq

test/output.Dockerfile

@@ -0,0 +1,12 @@
+# syntax=docker/dockerfile:1
+FROM alpine
+RUN apk add --no-cache coreutils jq
+ARG DOCKER_METADATA_OUTPUT_VERSION
+ARG DOCKER_METADATA_OUTPUT_TAGS
+ARG DOCKER_METADATA_OUTPUT_LABELS
+ARG DOCKER_METADATA_OUTPUT_JSON
+RUN printenv DOCKER_METADATA_OUTPUT_VERSION
+RUN printenv DOCKER_METADATA_OUTPUT_TAGS
+RUN printenv DOCKER_METADATA_OUTPUT_LABELS
+RUN printenv DOCKER_METADATA_OUTPUT_JSON
+RUN echo $DOCKER_METADATA_OUTPUT_JSON | jq