Shell Programming and Scripting

#!/bin/ksh93
#date
printf "%T\n" now
printf "%(Today is %F or you can write %d.%m.%Y ...)T  \n" now

# save date to variable in standard format
timestamp=$(printf "%(%F+%H:%M:%S)T" now)
echo "timestamp:$timestamp"

# convert timestring as integer using variable
timestamp=$(printf "%(%Y-%m-%d+%H:%M:%S)T" now)
timeint=$(printf "%(%#)T" "$timestamp")
echo "timestamp:$timestamp"
echo "timeint:$timeint"
((daysec=24*60*60))
((yesterday=timeint - daysec))
((tomorrow=timeint + daysec))
# argument is # + date integer
#same = give integer using #char
printf "yesterday %(%Y-%m-%d)T  \n" "#$yesterday"
printf "tomorrow %(%Y-%m-%d)T  \n" "#$tomorrow"

sec19700101=$(printf "%(%s)T" "$d")
echo "sec since 1970-01-01 00:00 UTC: $sec19700101"
echo "= same as timeint:$timeint"

printf "day of week, monday=1: %(%u)T  \n" '#'$timeint
printf "weeknr, monday is first day of week: %(%V)T  \n" '#'$timeint

oldday=$(printf "%(%#)T"   "2008-08-15+00:00:00")
today=$(printf "%(%#)T"   "2009-08-15+00:00:00")
(( diff=(today-oldday)/(24*60*60)  ))
echo "diff:$diff"

((daysec=24*60*60))
dstr=20100228
y=${dstr:0:4}
m=${dstr:4:2}
d=${dstr:6:2}

day=$(printf "%(%#)T"   "$y-$m-$d+00:00:00")
((prev=day-daysec))
printf "%(%Y%m%d)T  \n" "#$prev"
day=$(printf "%(%#)T"   "$y-$m-$d")
((next=day+daysec))
printf "%(%Y%m%d)T  \n" "#$next"