add option to keep v prefix in tag

README.md

@@ -127,6 +127,7 @@ These keys mirror the [Swarmia Deployment API](https://help.swarmia.com/settings
 | `docker-image`              | Docker Image                                                                                                                   |                                                      |
 | `docker-custom-tag`         | Docker Custom Tag to be set on the image                                                                                       |                                                      |
 | `docker-tag-timestamp`      | Insert a UTC timestamp into `dev`/`main`/`master` branch tags (`dev-<timestamp>-<short-sha>`) to make them sortable for Flux image automation | `false`                              |
+| `docker-tag-keep-v-prefix`  | Keep the leading `v` on release (`v*`) tags (`v1.2.3` → `v1.2.3`). Default strips it (`v1.2.3` → `1.2.3`) | `false`                                           |
 | `docker-username`           | Username for the Docker Registry                                                                                               |                                                      |
 | `docker-password`           | Password for the Docker Registry                                                                                               |                                                      |
 | `docker-file`               | Dockerfile                                                                                                                     | `./Dockerfile`                                       |
@@ -163,7 +164,7 @@ The generated image tag depends on the Git ref:
 | `dev` branch | `dev-<short-sha>` | `dev-<utc-timestamp>-<short-sha>` | `dev` |
 | `main` branch | `main-<short-sha>` | `main-<utc-timestamp>-<short-sha>` | `main` |
 | `master` branch | `master-<short-sha>` | `master-<utc-timestamp>-<short-sha>` | `master` |
-| `v*` tag (prod) | the version, e.g. `2025.50.14` (CalVer) | _(unchanged)_ | `latest` |
+| `v*` tag (prod) | the version with the `v` stripped, e.g. `v2025.50.14` → `2025.50.14` (or kept with `docker-tag-keep-v-prefix: 'true'`) | _(unchanged)_ | `latest` |
 | other branch | `<short-sha>` (not pushed) | _(unchanged)_ | — |
 
 By default branch tags keep the legacy `<prefix>-<short-sha>` shape. Set

action.yml

@@ -21,6 +21,10 @@ inputs:
     description: 'Insert a UTC timestamp into dev/main/master branch tags (e.g. dev-20260602143055-<short-sha>) to make them sortable for Flux image automation. Opt-in; defaults to the legacy <prefix>-<short-sha> format.'
     required: false
     default: 'false'
+  docker-tag-keep-v-prefix:
+    description: 'Keep the leading "v" on release (v*) tags (v1.2.3 -> v1.2.3). Opt-in; defaults to stripping it (v1.2.3 -> 1.2.3).'
+    required: false
+    default: 'false'
   docker-username:
     description: 'Username for the Docker Registry'
     required: false
@@ -117,6 +121,7 @@ runs:
       env:
         INPUT_DOCKER_CUSTOM_TAG: ${{ inputs.docker-custom-tag }}
         INPUT_DOCKER_TAG_TIMESTAMP: ${{ inputs.docker-tag-timestamp }}
+        INPUT_DOCKER_TAG_KEEP_V_PREFIX: ${{ inputs.docker-tag-keep-v-prefix }}
         INPUT_DOCKER_DISABLE_RETAGGING: ${{ inputs.docker-disable-retagging }}
         INPUT_DOCKER_REGISTRY: ${{ inputs.docker-registry }}
         INPUT_DOCKER_IMAGE: ${{ inputs.docker-image }}

scripts/generate-tags.sh

@@ -2,7 +2,8 @@
 # Generates Docker image tags based on the current Git ref.
 #
 # Required env vars: GITHUB_REF, GITHUB_SHA, INPUT_DOCKER_REGISTRY, INPUT_DOCKER_IMAGE
-# Optional env vars: INPUT_DOCKER_CUSTOM_TAG, INPUT_DOCKER_DISABLE_RETAGGING
+# Optional env vars: INPUT_DOCKER_CUSTOM_TAG, INPUT_DOCKER_DISABLE_RETAGGING,
+#                    INPUT_DOCKER_TAG_TIMESTAMP, INPUT_DOCKER_TAG_KEEP_V_PREFIX
 #
 # Outputs (via GITHUB_OUTPUT): build, latest, push, tag, tag_list
 
@@ -65,7 +66,13 @@ elif [[ $GITHUB_REF == refs/heads/dev ]]; then
   LATEST="dev"
   PUSH="true"
 elif [[ $GITHUB_REF == refs/tags/v* ]]; then
-  TAG="${GITHUB_REF:11}"
+  # By default the leading "v" is stripped (v1.2.3 -> 1.2.3). Set
+  # INPUT_DOCKER_TAG_KEEP_V_PREFIX=true to keep it (v1.2.3 -> v1.2.3).
+  if [[ "${INPUT_DOCKER_TAG_KEEP_V_PREFIX:-false}" == "true" ]]; then
+    TAG="${GITHUB_REF#refs/tags/}"
+  else
+    TAG="${GITHUB_REF:11}"
+  fi
   LATEST="latest"
   PUSH="true"
   BUILD="${INPUT_DOCKER_DISABLE_RETAGGING:-false}"

tests/generate-tags.bats

@@ -14,6 +14,8 @@ setup() {
   # Timestamp suffix is opt-in; default off so the legacy <prefix>-<sha> format
   # is the baseline. Tests that exercise the suffix set the flag explicitly.
   unset INPUT_DOCKER_TAG_TIMESTAMP
+  # Keeping the "v" prefix on release tags is opt-in; default off.
+  unset INPUT_DOCKER_TAG_KEEP_V_PREFIX
   # Pin the timestamp so the opt-in branch tags are deterministic in tests.
   export BUILD_TIMESTAMP="20260602143055"
 }
@@ -143,6 +145,31 @@ teardown() {
   assert_output_value "push" "true"
 }
 
+@test "version tag strips the v prefix by default" {
+  export GITHUB_REF="refs/tags/v1.2.3"
+  run "$SCRIPT"
+  assert_success
+  assert_output_value "tag" "1.2.3"
+}
+
+@test "version tag keeps the v prefix when flag is enabled" {
+  export INPUT_DOCKER_TAG_KEEP_V_PREFIX="true"
+  export GITHUB_REF="refs/tags/v1.2.3"
+  run "$SCRIPT"
+  assert_success
+  assert_output_value "tag" "v1.2.3"
+  assert_output_value "latest" "latest"
+  assert_output_value "push" "true"
+}
+
+@test "keep-v-prefix flag does not affect non-v tags" {
+  export INPUT_DOCKER_TAG_KEEP_V_PREFIX="true"
+  export GITHUB_REF="refs/tags/release-1"
+  run "$SCRIPT"
+  assert_success
+  assert_output_value "tag" "release-1"
+}
+
 @test "version tag uses docker-disable-retagging for build flag" {
   export GITHUB_REF="refs/tags/v1.2.3"
   export INPUT_DOCKER_DISABLE_RETAGGING="true"