Ways to Define Variables

• In yaml file (``)
• In pipeline settings UI

Define variable in yaml file

variables:
  foo: xxx
  bar: yyy
  
# ... ... ...

Define variable in pipeline settings UI

Variable Types

• User-defined variables: created in yaml file or in UI settings
• System-defined (pre-defined) variables: https://docs.microsoft.com/en-us/azure/devops/pipelines/process/variables?view=azure-devops&tabs=yaml%2Cbatch#system-variables

Injection of Variables as Environment Variable

• Variables and “variables in Variable Group” will be injected as environment variables into the pipeline tasks/scripts
• Automatically inserted into the process environment
• Translation:
  • The name is upper-cased, and the “.” is replaced with the “_”
  • Example:
    • “foo.bar” will be “FOO_BAR”
    • In PowerShell Script task, use: $env:FOO_BAR

Variable Syntax

Defining variables

• Syntax 1: variables keyword is followed by a list of key-value pairs
• Syntax 2: the variables keyword takes a list of variable specifiers
  • useful when you want to use variable templates or variable groups
  • this syntax should be used at the root level of a pipeline
  • name for a regular variable, group for a variable group, and template to include a variable template

Syntax 1 (define variable)

variables:
  foo: xxx
  bar: yyy
  
# ... ... ...

Syntax 2 (define variable)

variables:
- name: myvariable # a regular variable
  value: myvalue
- group: myvariablegroup # a variable group
- template: myvariabletemplate.yml # a reference to a variable template

# ... ... ...

Usage of Variables

• $(var)
  • Called “macro syntax”
  • Macro syntax is designed to interpolate variable values into task inputs and into other variables
• $[variables.var]
  • Called “Runtime expression syntax”
  • Runtime expressions are designed to be used in the conditions of jobs, to support conditional execution of jobs, or whole stages
• $
  • Called “Template expression syntax”
  • Template variables are processed at compile time, and are replaced before runtime starts
  • Template expressions are designed for reusing parts of YAML as templates.
• Deatils: https://docs.microsoft.com/en-us/azure/devops/pipelines/process/variables?view=azure-devops&tabs=yaml%2Cbatch#runtime-expression-syntax

variables:
- group: demo-vg # has varibales: foo-one & foo-two


jobs:
- job: DemoJob
  displayName: Demo Job
  continueOnError: false
  steps:
  - task: DemoTask@1
    inputs:
	  # ... ... ...
  env:
	FOO_ONE: $(foo-one)
	FOO_TWO: $(foo-two)


# ... ... ...

Variable Scope

• Variables can be defined at different scope i.e. at root level (pipeline/yaml file), stage level, job level etc.
• Variable at lower level will override variable with same name in higher level

# Variable at yaml file / pipeline scope
variables: 
- name: fooVar 
  value: Foo
  
stages
  - stage: BuildStage
    displayName: Demo Build Stage
	jobs
	  - job: DemoJob
	    displayName: Demo Job
		variables: # Variable at job scope
		- name: barVar
		  value: Bar

Expansion of Variables

https://docs.microsoft.com/en-us/azure/devops/pipelines/process/variables?view=azure-devops&tabs=yaml%2Cbatch#expansion-of-variables

Links

• Define variables: https://docs.microsoft.com/en-us/azure/devops/pipelines/process/variables?view=azure-devops&tabs=yaml
• Predefined variables: https://docs.microsoft.com/en-us/azure/devops/pipelines/build/variables?view=azure-devops&tabs=yaml
• Classic release and artifacts variables: https://docs.microsoft.com/en-us/azure/devops/pipelines/release/variables?view=azure-devops&tabs=batch