Using variables to dynamically check out a repository using a specific branch or tag in Azure DevOps Pipelines

In Azure DevOps pipeline, you might want to check out a repository using a specific branch or tag, in this blog post – I am going to show how you can use variables to dynamically achieve this!

Why dynamic?

My thought on creating pipelines is that I usually want it to be as dynamic as possible – so many possibilities – rather than static values, I much prefer dynamic- that I can set or change on a specific runtime when select specific values when I want to run the pipeline

The setup

I have two repositories:

https://github.com/thomast1906/dynamic-checkout-repo that has two pipelines:

https://github.com/thomast1906/dynamic-checkout-repo2 is a secondary repo – that I will be referencing in each of these pipelines

Pipeline for branch variable

For each pipeline, I will be using parameter/variable as below for branch

parameters:
  - name: branch
    displayName: branch
    type: string
    default: 'testbranch'

variables:
  - name: branch_name
    value: ${{ parameters.branch }}

Notice the below repositories ref? With $(branch_name) being used

resources:
  repositories:
  - repository: dynamic-checkout-repo2
    type: github
    ref: 'refs/heads/$(branch_name)'
    name: thomast1906/dynamic-checkout-repo2
    endpoint: 'thomast1906'

To show this working, I am running a simple stage with two checkouts, one for the current repository and the additional repository with specific branch

stages:
  - stage: stage1
    jobs:
    - job: stage1job
      steps:
        - checkout: self
        - checkout: dynamic-checkout-repo2

Reviewing Azure DevOps – we can see it working correctly and repository dynamic-checkout-repo2 using the testbranch that I defined in parameters of the pipeline

Reviewing the log output, we can see the branch testbranch has been checked out

Starting: Checkout thomast1906/dynamic-checkout-repo2@testbranch to s/dynamic-checkout-repo2
==============================================================================
Task         : Get sources
Description  : Get sources from a repository. Supports Git, TfsVC, and SVN repositories.
Version      : 1.0.0
Author       : Microsoft
Help         : [More Information](https://go.microsoft.com/fwlink/?LinkId=798199)
==============================================================================
Syncing repository: thomast1906/dynamic-checkout-repo2 (github)
git version
git version 2.37.1
git lfs version
git-lfs/3.2.0 (GitHub; linux amd64; go 1.18.2)

Pipeline for tag variable

Using same approach, lets look at tag variable

parameters:
  - name: tag
    displayName: tag
    type: string
    default: '0.0.1'

variables:
  - name: tag_name
    value: ${{ parameters.tag }}

resources:
  repositories:
  - repository: dynamic-checkout-repo2
    type: github
    ref: 'refs/tags/$(tag_name)'
    name: thomast1906/dynamic-checkout-repo2
    endpoint: 'thomast1906'

stages:
  - stage: stage1
    jobs:
    - job: stage1job
      steps:
        - checkout: self
        - checkout: dynamic-checkout-repo2

We can see the repository has a release 0.0.1 available