Edit in JSFiddle

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

myApp.filter('capitalize', function() {
    return function(input, scope) {
        return input.substring(0,1).toUpperCase()+input.substring(1);
    }
});

function MyCtrl($scope) {
    $scope.aString = "bonjour";
}

<div ng-controller="MyCtrl">
     {{aString | capitalize}} !
</div>