我想显示当天1天前的日期

Question

For every start my application it should take sysdate- 2 date. i created shell script for that. But during month ends im facing the problem. its not updating correctly.

My script

a1=`date +%d`
a1=`expr $a1 - 2`
b1=`date +%m-%Y`
rm LastTopupDate.txt
echo $a1-$b1 >> Date.txt

help me out from this problem.?

Answer 1

Assuming GNU date , you can use

a1=$(date +%s)
b1=$(date +%m-%Y --date @$((a1-2*86400)))

Syntax for other implementations may be different, but the same idea applies: a1 is the date represented as a UNIX timestamp (number of seconds since a fixed epoch), and b1 is the date that occurs 2 days (86,400 seconds in a day) earlier.

GNU date also provides a nicer shortcut:

b1=$(date +%m-%Y --date '2 days ago')

Answer 2

Answering to the title question which is about yesterday's date, here is something that should work on systems which do not provide GNU date:

h=$(date +%H)
today=$(date +%d)

for i in -12 -6 +0 +6 +12; do
        gmth=$(TZ=UTC$i date +%H)
        gmttoday=$(TZ=UTC$i date +%d)
        if [ $gmttoday == $today ] && [ $gmth -gt 4 ]; then
                TZ=UTC$((i+24)) date +%d-%m-%Y
                break
        fi
done