Build docker image including version with bitbucket pipelines - continuous-integration

Question

I'm pretty new to Bitbucket Pipelines and I encountered a problem. I'm creating a pipeline to deploy a new version of our Spring Boot application (which runs in a Kubernetes cluster) to our test environment. The problem I encountered is the versioning of our docker build. Our versioning is set up as the following:
alpha_0.1
alpha_0.2
beta_1.0
gamma_1.0
gamma_1.1
So every minor update/bugfix increases the build number by 0.1, and a major update increases the version by 1.0 + every major update gets a new version name.
Currently I have the next setup:
image: java:8
options:
docker: true
branches:
master:
- step:
caches:
- gradle
script:
- ./gradlew test
- ./gradlew build
- docker build -t <application_name>/<version_name>_<version_number>
What is the best way to include the version_name and the version_number in the bitbucket pipeline? Until now we runned ruby script which allowed user input for version numbering, but bitbucket pipelines are not interactive.

Answer 1

Assuming that alpha_0.1 etc. are tags and that the pipeline runs if a commit is tagged, you can get the tag for the current commit like this:
TAG=$(git tag --contains $BITBUCKET_COMMIT)
You can then use your favorite language or command-line tool to create the <version_name> and <version_number> from the tag you got. It may make sense to export the tag as a shell variable to be able to use it in a script.

Answer 2

This is one of the shippable.yml files I have, feel free to adapt it to Atlassian's pipelines.yml and Gradle:
language: java
jdk:
- oraclejdk8
branches:
only:
- master
...
build:
ci:
# Generates build number
- BUILD_NUMBER=`git log --oneline | wc -l`
- echo "Build number':' ${BUILD_NUMBER}"
# Sets version
- mvn versions:set -DnewVersion=1.0.${BUILD_NUMBER}
# Builds and pushes to Docker Hub
- mvn package
- docker login -u ${DOCKERHUB_USERNAME} -p ${DOCKERHUB_PASSWD} --email ${DOCKERHUB_EMAIL} https://index.docker.io/v1/
- mvn -X docker:build -Dpush.image=true
My projects version (in pom.xml) are set to 0-SNAPSHOPT
This also uses Spotify's Maven plugin to build the Docker image instead of docker build -t ...