In Azure DevOps, variables are a key component used to store data that varies between builds or releases, allowing for more dynamic and flexible pipeline configurations. They can be used to manage environment settings, pass data, and control the behavior of the pipeline. Here’s a detailed overview of Azure DevOps variables:

Types of Variables

1. Predefined Variables: These are system variables provided by Azure DevOps, such as Build.BuildId or Release.ReleaseId. They give information about the current context of the pipeline run.

2. Custom Variables: Defined by the user at various levels (pipeline, stage, job) to suit specific needs. They can be used to store values like file paths, connection strings, or any other data that should not be hard-coded into the pipeline scripts.

3. Variable Groups: A way to group variables that are used across multiple pipelines. Variable groups are stored and managed in the Azure DevOps Library.

Scope of Variables

• Pipeline Variables: Defined at the pipeline level and accessible across all stages and jobs in that pipeline.
• Stage Variables: Available only within a specific stage.
• Job Variables: Accessible only within the job where they are defined.

Setting and Using Variables

• Setting Variables: Can be set in the pipeline YAML file, through the Azure DevOps portal UI, or via scripts during pipeline execution.
• Using Variables: Accessed using syntax like $(variableName) in Azure DevOps tasks and scripts.

Variable Syntax

• Inline Syntax: $(variableName) is used in most Azure DevOps tasks.
• Script Syntax: In shell scripts, variables are accessed using standard environment variable syntax like $VARIABLE_NAME in bash or %VARIABLE_NAME% in Windows batch scripts.

Runtime Parameters

• Parameters: These are special kinds of variables that are set at the time of pipeline execution (runtime). They are defined in YAML and allow for manual input or selection of values when the pipeline is run.

Secret Variables

• Secrets: Variables can be marked as ‘secret’, hiding their values in logs and UI. These are used for passwords, tokens, and other sensitive data. They require special syntax to use in scripts.

Best Practices

• Avoid Hardcoding: Use variables instead of hardcoded values to make pipelines more flexible and secure.
• Securing Sensitive Data: Always use secret variables for storing sensitive information.
• Use Descriptive Names: Name your variables descriptively so their purpose is clear.
• Leverage Variable Groups: For common variables across multiple pipelines, use variable groups to centralize management.
• Environment-Specific Variables: Use different variables or variable groups for different deployment environments (e.g., development, testing, production).

Azure DevOps variables enhance the capability to create reusable, maintainable, and dynamic pipelines. They are essential for managing different environments, customizing deployments, and securing sensitive data within the Azure DevOps CI/CD process.