HomeUnity Game DevelopmentUnderstanding Unity Script functions and their execution

Understanding Unity Script functions and their execution


Unity, the renowned game development platform, has been the foundation of countless successful games across various platforms. One of the key pillars of Unity’s power lies in its scripting system, which allows developers to bring their game ideas to life. In this comprehensive guide, we will delve into the intricacies of Unity scripting, answering fundamental questions, and shedding light on the core concepts.

Why Unity Uses C#?

Unity primarily employs C# as its scripting language, and for good reason. C# is a versatile, object-oriented language that strikes a balance between ease of use and performance. It offers features like garbage collection, which simplifies memory management, making it an ideal choice for game development. Additionally, C# has a robust ecosystem, abundant resources, and a thriving community, making it easier for developers to find solutions to common problems.

Unity Debugger

What Language is Unity Written In?

While Unity’s scripting is predominantly done in C#, Unity itself is written in C++ for performance reasons. C++ allows Unity to access low-level systems and hardware, ensuring that the engine can achieve optimal performance on different platforms. This separation of scripting in C# and the engine core in C++ contributes to Unity’s versatility and efficiency.

Understanding the Different Components of Unity Script

Using Statements Using statements at the top of a Unity script are essential for importing external libraries and namespaces into your script. They allow you to access predefined classes, functions, and variables, saving you from reinventing the wheel. These statements are like road signs that tell your script where to find the tools it needs.

What is a Class? In Unity scripting, a class is the blueprint for objects that share common properties and behaviors. Classes are the building blocks of your game logic. You define what a class contains, such as variables and functions, and then create instances of that class, known as objects. These objects can interact with each other, creating the dynamic behavior of your game.

What is a MonoBehaviour?

A MonoBehaviour is a special type of class in Unity that allows you to attach scripts to game objects. These scripts define how a game object behaves and responds to events. MonoBehaviour scripts contain functions like Start(), Update(), and OnCollisionEnter(), which Unity’s engine calls automatically at specific points in the game’s life cycle. These functions enable you to control the behavior of your game objects easily.

Why Do We Write MonoBehaviour Inside the Script?

Writing MonoBehaviour scripts inside your Unity project is essential because they define the behavior of your game objects. Without MonoBehaviour scripts, your game objects would be lifeless and static. By attaching scripts, you breathe life into your game, allowing objects to move, interact, and respond to player input.

Do We Always Need to Write MonoBehaviour for Writing Code in Unity?

While MonoBehaviour is a fundamental component of Unity scripting, not every script needs to derive from it. Unity supports other script types as well, such as Editor scripts for customizing the Unity Editor and ScriptableObjects for creating data assets. The choice of script type depends on your specific needs and the role a script plays in your project.

Understanding the Different Functions in a Unity Script

Unity scripts consist of various functions that define the behavior of game objects. These functions are automatically called by the Unity engine at specific points during the game’s life cycle. Understanding the purpose of these functions is essential for effective game development:

  1. Awake()
    • Awake() is called when a script instance is initialized, even before Start().
    • It’s typically used for setting up references and configurations that need to be initialized before the game starts.
  2. Start()
    • Start() is called once, at the beginning of a game object’s lifetime, after Awake().
    • It’s commonly used for initial setup, like initializing variables or setting up listeners.
  3. Update()
    • Update() is called once per frame.
    • It’s often used for real-time actions such as player input processing, character movement, and other frame-dependent behaviors.
  4. FixedUpdate()
    • FixedUpdate() is called at a fixed time step, making it ideal for physics-related calculations.
    • It’s used for physics updates, rigid body interactions, and ensuring consistent behavior across different frame rates.
  5. LateUpdate()
    • LateUpdate() is called once per frame after Update().
    • It’s commonly used for camera-related scripts, ensuring that camera movements occur after all object updates to avoid jittery camera behavior.
  6. OnEnable() and OnDisable()
    • These functions are called when a script component is enabled or disabled.
    • They are used for managing resource allocation and cleanup when objects are activated or deactivated.
  7. OnCollisionEnter() and OnCollisionExit()
    • These functions are called when a collision occurs between two colliders.
    • They are used to handle collision events and perform actions when objects interact physically.
  8. OnTriggerEnter() and OnTriggerExit()
    • These functions are called when a collider enters or exits a trigger zone.
    • They are useful for defining trigger-based interactions and detecting when objects enter specific areas without physical collisions.
  9. OnDestroy()
    • OnDestroy() is called when a game object is about to be destroyed.
    • It’s used for cleaning up resources, releasing memory, and performing final actions before an object is removed from the scene.

Unity’s Script Execution Order

Understanding the execution order of these functions is crucial for controlling the flow of your game and ensuring that scripts behave as expected:

  1. Initialization Phase
    • Awake(): Initialization of script instances.
    • Start(): Initialization after Awake() but before the first frame update.
  2. Update Phase
    • Update(): Called once per frame, ideal for real-time updates.
    • LateUpdate(): Called once per frame after Update(), suitable for camera-related actions.
  3. FixedUpdate Phase
    • FixedUpdate(): Called at fixed intervals (physics time step), used for physics calculations.
  4. Collision and Trigger Events
    • OnCollisionEnter(), OnCollisionExit(): Called when colliders collide.
    • OnTriggerEnter(), OnTriggerExit(): Called when objects enter or exit trigger zones.
  5. Finalization and Destruction
    • OnDisable(): Called when a script component is disabled.
    • OnDestroy(): Called when an object is about to be destroyed.

It’s important to note that Unity automatically manages the execution order based on these phases, ensuring that physics calculations occur before update functions and that events like collisions are processed at the appropriate time.

When you have multiple scripts on a single game object, Unity allows you to specify the script execution order in the Unity Editor. This feature enables you to control the sequence in which scripts run, ensuring that dependencies and interactions between scripts are well-defined.


Mastering Unity scripting is a journey that opens the door to creating immersive and engaging games. In this guide, we’ve explored the core concepts of Unity scripting, from the choice of C# as the primary language to the importance of understanding script execution order. Armed with this knowledge, you’re well-equipped to navigate the world of Unity game development with confidence.

Interview Question: Imagine you’re developing a 2D platformer game in Unity where the player character has multiple abilities, such as jumping, shooting, and interacting with objects. You have implemented these abilities using separate scripts attached to the player game object. However, you’ve encountered issues with the timing and order of execution of these scripts, leading to unintended behavior. How would you ensure that the scripts execute in the desired order to maintain the game’s functionality and performance in this specific platformer game scenario? Please explain the key considerations and tools available in Unity to achieve this.


This guide should serve as a valuable resource as you embark on your Unity game programming journey, providing you with a solid foundation for creating stunning and interactive games. Happy coding!



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