AIX环境下计算昨天日期的shell两例

aaa=`echo $TZ|sed 's/.*/(../)//1/'`
aaa=`expr $aaa + 24`
eval aaa=`echo $TZ|sed 's/..$/+$aaa/'`
TZ=$aaa
export TZ
yy=`date +%Y`
mm=`date +%m`
dd=`date +%d`
echo $yy$mm$dd

#!/bin/bash
# Var Declare
#!/bin/sh
# ydate: A Bourne shell script that
# prints yestarday's date
# Output Form: Month Day Year

# Set the current month day and year.
month=`date +%m`
day=`date +%d`
year=`date +%Y`

# Add 0 to month. This is a
# trick to make month an unpadded integer.
month=`expr $month + 0`

# Subtract one from the current day.
day=`expr $day - 1`

# If the day is 0 then determine the last
# day of the previous month.
if [ $day -eq 0 ]; then

# Find the preivous month.
month=`expr $month - 1`

# If the month is 0 then it is Dec 31 of
# the previous year.
if [ $month -eq 0 ]; then
month=12
day=31
year=`expr $year - 1`

# If the month is not zero we need to find
# the last day of the month.
else
case $month in
1|3|5|7|8|10|12) day=31;;
4|6|9|11) day=30;;
2)
if [ `expr $year % 4` -eq 0 ]; then
if [ `expr $year % 400` -eq 0 ]; then
day=29
fi
else
day=28
fi
;;
esac
fi
fi

echo yesterday:$year-${month}-${day}

#!/bin/bash
# Var Declare
#!/bin/sh
# ydate: A Bourne shell script that
# prints yestarday's date
# Output Form: Month Day Year

# Set the current month day and year.
month=`date +%m`
day=`date +%d`
year=`date +%Y`

# Add 0 to month. This is a
# trick to make month an unpadded integer.
month=`expr $month + 0`

# Subtract one from the current day.
day=`expr $day - 1`

# If the day is 0 then determine the last
# day of the previous month.
if [ $day -eq 0 ]; then

# Find the preivous month.
month=`expr $month - 1`

# If the month is 0 then it is Dec 31 of
# the previous year.
if [ $month -eq 0 ]; then
month=12
day=31
year=`expr $year - 1`

# If the month is not zero we need to find
# the last day of the month.
else
case $month in
1|3|5|7|8|10|12) day=31;;
4|6|9|11) day=30;;
2)
if [ `expr $year % 4` -eq 0 ]; then
if [ `expr $year % 400` -eq 0 ]; then
day=29
fi
else
day=28
fi
;;
esac
fi
fi

case $day
in 1|2|3|4|5|6|7|8|9) day='0'$day
esac
case $month
in 1|2|3|4|5|6|7|8|9) month='0'$month
esac
echo $year$month$day