github-slug-action/docs/how-to/use-slugs-in-urls.md

Use slug variables in URLs

Use SLUG_URL variables (not SLUG) when building URLs, because SLUG_URL also replaces dots and underscores with hyphens, making values safe for subdomains and URL paths.

As a subdomain

steps:
  - uses: actions/checkout@v6
  - uses: rlespinasse/github-slug-action@v5
  - run: |
      ./deploy-application.sh --url "https://${{ env.GITHUB_REF_SLUG_URL }}.staging.app.example.com"

For a branch feat/new_feature, this produces https://feat-new-feature.staging.app.example.com.

As a URL path segment

steps:
  - uses: actions/checkout@v6
  - uses: rlespinasse/github-slug-action@v5
  - run: |
      ./deploy-application.sh --url "https://staging.app.example.com/${{ env.GITHUB_REF_SLUG_URL }}"

Why SLUG_URL instead of SLUG?

The SLUG transformation preserves . and _ characters. In a subdomain like v1.0.0.staging.example.com, the dots from the version tag would create invalid DNS resolution. SLUG_URL replaces them: v1-0-0.staging.example.com.

See Slug transformation rules for the full comparison.

See also

• Full example workflow
• Variable reference for all available SLUG_URL variables