Edit in JSFiddle

var myApp = angular.module('myApp', []);

myApp.directive('myKeypressEnter', [function () {
    return function (scope, element, attrs) {
        element.on('keypress', function (event) {
            if (event.keyCode === 13) {
                scope.$apply(function () {
                    scope.$eval(attrs.myKeypressEnter);
                });
            }
        });
    };
}]);

myApp.controller('fooCtrl', ['$scope', function ($scope) {
    $scope.enter = function (str) {
        alert(str + ' ' + $scope.input);
    };
}]);

<div ng-app="myApp" ng-controller="fooCtrl">
    <input type="text" my-keypress-enter="enter('Your input is')" ng-model="input" placeholder="press enter..." />
</div>