Getting date one month before today using unix. 2

[RajShekar]

How to get the date 30 days before today using unix scripting? The month changes and year changes shold be considered.

 

[vgersh99]

my favorit is julian<->gregorian conversion

#-----------------------------------------------------------------------------
# Date manipulation routines - convering to Julian and back
#
# Julian Day Number from calendar date
date2julian() #  day month year
{
  typeset year=$1;  typeset month=$2;  typeset day=$3
  tmpmonth=$((12 * year + month - 3))
  tmpyear=$((tmpmonth / 12))
  print $(( (734 * tmpmonth + 15) / 24 -  2 * tmpyear +     tmpyear/4 - tmpyear/100 + tmpyear/400 + day + 1721119 ))
}

# Calendar date from Julian Day Number
julian2date() # julianday
{
  #set -x
  typeset tmpday=$(($1 - 1721119))
  typeset centuries=$(( (4 * tmpday - 1) / 146097))
  tmpday=$((tmpday + centuries - centuries/4))
  typeset year=$(( (4 * tmpday - 1) / 1461))
  tmpday=$((tmpday - (1461 * year) / 4))
  typeset month=$(( (10 * tmpday - 5) / 306))
  day=$((tmpday - (306 * month + 5) / 10))
  month=$((month + 2))
  year=$((year + month/12))
  month=$((month % 12 + 1))
  printf "%s %02d %02d" $year $month $day
}

here's how to get the previous day:

datePrevious() # $1 - year:month:day
{
    #set -x
    typeset dateI=$(echo "${1}" | sed -e "s/:/ /g");
    echo "$(julian2date $(( $(date2julian ${dateI}) - 1 )) )" | sed -e "s/ /:/g";
}

today="$(date +%Y:%M%d)"
echo "today->[${today}] yesterday->[$(datePrevious ${today})]

vlad
+----------------------------+
| #include<disclaimer.h> |
+----------------------------+

 

[PHV]

Take a look at my FAQ: faq80-4800

Hope This Help, PH.
Want to get great answers to your Tek-Tips questions? Have a look at FAQ219-2884 or FAQ222-2244

 

[Ogzilal]

Hi,

Try this shell script using perl ctime and time functions

# SECONDS_IN_30DAYS contains the number of seconds in 30 days
#
SECONDS_IN_30DAYS=0
(( SECONDS_IN_30DAYS=30 * 24 * 60 * 60 ))
# use perl functions time and ctime
# time function gives today's date in seconds sine Jan 01 1970
# ctime ( seconds) converts epoch date to locale date
perl -e " use POSIX; print ctime (time() - $SECONDS_IN_30DAYS) "

Ali

 

[Ygor]

Another way...

#!/usr/bin/ksh
Days=30
Date=$(perl -e '
  $d = time() - (86400 * $ARGV[0]);
  @f = localtime($d);
  printf "%04d%02d%02d\n", $f[5]+1900, $f[4]+1, $f[3];
  ' $Days)
echo The date $Days days ago was $Date

The date 30 days ago was 20040428

 

[johngiggs]

Good post Ygor!!

 

[dchoulette]

Another way (without perl) :

date -r$(( printf -- "-30*24*60*60+"; date +%s ) | bc)

--------------------

Denis