example use of awk to format a date

time_converter.awk

function convert_time(t) {
  split(t,a,"/");
  if (a[3] > 50) {
    a[3] = sprintf("19%02d", a[3]);
  } else {
    a[3] = sprintf("20%02d", a[3]);
  }
  month = a[1];
  day = a[2];
  year = a[3];
  x = sprintf("%d %d %d 12 00 00", year, month, day);
  y = mktime(x);
  return strftime("%m/%d/%Y", y);
}

{
  print "11/30/00", "->", convert_time("11/30/00");
  print "11/30/99", "->", convert_time("11/30/99");
  print "11/30/89", "->", convert_time("11/30/89");
  print "11/30/01", "->", convert_time("11/30/01");
}