Shell Programming and Scripting

I have following strings in a file
DUPTASMTRMMBAL,20070416200704160117232101172321,,,,,,,@@@Y
DUPTASMTRMMCON,20070416200704160127189901271899,,,,,,,@@@Y
DUPTASMTRMMHG,,20070416200704160112051001120510,,,,,,,@@@Y

What i need to do is replace the date 20070416 with anoth date which is stored in variable enddate (enddate is result of certain calculations).

What i am tryning is this :-

for D in `cat file`;do
str1=`echo $D|cut -c1-15`
date1=`echo $D|cut -c16-23`
date2=`echo $D|cut -c24-31`
str2=`echo $D|cut -c32-`
enddate=$enddate
D=$str1$enddate$enddate$str2
done

This is not working.
Can someone please tell me an alternate method, using sed or awk. And also tell me why is this not working.

Code:

sed "s/20070416/$enddate/g" file > temp
mv temp file

Code:

for D in `cat file`;do
str1=`echo $D|cut -c1-15`
date1=`echo $D|cut -c16-23`
date2=`echo $D|cut -c24-31`
str2=`echo $D|cut -c32-`
enddate=$enddate
echo $str1$enddate$enddate$str2 >> temp
done
mv temp file

[QUOTE=anbu23;302127633]

Code:

sed "s/20070416/$enddate/g" file > temp
mv temp file

This will not work for me, as i cannot give the string 20070416 and replace it with $enddate as this string is not fixed. It will keep changing everyday.

And sed "s/$date1/$enddate/g" file > temp does not work

Code:

for D in `cat file`;do
str1=`echo $D|cut -c1-15`
date1=`echo $D|cut -c16-23`
date2=`echo $D|cut -c24-31`
str2=`echo $D|cut -c32-`
enddate=$enddate
echo $str1$enddate$enddate$str2 >> temp
done
mv temp file

[/QUOTE]

I have already tried this option. For some reason, I am getting repeated data. What i mean is, if there are three rows in file then there are 39 rows in temp. The three rows are repeated 13 times.
I am not able to understand why is this happening.

Code:

sed "s/20070416/$enddate/g" file > temp
mv temp file

Hey i tried again, the code sed "s/$date1/$enddate/g" works fine. I did some mistake earlier.
Thanks a lot for all your help!!!