advtime

#!/bin/sh
#########################################################################
# advtime.sh								#
#									#
#  This script is used to advance forward or backward in date/time.	#
#									#
#  Log:									#
#  K. Brill/HPC		 9/01	Created from advtime in C shell		#
#  K. Brill/HPC		11/01	Trap 2-digit year invalid date		#
#########################################################################

if [ $# -eq 0 ]; then
   cat << EOF

   This script goes forward or backward in time beginning at the
   starting time.

   Command line inputs are:

 	YYYYMMDDHH	=	starting year month day hour
 	DH		=	time increment in hours (- => backward)
 	NDH		=	number of increments
 
	If NDH is negative, the first time is not output; otherwise,
 	there will be NDH + 1 output times. 

	Any fourth command line input triggers output times in GEMPAK
        format, YYYYMMDD/HH; otherwise, the output format is the same
        as the input format, YYYYMMDDHH.

EOF
    exit
fi

ymdh=$1
cnt=`echo $ymdh | wc -c`
if [ $cnt -lt 10 ]; then
    echo $ymdh is not valid for YYYYMMDDHH
    exit 1
fi
dh=`expr $2 + 0`
ndh=`expr $3 + 0`

if [ $ndh -lt 0 ]; then
    ndh=`expr -1 \* $ndh`
    first=2
else
    first=1
fi

monday="31 28 31 30 31 30 31 31 30 31 30 31"
yy=`echo $ymdh | cut -c1-4`
mm=`echo $ymdh | cut -c5-6`
dd=`echo $ymdh | cut -c7-8`
hh=`echo $ymdh | cut -c9-10`

times=${yy}${mm}${dd}/${hh}
ymdhs=${yy}${mm}${dd}${hh}

ddd=$dd
mmm=$mm

dd=`expr $dd + 0`
mm=`expr $mm + 0`
yy=`expr $yy + 0`

hr=`expr $hh + 0`
icnt=0

while [ $icnt -lt $ndh ]; do
    icnt=`expr $icnt + 1`
    hr=`expr $hr + $dh`

    while [ $hr -lt 0 ]; do
	hr=`expr $hr + 24`
	dd=`expr $dd - 1`
	if [ $dd -eq 0 ]; then
	    mm=`expr $mm - 1`
	    if [ $mm -eq 0 ]; then
		yy=`expr $yy - 1`
		mm=12
	    fi
	    mmm=$mm
    	    if [ $mm -lt 10 ]; then
		mmm=0$mm
	    fi
	    dd=`echo $monday | cut -d" " -f$mm`
	    leap=0
	    if [ `expr $yy % 400` -eq 0 ]; then
		leap=1
	    elif [ `expr $yy % 4` -eq 0 -a `expr $yy % 100` -ne 0 ]; then
		leap=1
	    fi
	    if [ $leap -eq 1 -a $mm -eq 2 ]; then
		 dd=`expr $dd + 1`
	    fi
	fi
	ddd=$dd
    	if [ $dd -lt 10 ]; then
	    ddd=0$dd
	fi
    done
    while [ $hr -ge 24 ]; do
	hr=`expr $hr - 24`
	dd=`expr $dd + 1`
	dtst=`echo $monday | cut -d" " -f$mm`
	mm=$mm
	yy=$yy
	leap=0
	if [ `expr $yy % 400` -eq 0 ]; then
	    leap=1
	elif [ `expr $yy % 4` -eq 0 -a `expr $yy % 100` -ne 0 ]; then
	    leap=1
	fi
	if [ $leap -eq 1 -a $mm -eq 2 ]; then
	     dtst=`expr $dtst + 1`
	fi
	if [ $dd -gt $dtst ]; then
	    mm=`expr $mm + 1`
	    if [ $mm -eq 13 ]; then
		yy=`expr $yy + 1`
		mm=1
	    fi
	    mmm=$mm
    	    if [ $mm -lt 10 ]; then
		mmm=0$mm
	    fi
	    dd=1
	fi
	ddd=$dd
    	if [ $dd -lt 10 ]; then
	    ddd=0$dd
	fi
    done
    hhh=$hr
    if [ $hr -lt 10 ]; then
	hhh=0$hr
    fi
    yyy=$yy
    if [ $yy -lt 10 ]; then
	 yyy=0$yy
    fi
    times="$times ${yyy}${mmm}${ddd}/${hhh}"
    ymdhs="$ymdhs ${yyy}${mmm}${ddd}${hhh}"
done

if [ $# -eq 4 ]; then
    i=0
    for t in $times; do
	i=`expr $i + 1`
    	if [ $i -ge $first ]; then
	    echo $t
	fi
    done
else
    i=0
    for t in $ymdhs; do
	i=`expr $i + 1`
    	if [ $i -ge $first ]; then
	    echo $t
	fi
    done
fi