[StackOverflow/docker] Can't pass GitLab user-defined variable through Docker image with --build-arg

### ROOT CAUSE The issue arises because GitLab CI/CD variables are environment variables, while Docker build arguments (`--build-arg`) require explicit definition during the `docker build` command. The GitLab variable is not automatically passed to Docker build arguments unless explicitly included. Additionally, spaces or special characters in the variable value can break the command if not properly quoted. ### CODE FIX Modify the GitLab CI job to explicitly pass the variable as a Docker build argument. Use double quotes to handle spaces in the variable value and ensure the variable is defined in the GitLab CI job. **Example Fix:** ```yaml build_job: script: - docker build \ --build-arg MY_VAR="$MY_VAR" \ --build-arg ANOTHER_VAR="$ANOTHER_VAR" \ -t my-image . ``` **Explanation:** 1. **Explicit Build Arguments:** Replace implicit GitLab CI variables with explicit `--build-arg` flags in the `docker build` command. 2. **Quoting Variables:** Use double quotes (`"$VAR"`) to preserve spaces and special characters in the variable values. 3. **Variable Definition:** Ensure the variables (e.g., `MY_VAR`) are defined in the GitLab CI job configuration (project settings or job environment). This ensures the variables are correctly passed to Docker during the build.