Hi,
Im a newbie.All your suggestions needed.
Im developing a script that should that find dat files based on the file name(file name is created has date info) after comparing it with the current timestamp.Let me put it in a clear way.
For instance,
Say I have files say like

AA_XX_20121208    /*date part in name of the file*/
AA_XX_20121207
AA_XX_20121206
AA_XX_20121205
AA_XX_20121204
AA_XX_20121203
AA_XX_20130108
AA_XX_20130107
AA_XX_20130106
AA_XX_20130105
AA_XX_20130104
AA_XX_20130103
AA_XX_20130208
AA_XX_20130207
AA_XX_20130206
AA_XX_20130205
AA_XX_20130204
AA_XX_20130203

It seems a little twisted, but it works:

YEAR=`date +%Y`
MONTH=`date +%m`
MONTH1=$(( MONTH - 1 ))
YEAR1=$YEAR
if [[ $MONTH1 -eq 0 ]]
then
MONTH1=12
YEAR1=$(( YEAR - 1 ))
fi
MONTH2=$(( MONTH1 - 1 ))
YEAR2=$YEAR1
if [[ $MONTH2 -eq 0 ]]
then
MONTH2=12
YEAR2=$(( YEAR1 - 1 ))
fi
PATTERN1=`printf "AA_XX_%s%02d" $YEAR1 $MONTH1`
PATTERN2=`printf "AA_XX_%s%02d" $YEAR2 $MONTH2`
find . -name $PATTERN1\*
find . -name $PATTERN2\*

Thanks a lot franzpizzo !!

Another sh-based alternative:

read m y <<EOF
$(date +'%m %Y')
EOF

read m1 y1 m2 y2 <<EOF
$(((m-1+11)%12+1)) $([ $m -eq 1 ] && y=$((y-1)); echo $y) \
$(((m-1+10)%12+1)) $([ $m -lt 3 ] && y=$((y-1)); echo $y)
EOF

# m1/y1 is the month/year of one month ago
# m2/y2 is the month/year of two months ago.