How to quit itself in Objective-C application?

I have a URLHandler that launches some application, the main code is as follows.

@implementation URLHandlerCommand

- (id)performDefaultImplementation {
    NSString *urlString = [self directParameter];

    NSLog(@"url :=: %@", urlString);

    NSTask *task;
    task = [[NSTask alloc] init];
    [task setLaunchPath: @"/usr/bin/open"];

    NSArray *arguments;
    arguments = [NSArray arrayWithObjects: @"-a", @"Path Finder.app", urlString, nil];
    [task setArguments: arguments];

    NSPipe *pipe;
    pipe = [NSPipe pipe];
    [task setStandardOutput: pipe];

    NSFileHandle *file;
    file = [pipe fileHandleForReading];

    [task launch];

    return nil;
}

As the goal of this routine is to launch another application, I'd like to make this URLHandler quit after launching an App. How can I do that?