Accessing a variable from another script C# [duplicate]

You first need to get the script component of the variable, and if they're in different game objects, you'll need to pass the Game Object as a reference in the inspector.

For example, I have scriptA.cs in GameObject A and scriptB.cs in GameObject B:

scriptA.cs

// make sure its type is public so you can access it later on
public bool X = false;

scriptB.cs

public GameObject a; // you will need this if scriptB is in another GameObject
                     // if not, you can omit this
                     // you'll realize in the inspector a field GameObject will appear
                     // assign it just by dragging the game object there
public scriptA script; // this will be the container of the script

void Start(){
    // first you need to get the script component from game object A
    // getComponent can get any components, rigidbody, collider, etc from a game object
    // giving it <scriptA> meaning you want to get a component with type scriptA
    // note that if your script is not from another game object, you don't need "a."
    // script = a.gameObject.getComponent<scriptA>(); <-- this is a bit wrong, thanks to user2320445 for spotting that
    // don't need .gameObject because a itself is already a gameObject
    script = a.getComponent<scriptA>();
}

void Update(){
    // and you can access the variable like this
    // even modifying it works
    script.X = true;
}

just for completing the first answer

there is no need for

a.gameObject.getComponent<scriptA>();

a is already a GameObject so this will do

a.getComponent<scriptA>();

and if the variable you are trying to access is in children of the GameObject you should use

a.GetComponentInChildren<scriptA>();

and if you need a variable of it or method you can access it like this

a.GetComponentInChildren<scriptA>().nameofyourvar;
a.GetComponentInChildren<scriptA>().nameofyourmethod(Methodparams);

You can use static here.

here is the example:

ScriptA.cs

Class ScriptA : MonoBehaviour{
 public static bool X = false;
}

ScriptB.cs

Class ScriptB : MonoBehaviour{
 void Update() {
   bool AccesingX = ScriptA.X;
   // or you can do this also 
   ScriptA.X = true;
 }
}

OR

ScriptA.cs

Class ScriptA : MonoBehaviour{

//you are actually creating instance of this class to access variable.
 public static ScriptA instance;

 void Awake(){

     // give reference to created object.
     instance = this;

 }

 // by this way you can access non-static members also.
 public bool X = false;


}

ScriptB.cs

Class ScriptB : MonoBehaviour{
 void Update() {
   bool AccesingX = ScriptA.instance.X;
   // or you can do this also 
   ScriptA.instance.X = true;
 }
}

for more detail, you can refer singleton class.