I have a backup directory with a few hundred thousand files, several thousand from each day. I want to tar up the files into 1 or more files for each day. I can use the find command with -mtime to get files that are 'x' number of days old, but how do I get today's date minus 'x' into a variable of the form 'YYYYMMDD' so that I can use it as part of the tar file name?

var=`date +%Y%m%d`

That gives me today's date. When I do a find command with the -mtime option, I want today's date - 'x' where x is the number of days I'm going back to do the archiving.

Carl:

In an earler thread in this forum named:

count days since jan 1 1970

discusses this particular problem. In this thread, I say what a pain date arithmetic is with non-GNU tools. While Perl is probably your best choice, you can do it in the shell using Scaliger's Julian Date. I'm including it here for your perusal:

Regards,

Nails

#!/bin/sh

# Scaliger's Julian date (JD) is a continuous count of days from 1 January
# 4713 BC. The following algorithm is good from years 1801 to 2099
# See URL:http://aa.usno.navy.mil/faq/docs/JD_Formula.html for
# more information. arguments are
# day, month, year
get_JD () {
# calculation below is all on one line.
# Also the bc calcuator is being called with a unix "here" document, so you need 2 less than arrows between bc and MSG. This forum wipes them out:
bc MSG
scale=0
$1-32075+1461*($3+4800+($2-14)/12)/4+367*($2-2-($2-14)/12*12)/12-3*(($3+4900+($2-14)/12)/100)/4
MSG
}

jd1970=`get_JD 1 1 1970`
jd1971=`get_JD 1 1 1971`
diff=`expr $jd1971 - $jd1970`
echo $diff # still 365 days

Try

shift_date $(date +%Y%m%d) -1

I tried the shift suggestion but couldn't get the 'date - 1' part to ever work.

Nails: The formula you provided works great. Do you have a compact formula for getting back the year, month, and day components from the Julian date?

Not 'date - 1', 'shift_date -1'. My shift_date script takes two parameters: the first is a date in YYYYMMDD format, the second is an integer which can be negative. It works to my knowledge on HPUX, Solaris and FreeBSD.

Carl:

Yup, there is. In the interest of full-disclosure, this is from an article from Sys Admin, "Date Arithmetic with the Shell" by Kyle Douglass and Ed Schaefer.

They got the algorithm's from USNO:

# This function computes the gregorian date from the julian date - $1. Returns
a
# date string of the form: MONTH DAY YEAR
# See URL: http://aa.usno.navy.mil/faq/docs/JD_Formula.html for more information
get_greg_from_JD ()
{
typeset -i L
typeset -i N
typeset -i I
typeset -i J
typeset -i DAY
typeset -i MON
typeset -i YR

L=$(($1+68569)) # $1 is the julian date
N=$((4*L/146097))
L=$((L-(146097*N+3)/4))
I=$((4000*(L+1)/1461001))
L=$((L-1461*I/4+31))
J=$((80*L/2447))
DAY=$((L-2447*J/80))
L=$((J/11))
MON=$((J+2-12*L))
YR=$((100*(N-49)+I+L))

echo $MON $DAY $YR
}

TY=$(date '+%Y') # Year for today - MUST be YYYY
TM=$(date '+%m') # Month for today
TD=$(date '+%d') # Day for today
# printf "%s %s %s\n" $TM $TD $TY
JD=$(get_JD TD TM TY) # today's JD
# yesterday's date
yesterdays_date_str=$(get_greg_from_JD $((JD-1)) )
# parse yesterdays date string
set - $(echo $yesterdays_date_str)
echo $1 # month
echo $2 # day
echo $3 # year

Regards,

Nails

oh oh oh

its very hard to work with dates under unix, because there is no spezify tool for it!

my solution is, that "we" have a oracle server installed on the unix machine, so i can calculate the date with sql:

backup_datum=`sqlplus -s EOF
user/password
set head off
set feed off
select to_char(sysdate - $1 ,'YYYYMMDD') from dual;
EOF`

this is another way to do it!

regards

Jonny

> this is another way to do it!

Well clearly two possible solutions are described above.

Perhaps you could explain a bit more why neither of them seems to be what you need.

@ William

that is my old script:

#!/bin/ksh
#########################################################"
# Script name : calculate_date.sh"
# Path : /home/oracle/dba/bin"
# Author : Jonny Schulz"
# Rheinland Versicherungen"
# Create : 27.06.2003"
# Change :"
# Of :"

# Description"
# This Script calculate Date."
#########################################################"

#####################
### VARIABLES ###
#####################

date=`date +'%Y.%m.%d'`
yyyy=`date +'%Y'`
yy=`date +'%y'`
month=`date +'%m'`
day=`date +'%d'`
sign=$1
count=$2
format=$3

#####################
### FUNCTIONS ###
#####################

do_help()
{
echo ""
echo "#########################################################"
echo "# Script name : calculate_date.sh"
echo "# Path : /home/oracle/dba/bin"
echo "# Author : Jonny Schulz"
echo "# Rheinland Versicherungen"
echo "# Create : 27.06.2003"
echo "# Change :"
echo "# Of :"
ec---"
echo "# Description"
echo "# This Script calculate Date."
echo "#########################################################"
echo ""
echo " Please enter the following parameters:"
echo " calculate_date.sh [+/-] [0123456789] [1/2/3/4/5/6/7/8]"
echo ""
echo " [+/-] = Art to calculate"
echo " [0123456789] = Count days"
echo " [1/2/3/4/5/6/7/8] = Which format"
echo ""
echo " Possible formats:"
echo " ------------------"
echo " YYYY.MM.DD (1)"
echo " YYYYMMDD (2)"
echo " YY.MM.DD (3)"
echo " YYMMDD (4)"
echo " DD.MM.YYYY (5)"
echo " DDMMYYYY (6)"
echo " DD.MM.YY (7)"
echo " DDMMYYYY (8)"
echo ""
echo ""
}

minus()
{
while [[ $count != 0 ]]
do
count=$(($count-1))
case $month in
01 ) day=$(($day-1))
if [[ $day = 0 ]]
then
day=31
month=12
year=$(($year-1))
fi
;;

02 ) day=$(($day-1))
if [[ $day = 0 ]]
then
day=31
month=01
fi
;;

03 )
leap_year=`bc EOF
scale=8
$year/4
EOF`

leap_year=`echo $leap_year | cut -d'.' -f2`

day=$(($day-1))
if [[ $day = 0 ]]
then
if [[ $leap_year = "00000000" ]]
then
day=29
month=02
else
day=28
month=02
fi
fi
;;

04 ) day=$(($day-1))
if [[ $day = 0 ]]
then
day=31
month=03
fi
;;

05 ) day=$(($day-1))
if [[ $day = 0 ]]
then
day=30
month=04
fi
;;

06 ) day=$(($day-1))
if [[ $day = 0 ]]
then
day=31
month=05
fi
;;

07 ) day=$(($day-1))
if [[ $day = 0 ]]
then
day=30
month=06
fi
;;

08 ) day=$(($day-1))
if [[ $day = 0 ]]
then
day=31
month=07
fi
;;

09 ) day=$(($day-1))
if [[ $day = 0 ]]
then
day=31
month=08
fi
;;

10 ) day=$(($day-1))
if [[ $day = 0 ]]
then
day=30
month=09
fi
;;

11 ) day=$(($day-1))
if [[ $day = 0 ]]
then
day=31
month=10
fi
;;

12 ) day=$(($day-1))
if [[ $day = 0 ]]
then
day=30
month=11
fi
;;
esac
done
}

plus()
{
while [[ $count != 0 ]]
do
count=$(($count-1))
case $month in
01 ) day=$(($day+1))
if [[ $day = 32 ]]
then
day=01
month=02
fi
;;

02 )
leap_year=`bc EOF
scale=8
$year/4
EOF`

leap_year=`echo $leap_year | cut -d'.' -f2`

day=$(($day+1))
if [[ $leap_year = "00000000" ]]
then
if [[ $day = 30 ]]
then
day=01
month=03
fi
else
if [[ $day = 29 ]]
then
day=01
month=03
fi
fi
;;

03 ) day=$(($day+1))
if [[ $day = 32 ]]
then
day=01
month=04
fi
;;

04 ) day=$(($day+1))
if [[ $day = 31 ]]
then
day=01
month=05
fi
;;

05 ) day=$(($day+1))
if [[ $day = 32 ]]
then
day=01
month=06
fi
;;

06 ) day=$(($day+1))
if [[ $day = 31 ]]
then
day=01
month=07
fi
;;

07 ) day=$(($day+1))
if [[ $day = 32 ]]
then
day=01
month=08
fi
;;

08 ) day=$(($day+1))
if [[ $day = 32 ]]
then
day=01
month=09
fi
;;

09 ) day=$(($day+1))
if [[ $day = 31 ]]
then
day=01
month=10
fi
;;

10 ) day=$(($day+1))
if [[ $day = 32 ]]
then
day=01
month=11
fi
;;

11 ) day=$(($day+1))
if [[ $day = 31 ]]
then
day=01
month=12
fi
;;

12 ) day=$(($day+1))
if [[ $day = 32 ]]
then
day=01
month=01
year=$(($year+1))
fi
;;
esac
done
}

################
### MAIN ###
################

case $format in
1 | 2 | 5 | 6 ) year=$yyyy ;;
3 | 4 | 7 | 8 ) year=$yy ;;
* ) do_help ;;
esac

if [[ $sign = "+" ]]
then
plus
else
if [[ $sign = "-" ]]
then
minus
else
do_help
fi
fi

case $day in
1 ) day="01" ;;
2 ) day="02" ;;
3 ) day="03" ;;
4 ) day="04" ;;
5 ) day="05" ;;
6 ) day="06" ;;
7 ) day="07" ;;
8 ) day="08" ;;
9 ) day="09" ;;
esac

case $year in
1 ) year="01" ;;
2 ) year="02" ;;
3 ) year="03" ;;
4 ) year="04" ;;
5 ) year="05" ;;
6 ) year="06" ;;
7 ) year="07" ;;
8 ) year="08" ;;
9 ) year="09" ;;
esac

case $format in
1 | 3 ) date_calculate=${year}.${month}.${day}
;;
2 | 4 ) date_calculate=echo ${year}${month}${day}
;;
5 | 7 ) date_calculate=echo ${day}.${month}.${year}
;;
6 | 8 ) date_calculate=echo ${day}${month}${year}
;;
esac

echo $date_calculate

exit 0

unfortunately the runtime is bad!
for this reason i create a new script and use the sql statement. i only had surch for a better script, but no script use a better runtime...