In Azure DevOps Pipelines, variables play a crucial role in defining and controlling the behavior of your CI/CD (Continuous Integration/Continuous Deployment) pipelines. These variables can be used to store values that are utilized across different stages and jobs within your pipeline. Variables are often used for things like connection strings, authentication tokens, environment-specific settings, and more.

There are two main types of variables in Azure DevOps Pipelines:

1. Pipeline Variables: These are defined at the pipeline level and are accessible across all stages and jobs within the pipeline. Pipeline variables are defined in the YAML file that defines your pipeline, usually at the top level. They can be set using the variables section.

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   trigger: branches: include: - main variables: myVariable: "Hello, World!" jobs: - job: Build steps: - script: echo $(myVariable)

2. Job and Step Level Variables: These are defined within specific jobs or steps and are only accessible within that particular context. They can be set using the jobs and steps sections in your YAML file.

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   jobs: - job: Build steps: - script: echo $(Build.SourcesDirectory) # Predefined system variable - script: echo $(myJobVariable) # Job-level variable defined below displayName: "Echo Job Variable" - job: Deploy variables: myJobVariable: "This is a job-level variable" steps: - script: echo $(myJobVariable) displayName: "Echo Job Variable in Deploy Job"

Apart from these, you also have access to predefined system variables and environment variables.

Predefined System Variables: Azure DevOps provides a set of predefined variables that hold information about your pipeline, repository, and more. Examples include Build.ArtifactStagingDirectory, Build.SourceBranch, Agent.JobStatus, etc.

Environment Variables: Environment variables can be used to pass information to your scripts and tools during the execution of pipeline steps. These variables can be set explicitly in your YAML or derived from pipeline or system values.

To set pipeline variables dynamically based on conditions, you can use expression syntax within your YAML:

Remember that variables in YAML pipelines are case-insensitive and support different syntaxes for variable interpolation, such as $(variableName) or ${{ variables.variableName }}.

Using variables in Azure DevOps Pipelines allows you to maintain flexibility and reusability while ensuring that sensitive data is not hard-coded in your pipeline configuration. They provide a way to customize and parameterize your pipeline’s behavior based on different environments and scenarios.