Transform.forward

Description

The blue axis of the transform in world space.

Manipulate a GameObject’s position on the Z axis (blue axis) of the transform in world space. Unlike Vector3.forward, Transform.forward moves the GameObject while also considering its rotation.

When a GameObject is rotated, the blue arrow representing the Z axis of the GameObject also changes direction. Transform.forward moves the GameObject in the blue arrow’s axis (Z).

For moving the GameObject on the Z axis while ignoring rotation, see Vector3.forward.

using UnityEngine;

public class Example : MonoBehaviour
{
    Rigidbody m_Rigidbody;
    float m_Speed;

    void Start()
    {
        //Fetch the Rigidbody component you attach from your GameObject
        m_Rigidbody = GetComponent<Rigidbody>();
        //Set the speed of the GameObject
        m_Speed = 10.0f;
    }

    void Update()
    {
        if (Input.GetKey(KeyCode.UpArrow))
        {
            //Move the Rigidbody forwards constantly at speed you define (the blue arrow axis in Scene view)
            m_Rigidbody.velocity = transform.forward * m_Speed;
        }

        if (Input.GetKey(KeyCode.DownArrow))
        {
            //Move the Rigidbody backwards constantly at the speed you define (the blue arrow axis in Scene view)
            m_Rigidbody.velocity = -transform.forward * m_Speed;
        }

        if (Input.GetKey(KeyCode.RightArrow))
        {
            //Rotate the sprite about the Y axis in the positive direction
            transform.Rotate(new Vector3(0, 1, 0) * Time.deltaTime * m_Speed, Space.World);
        }

        if (Input.GetKey(KeyCode.LeftArrow))
        {
            //Rotate the sprite about the Y axis in the negative direction
            transform.Rotate(new Vector3(0, -1, 0) * Time.deltaTime * m_Speed, Space.World);
        }
    }
}

Another example:

using UnityEngine;

// Computes the angle between the target transform and this object

public class Example : MonoBehaviour
{
    public float angleBetween = 0.0f;
    public Transform target;

    void Update()
    {
        Vector3 targetDir = target.position - transform.position;
        angleBetween = Vector3.Angle(transform.forward, targetDir);
    }
}