Elegant Implementation of Conditional Logic in GitHub Actions

Introduction

In GitHub Actions workflows, developers often need to execute different steps based on conditions. However, the native workflow syntax does not support an else statement directly. This article delves into multiple techniques to achieve conditional branching, providing detailed examples and best practices.

Core Method: Using Reversed Conditions

As highlighted in the best answer, GitHub Actions lacks an explicit else statement. The recommended approach is to create separate steps with reversed conditions using the if keyword. For instance, to check if a BUILD_VERSION contains 'SNAPSHOT', one step can have the condition contains(['SNAPSHOT'], env.BUILD_VERSION) and another with the negated condition !contains(['SNAPSHOT'], env.BUILD_VERSION). It is advisable to use the negation operator ! for clarity, such as ${{ !contains(['SNAPSHOT'], env.BUILD_VERSION) }}. This method avoids code duplication but requires careful design to prevent logical errors.

Supplementary Methods

Other answers provide additional techniques that can serve as complements to the core method, suitable for more complex scenarios:

• Multiple Conditional Steps: As shown in the second answer, define unique conditions for each step, allowing selective execution based on different criteria without explicit else statements. For example, use conditions at the job level to skip entire jobs or set independent steps for different message conditions.
• Third-Party Actions: The third answer mentions using actions like haya14busa/action-cond for setting dynamic values, particularly useful when conditions affect step parameters without duplicating entire steps. This can reduce workflow complexity and improve maintainability.
• Shell Script Commands: The fourth answer suggests using shell if-else statements within run commands, such as in Ubuntu environments. This method offers flexibility but may make workflows harder to manage and debug due to logic scattered in shell code.
• Expression-Based Logic: The fifth answer demonstrates using expressions like ${{ x && 'ifTrue' || 'ifFalse' }} to compute values directly, suitable for simple conditional assignments, such as setting environment variables. However, it might not be ideal for complex or multi-branch conditions.

Conclusion and Recommendations

While GitHub Actions does not have built-in else functionality, developers can effectively emulate conditional logic by using reversed if conditions as the foundational approach, combined with other techniques like third-party actions or shell scripts. In practice, prioritize reversed conditions to maintain workflow simplicity; for advanced needs, evaluate using multiple steps or actions. Understanding these options enables the design of robust and scalable automation processes.