Shell Programming and Scripting

perl -e 'print time."\n"'

truss /usr/bin/date 2>&1 | grep ^time | awk -F"= " '{print $2}'

epoch_time_start=`date +%s -d"$1"`
epoch_time_end=`date +%s -d"$2"`
total_time=`expr $epoch_time_end - $epoch_time_start`

Get date values of the date to be converted for second, minute, hour, day, month, year.

if month > 2 then
  month=month+1
else
  month=month+13
  year=year-1
fi

day=(year*365)+(year/4)-(year/100)+(year/400)+(month*306001/10000)+day
days_since_epoch=day-719591 (which is Jan 1 1970)
seconds_since_epoch=(days_since_epoch*86400)+(hour*3600)+(minute*60)+seconds