Execute external bash script inside GitLab-ci Docker build

I would like to execute an external (on the local machine) bash script from gitlab-ci.yml which uses the docker:stable image. I would like to execute startup.sh located outside the gitlab docker image. Is this possible or are there better options?

gitlab-ci.yaml

image: docker:stable

#Build script

variables:
  CI_DEBUG_TRACE: "true"
  DOCKER_DRIVER: overlay

before_script:
  - docker --version

build:
  services:
  - docker:dind
  script:
    - docker build --no-cache -t <tag> .
    - docker login -u root -p <pass> <registry>
    - docker tag ...
    - docker push ...
    - echo "build completed"
  stage: build
  tags:
    - <tag>

deploy_staging:
  stage: deploy
  script:
    - ./sh startup.sh

bash script

#!/bin/bash

docker login -u root -p <pass>
docker pull <image>
docker-compose up -d