PlayerMovement.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class PlayerMovement : MonoBehaviour
{
    [SerializeField] private float moveSpeed;
    [SerializeField] private float walkSpeed;
    [SerializeField] private float runSpeed;

    private Vector3 moveDirection;
    private Vector3 velocity;

    [SerializeField] private bool isGrounded;
    [SerializeField] private float groundCheckDistance;
    [SerializeField] private LayerMask groundMask;
    [SerializeField] private float gravity;
    [SerializeField] private float jumpHeight;

    private CharacterController controller;
    private Animator anim;

    private void Start() {

        controller = GetComponent<CharacterController>();
        anim = GetComponentInChildren<Animator>();

    }

    private void Update()
    {
        Move();
        if (Input.GetKeyDown(KeyCode.Mouse0))
        {
            
            StartCoroutine(Attack());
        }
    }

    private void Move() {

        isGrounded = Physics.CheckSphere(transform.position, groundCheckDistance, groundMask);

        if (isGrounded && velocity.y < 0) {
            velocity.y = -2f;
        }

        float moveZ = Input.GetAxis("Vertical");
        moveDirection = new Vector3(0, 0, moveZ);
        moveDirection = transform.TransformDirection(moveDirection);



        if (isGrounded) {

            if (moveDirection != Vector3.zero && !Input.GetKey(KeyCode.LeftShift))
        {
            Walk();
        }
            else if (moveDirection != Vector3.zero && Input.GetKey(KeyCode.LeftShift)) {
            
            Run();
               
            }   else if (moveDirection == Vector3.zero) {

            Idle();
        }
            moveDirection *= moveSpeed;
            controller.Move(moveDirection * Time.deltaTime);


            if (Input.GetKeyDown(KeyCode.Space)) {
                Jump();
            }

        }
        
        velocity.y += gravity * Time.deltaTime;
        controller.Move(velocity * Time.deltaTime);

    }

    private void Idle() {
        anim.SetFloat("Speed", 0, 0.1f, Time.deltaTime);
    }

    private void Walk() {
         moveSpeed = walkSpeed;
        anim.SetFloat("Speed", 0.5f, 0.1f, Time.deltaTime);
    }
    private void Run() {
         moveSpeed = runSpeed;
        anim.SetFloat("Speed", 1, 0.1f, Time.deltaTime);
    }

    private void Jump() {
        velocity.y = Mathf.Sqrt(jumpHeight * -2 * gravity);
    }

    private IEnumerator Attack() {
        //Temporary fix.
        anim.SetLayerWeight(anim.GetLayerIndex("Attack Layer"), 1);
        anim.SetTrigger("Attack");

        yield return new WaitForSeconds(1);
        anim.SetLayerWeight(anim.GetLayerIndex("Attack Layer"), 0);
    }
}