http://www.unix.com/tips-tutorials/31944-simple-date-time-calulation-bash.html
#!/bin/bash
date2stamp () {
date --utc --date "$1" +%s
}
stamp2date (){
date --utc --date "1970-01-01 $1 sec" "+%Y-%m-%d %T"
}
dateDiff (){
case $1 in
-s) sec=1; shift;;
-m) sec=60; shift;;
-h) sec=3600; shift;;
-d) sec=86400; shift;;
*) sec=86400;;
esac
dte1=$(date2stamp $1)
dte2=$(date2stamp $2)
diffSec=$((dte2-dte1))
if ((diffSec < 0)); then abs=-1; else abs=1; fi
echo $((diffSec/sec*abs))
}
## USAGE # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
#
## convert a date into a UNIX timestamp
# stamp=$(date2stamp "2006-10-01 15:00")
# echo $stamp
#
## from timestamp to date
# stamp2date $stamp
#
## calculate the number of days between 2 dates
# # -s in sec. | -m in min. | -h in hours | -d in days (default)
# dateDiff -s "2006-10-01" "2006-10-32"
# dateDiff -m "2006-10-01" "2006-10-32"
# dateDiff -h "2006-10-01" "2006-10-32"
# dateDiff -d "2006-10-01" "2006-10-32"
# dateDiff "2006-10-01" "2006-10-32"
#
## number of seconds between two times
# dateDiff -s "17:55" "23:15:07"
# dateDiff -m "17:55" "23:15:07"
# dateDiff -h "17:55" "23:15:07"
#
## number of minutes from now until the end of the year
# dateDiff -m "now" "2006-12-31 24:00:00 CEST"
#
## Other standard goodies from GNU date not too well documented in the man pages
# # assign a value to the variable dte for the examples below
# dte="2006-10-01 06:55:55"
# echo $dte
#
# # add 2 days, one hour and 5 sec to any date
# date --date "$dte 2 days 1 hour 5 sec"
#
# # substract from any date
# date --date "$dte 3 days 5 hours 10 sec ago"
# date --date "$dte -3 days -5 hours -10 sec"
#
# # or any mix of +/-. What will be the date in 3 months less 5 days
# date --date "now +3 months -5 days"
#
# # time conversions into ISO-8601 format (RFC-3339 internet recommended format)
# date --date "sun oct 1 5:45:02PM" +%FT%T%z
# date --iso-8601=seconds --date "sun oct 1 5:45:02PM"
# date --iso-8601=minutes
#
# # time conversions into RFC-822 format
# date --rfc-822 --date "sun oct 1 5:45:02PM"
EXPIRE_DAY=`date -d "$(chage -l digimoon | grep 'Password expires' | awk -F: '{print $2}')" +'%Y-%m-%d'`
TODAY=`date +'%Y-%m-%d'`
▼ /etc/login.defs 파일의 "PASS_MAX_DAYS" 옵션에 정의한 날짜에 의해 정해진 시스템 계정의 password expire 날짜가 다가오기까지 얼마나 남았는지 알려주기 위한 용도의 스크립트 예
(계정별 expire 날짜는 "chage -l <계정명>"으로 확인 가능)
# expire 날짜가 100일 이하 남은 경우 계정 경고 if [ "$(dateDiff -d "$TODAY" "$EXPIRE_DAY")" -le 100 ] ; then echo "digimoon 계정이 expire 날짜로부터 $(dateDiff -d "$TODAY" "$EXPIRE_DAY")일 남았습니다!!!" fi
