How to share the $scope variable of one controller with another in AngularJS?

app.controller('foo2', function ($scope) {
    $scope.$$prevSibling.bar="bar"
});

You could use an Angular Service to share variable acrosss multiple controllers.

angular.module('myApp', [])
.service('User', function () {
    return {};
})

To share the data among independent controllers, Services can be used. Create a service with the data model that needs to be shared. Inject the service in the respective controllers.

function ControllerA($scope, User) {
    $scope.user = User;
    $scope.user.firstname = "Vinoth";
}

function ControllerB($scope, User) {
    $scope.user = User;
    $scope.user.lastname = "Babu";        
}

You just can use $emit/$broadcast for translate changes of data from one controller scope to another. Or just store these variables on $rootScope.