getAOD <- function(user = 'EarthDataUsername' # enter your user name
               ,pw = 'EarthDataPassword' # enter your password
               ,dir = 'OutputDestinationFolder'# enter a path to directory
               ,product = 'MCD19A2' # default product for MAIAC AOD
               ,date = '2018.08.28' # day of interest
               ,tile = 'h09v04' # your tile id (depends on your location)
               ,collection = "006") {

  # parse date and julian date for url building
  Date <- lubridate::ymd(date)
  julianDate <- paste0(lubridate::year(Date)
                   ,lubridate::yday(Date))

  # extracts hdf files for a given tile across all observation times
  pattern <- paste0(product, ".A", julianDate, ".", tile, ".", collection, "*.hdf")

  # base url for wget
  url <- paste0("https://e4ftl01.cr.usgs.gov/MOTA/", product, ".", collection, "/", date, "/")

  # call wget from command line
  system(paste0("wget -r -A", pattern, " -L --user=", user
            ," --password=", pw
            ," --directory-prefix=", dir
            ," --load-cookies ~/.cookies --save-cookies ~/.cookies ", url))

}

getAOD(user = 'myUserName'
    ,pw = scan("./batteries.dppss", what = "")
    ,dir = "./test")