ecearth3/sources/tm5mp/bin/date_add

#!/bin/csh -ef

set prog = `basename $0`

if ( ${#argv} < 2 ) then
  cat << EOF
  usage : $prog ccyymmdd increment
EOF
  exit( 1 )
endif

# --- const ------------------------------------

set ndaymon = ( '31' '28' '31' '30' '31' '30' '31' '31' '30' '31' '30' '31' )

# --- arguments -----------------------------

set datein = $1
set ddays = $2

# --- begin -------------------------------

# extract parts without leading zeros:
set year  = `echo $datein | /usr/bin/cut -c 1-4`
set month = `echo $datein | /usr/bin/cut -c 5-6`
set day   = `echo $datein | /usr/bin/cut -c 7-8`

# on IBM, '09' means octal '9' which is an error ...
if ( $month =~ 0? ) set month = `echo $month | /usr/bin/cut -c 2`
if ( $day   =~ 0? ) set day   = `echo $day   | /usr/bin/cut -c 2`

# Initialize results without leading zeros:
@ day2   = ${day}
@ month2 = $month
@ year2  = $year

if ( $ddays > 0 ) then

  @ day2 = $day2 + $ddays

  while ( 1 )
  
    @ ndays = $ndaymon[$month2]
    if ( $month2 == 2 ) then
      if ( $year2 %   4 == 0 ) set ndays = 29
      if ( $year2 % 100 == 0 ) set ndays = 28
      if ( $year2 % 400 == 0 ) set ndays = 29
    endif

    if ( $day2 <= $ndays ) break
    
    @ day2 = $day2 -  $ndays
    @ month2 = $month2 + 1
    if ( $month2 > 12 ) then
      @ year2  = $year2 + 1
      @ month2 = 1
    endif

  end

else

  @ day2 = $day2 + $ddays
  while ( 1 )

    if ( $day2 >= 1 ) break
    
    @ month2 = $month2 - 1
    if ( $month2 == 0 ) then
      @ year2 = $year2 - 1
      @ month2 = 12
    endif

    @ ndays = $ndaymon[$month2]
    if ( $month2 == 2 ) then
      if ( $year2 %   4 == 0 ) set ndays = 29
      if ( $year2 % 100 == 0 ) set ndays = 28
      if ( $year2 % 400 == 0 ) set ndays = 29
    endif

    @ day2 = $day2 +  $ndays

  end
  
endif

# Make resulting day, month, year 2 digits:
if ( $day2   < 10 ) set day2   = "0${day2}"
if ( $month2 < 10 ) set month2 = "0${month2}"

# display the result:
echo "${year2}${month2}${day2}"