OSStatus err = [task launch];
if (err != errAuthorizationSuccess) {
    if (err == errAuthorizationCanceled) {
        NSLog(@"User cancelled");
        return;
    }  else {
        NSLog(@"Something went wrong: %d", (int)err);
        // For error codes, see http://www.opensource.apple.com/source/libsecurity_authorization/libsecurity_authorization-36329/lib/Authorization.h
    }
}

[task waitUntilExit];

NSFileHandle *readHandle = [task outputFileHandle];
NSData *outputData = [readHandle readDataToEndOfFile];
NSString *outputString = [[NSString alloc] initWithData:outputData encoding:NSUTF8StringEncoding];
NSLog(@"outputString=%@",outputString);