diff --git a/.gitea/workflows/build-and-push.yml b/.gitea/workflows/build-and-push.yml
index 303ef2f..4999be6 100644
--- a/.gitea/workflows/build-and-push.yml
+++ b/.gitea/workflows/build-and-push.yml
@@ -24,10 +24,10 @@ jobs:
               uses: actions/checkout@v4
             - name: Set image tags
               id: vars
-              shell: bash
+              shell: sh
               run: |
-                  SHORT_SHA="${GITHUB_SHA::7}"
-                  BRANCH="${GITHUB_REF_NAME//\//-}"
+                  SHORT_SHA=$(printf '%s' "$GITHUB_SHA" | cut -c1-7)
+                  BRANCH=$(printf '%s' "$GITHUB_REF_NAME" | tr '/' '-')
 
                   echo "short_sha=${SHORT_SHA}" >> "$GITHUB_OUTPUT"
                   echo "branch=${BRANCH}" >> "$GITHUB_OUTPUT"