In Azure DevOps, variables are a fundamental concept used to store and manage data that can be used in various parts of your pipelines and releases. Azure DevOps provides different types of variables that serve different purposes. Here are some key aspects of Azure DevOps variables:

1. Pipeline Variables:

   • Pipeline variables are defined within a specific pipeline (build or release).
   • They can be used to store values that are specific to a single pipeline run.
   • Pipeline variables are scoped to a specific stage or job within the pipeline.

2. Environment Variables:

   • Environment variables are system-level variables available to all jobs and tasks within a pipeline.
   • They can be used to store values that are common across different stages or jobs in a pipeline.
   • Environment variables can be defined at the pipeline or stage level.

3. Secret Variables:

   • Secret variables are used to store sensitive information such as API keys, passwords, or other confidential data.
   • They are encrypted and not displayed in logs or exposed in the pipeline configuration.
   • Secret variables can be defined at the pipeline or stage level.

4. Variable Groups:

   • Variable groups are a way to store and manage sets of variables that can be reused across multiple pipelines.
   • They are useful for centralizing and standardizing variable values.
   • Variable groups can also be marked as secret to store sensitive data.

5. Variable Precedence:

   • Variables in Azure DevOps follow a specific order of precedence. Pipeline variables have the highest precedence, followed by stage-level variables, environment variables, and finally, system variables.
   • In case of variable name conflicts, variables with higher precedence take precedence over lower-precedence ones.

6. Variable Syntax:

   • Variables in Azure DevOps are referenced using a specific syntax, such as $(variableName).
   • The value of a variable can be referenced and used in tasks, scripts, or expressions within your pipeline.

7. Variable Use Cases:

   • Variables can be used for a wide range of purposes, including storing connection strings, build numbers, release version numbers, deployment paths, and more.
   • They are often used to parameterize pipeline configurations, making them more flexible and reusable.

8. Variable Set and Change:

   • Variables can be set and changed during a pipeline run using tasks or scripts.
   • This allows you to dynamically update variable values based on conditions or external inputs.

9. Logging and Debugging:

   • The values of variables can be logged in pipeline execution logs for debugging purposes.
   • However, secret variables are masked in logs to protect sensitive data.

10. Variable Group Permissions:

    • Access to variable groups can be controlled using Azure DevOps permissions.
    • Only users or groups with the appropriate permissions can modify or view the contents of a variable group.

11. Multi-Stage Pipelines:

    • Variables can be used across stages in multi-stage pipelines to pass data and configuration information between different parts of the pipeline.

12. Expression Evaluation:

    • Azure DevOps allows you to use expressions to evaluate and manipulate variable values within pipeline tasks and conditions.

Azure DevOps variables provide a flexible and powerful way to manage and parameterize your pipelines and releases. They enable you to store and use data effectively, customize your pipeline behavior, and ensure the security of sensitive information. Understanding the different types of variables and their scope is essential for effectively configuring and controlling your CI/CD processes.