In Angular, how to get a form in $scope in controller?

I recommend using the controller itself instead of the $scope provider for this. This was one of the first issues I came across when working with angularjs

In your controller:

function MyController($scope) {
  var vm = this;
  vm.registrationForm.confirmPassword.$setValidity("PasswordsMatch", $scope.validation.doPasswordsMatch);
}

In your form:

<form name="vm.registrationForm" ng-submit="registerUser()">
   ...
</form>

The only gotcha is that you need to specify the controllerAs property in your route or ngInclude:

ng-include="templates/my-template.html" ng-controller="MyController as vm"

or

when('/my-route', {
  templateUrl: 'templates/my-template.html',
  controller: 'MyController as vm'
 })

You need to add a name attribute to form element.

<form name="registrationForm" ng-submit="registerUser()">
   ...
</form>

this form must rely on a controller indeed. please take a look at the example:

angular.module("fooApp",[]);

angular.module("fooApp")
  .controller("formctl",function(){
    this.user={};
    this.dosave=function(){
      if(this.user.pwd == this.user.confpwd)
        alert(this.user.username+" logged");
      else
        alert("pwd does not match");
    };
  });

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.5.8/angular.min.js"></script>
<div ng-app="fooApp">
  <h1>sample</h1>
  <div ng-controller="formctl as ctl">
    <form ng-submit="ctl.dosave()">
      <label>username</label><br/>
      <input ng-model="ctl.user.username" required/><br/>
      <label>password</label><br/>
      <input ng-model="ctl.user.pwd" type="password" required/><br/>
      <label>confirm password</label><br/>
      <input ng-model="ctl.user.confpwd" type="password"/><br/>
      <input type="submit"/>
    </form>
  </div>
</div>

You'll want to pass the form into the submit function to pass the entire form into the controller. Use the form name.

<form name="registrationForm" ng-submit="registerUser(registrationForm)">
...
</form>

The other option would be to pass the inputs directly in as params

<form name="myForm" novalidate >
  some input: <input type="text" name="sometext" ng-model="myInput">
  <input type="submit" ng-click="doAction(myInput)">
</form>

Quick Plunk https://plnkr.co/edit/s0Al2LTHkvUPoLYNzTpm?p=info

If you're just after the value of the inputs, it's easier to test if you have explicit parameters that you expect on the method instead of dumping in the entire form.