UNIX for Advanced & Expert Users

open today
open yesterday
while true
{
  ## Check if we need to read a new record
  if(!today_rec)
  {
    today_rec = read_next_record(today)
    today_key = get_key(today_rec)
  }

  ## Check if we need to read a new record
  if(!yesterday_rec)
  {
    yesterday_rec = read_next_record(yesterday)
    yesterday_key = get_key(yesterday)
  }

  ## If both files are done, exit the processing loop
  if (today_rec == NULL and yesterday_rec == NULL)
    break;

  if (today_key < yesterday_key)
  {
    ## today_key is missing from the yesterday file, its an insert
    report_inserted_record(today_rec)     
    today_rec = NULL
    continue
  }
  else if (today_key > yesterday_key)
  {
    ## yesterday_key is missing from today file, its a delete
    report_deleted_record(yesterday_rec)
    yesterday_rec = NULL
    continue
  }
  else if (compare_records)
    report_changed_record(today_rec, yesterday_rec)
  
  today_rec = NULL
  yeterday_rec = NULL
}