Shell Programming and Scripting

code:-
#!/bin/sh
# @(#)get_date.T        1.1 Copyright 1993, Motorola Inc.
#       (This is a joint Tandem/SPARC file)
#
#  This script is used to return a date.  The date returned
#  is adjusted for a "past" time.  The adjustment for date
#  may be made on either the year (y), month (m), or day (d)
#  fields. NOTE: date field only except lower case letters(ymd)
#
#  Note: Output format is YYMMDD order, no current provisioning
#        is made for different output requirements
#
#  Syntax: get_date <date_field> <date_adjustment>
#               date_field: Y = year; m = month; d = day
#          date_adjustment: integer value applied to date field
#
# 1st Sept 1997 olearya Updated script to accept a date in format
#                       yymmdd and to add and subtract one day
#                       from that. The new options are "sb" and "sf"
#
##################################################
mon=`date '+%m'`
day=`date '+%d'`
yr=`date '+%Y'`

#
# Go Backward in time.
#

##################################################
# Adjust year routine, parameter 1 is the value used for ajustment.
##################################################
adj_yr()
{
yr=`expr $yr - $1`

if [ $yr -lt 0 ]
then
  yr=`expr $yr + 100`
fi

if [ $yr -lt 0 ]
then
  echo "$0:Error: invalid value for year adjustment"
  exit 1
fi

if [ $yr -le 9 ]
then
   yr="0$yr"
fi
}
##################################################
# Adjust month routine, parameter 1 is the value used for ajustment.
##################################################
adj_mon()
{
mon=`expr $mon - $1`

while [ $mon -lt 1 ]
do
  adj_yr 1
  mon=`expr $mon + 12`
done

if [ $mon -le 9 ]
then
   mon="0$mon"
fi
}
##################################################
# Adjust day routine, parameter 1 is the value used for ajustment.
##################################################
adj_day()
{
day=`expr $day - $1`

while [ $day -lt 1 ]
do
  adj_mon 1
  if [ $mon -eq 12 -o $mon -eq 10 -o \
       $mon -eq 8 -o $mon -eq 7 -o $mon -eq 5 -o $mon -eq 3 -o $mon -eq 1 ]
  then
     day=`expr $day + 31`
  else
     if [ $mon -eq 2 ]
     then
        leap_yr=`expr $yr % 4`
        if [ $leap_yr -eq 0 ]
        then
          day=`expr $day + 29`
        else
          day=`expr $day + 28`
        fi
     else
        day=`expr $day + 30`;
     fi
  fi
done

if [ $day -le 9 ]
then
   day="0$day"
fi
}


#
# Go forward in time.
#
##################################################
# Adjust year routine, parameter 1 is the value used for ajustment.
##################################################
adj_yr_fwd()
{
yr=`expr $yr + $1`

if [ $yr -gt 99 ]
then
  yr=`expr $yr - 100`
fi

if [ $yr -lt 0 ]
then
  echo "$0:Error: invalid value for year adjustment"
  exit 1
fi

if [ $yr -le 9 ]
then
   yr="0$yr"
fi
}
##################################################
# Adjust month routine, parameter 1 is the value used for ajustment.
##################################################
adj_mon_fwd()
{
mon=`expr $mon + $1`

while [ $mon -gt 12 ]
do
  adj_yr_fwd 1
  mon=`expr $mon - 12`
done

if [ $mon -le 9 ]
then
   mon="0$mon"
fi
}
##################################################
# Adjust day routine, parameter 1 is the value used for adjustment.
##################################################
adj_day_fwd()
{
day=`expr $day + $1`
leap_yr=`expr $yr % 4`

case $mon in
  2|02)
    if [ $leap_yr -ne 0 ] && [ $day -gt 28 ]
    then
       adj_mon_fwd 1
       day=1
    fi;;
  1|01|3|03|5|05|7|07|8|08|10|12)
    if [ $day -gt 31 ]
    then
       adj_mon_fwd 1
       day=1
    fi;;
  4|04|6|06|9|09|11)
    if [ $day -gt 30 ]
    then
       adj_mon_fwd 1
       day=1
    fi;;
esac

if [ $day -le 9 ]
then
   day="0$day"
fi
}
##################################################
# execution body of get_date
##################################################

if [ $# -ne 2 ]
then
  echo "Error: `basename $0` <date_field> <date_adjustment>"
  echo "               date_field: Y = year; m = month; d = day"
  echo "               date_field: sb = date supplied, one day back"
  echo "               date_field: sf = date supplied, one day forward"
  echo "          date_adjustment: integer value applied to date field"
  echo "          date_adjustment: with options sb,sf is date in format yymmdd"
  echo "          eg get_date d 1        Go back one day from current date."
  echo "          eg get_date sf 970221  Go forward one day from given date."
  exit 1;
fi

case $1 in
  "y") adj_yr $2;;
  "m") adj_mon $2;;
  "d") adj_day $2;;
  "sb") yr=`echo $2 | cut -c1,2`; mon=`echo $2 | cut -c3,4`;day=`echo $2 | cut -c5,6`; adj_day 1;;
  "sf") yr=`echo $2 | cut -c1,2`; mon=`echo $2 | cut -c3,4`;day=`echo $2 | cut -c5,6`; adj_day_fwd 1;;
  *) echo "Error: `basename $0` <date_field> <date_adjustment>"
     echo "               date_field: y = year; m = month; d = day (lower case only)"
     echo "               date_field: sb = date supplied, one day back"
     echo "               date_field: sf = date supplied, one day forward"
     echo "          date_adjustment: integer value applied to date field"
     echo "          date_adjustment: with options sb,sf is date in format yymmdd"
     echo "          eg get_date d 1        Go back one day from current date."
     echo "          eg get_date sf 970221  Go forward one day from given date."
     exit 1;;
esac

echo $yr$mon$day
exit 0