A Docker tag and push script for use with Travis CI. Best results with git tags (vX.X.X).

.travis.yml

language: java
jdk:
  - oraclejdk8

branches:
  only:
    - master

services:
  - docker

cache:
  directories:
    - $HOME/.m2

env:
  - DOCKER_REPO_SLUG=<your_username>/<your_repository_name>

install:
  - mvn -DskipTests install

script:
  - mvn test

after_success:
  - docker build -t $DOCKER_REPO_SLUG:latest .

deploy:
  - provider: script
    script: bash docker_push.sh
    on:
      branch: master
  - provider: script
    script: bash docker_push.sh
    on:
      tags: true

notifications:
  email:
    recipients:
      - <your_email_address>
    on_success: never
    on_failure: always

docker_push.sh

#!/bin/bash

# Preamble: This script unfolds its full power if the git tags have the following format: vX.X.X

TAGS=()

# Splits a tag number e.g. v3.1.0 into an array of ( 3 1 0 ). The given tag must start with a lowercase "v" otherwise
# the validation fails. The array will be stored in the TAGS variable.
function split() {
    local tag=$1

    if [[ ${tag} =~ ^v([0-9]+)\.([0-9]+)\.([0-9]+)$ ]]; then
        tag=$(echo ${tag} | cut -d "v" -f 2) # Removes "v" from the tag. Eg v3.1.0 to 3.1.0
        IFS='.'                              # Overrides the internal file separator
        TAGS=(${tag})                        # Turns the tag into an array
        IFS=$OIFS                            # Restores the original separator
    else
        echo "'$tag' doesn't seem to be an acceptable tag"
        exit 1
    fi

    return 0
}

# Takes any string and tags the :latest Docker image. The image will be pushed to the Docker registry afterwards.
function tag_and_push() {
    local tag=$1

    # Omit the :latest tag
    [[ ${tag} != "latest" ]] && docker tag $DOCKER_REPO_SLUG:latest $DOCKER_REPO_SLUG:${tag}
    docker push $DOCKER_REPO_SLUG:${tag}

    return 0
}

echo "$DOCKER_PASSWORD" | docker login -u "$DOCKER_USERNAME" --password-stdin || (echo "Unable to login"; exit 1)

# Distinguish between the push and cron event of the Travis CI. A push event will always leeds to a new :edge Docker
# image, while cron leeds to a new :nightly image.
# More about Travis events and environment variables on https://docs.travis-ci.com/user/environment-variables/
case $TRAVIS_EVENT_TYPE in
    "push")
        tag_and_push "edge"
        ;;
    "cron")
        # Only tag and push with nightly if the branch matches master
        [[ $TRAVIS_BRANCH = "master" ]] && tag_and_push "nightly"
        ;;
    *)
        echo "Unknown Travis event type"
        exit 1
        ;;
esac

# Matching branch name and git tag implies a new release. The Docker image will be tagged with :latest and convenient
# version numbers. E.g. v0.0.1=>0.0.1  v0.1.0=>0.1,0.1.0  v0.1.2=>0.1,0.1.2  v1.0.0=>1,1.0,1.0.0  v1.0.3=>1,1.0,1.0.3
# v1.2.0=>1,1.2,1.2.0  v1.2.3=>1,1.2,1.2.3
if [[ $TRAVIS_TAG = $TRAVIS_BRANCH ]]; then
    split $TRAVIS_TAG

    MAJOR=${TAGS[0]}
    MINOR=${MAJOR}.${TAGS[1]}
    PATCH=${MINOR}.${TAGS[2]}

    tag_and_push "latest" # The git tag must be valid otherwise the script does not push the :latest.
    [[ ${TAGS[0]} -gt 0 ]] && tag_and_push ${MAJOR}
    [[ ${TAGS[0]} -gt 0 || ${TAGS[1]} -gt 0 ]] && tag_and_push ${MINOR}
    [[ ${TAGS[0]} -gt 0 || ${TAGS[1]} -gt 0 && ${TAGS[2]} -gt 0 ]] && tag_and_push ${PATCH}
fi

exit 0