matching file problem
hi
I need help for matching two files
a.txt
123,20080921,2419,ec1,20081021
456,20080923,2420,ec1,20081021
789,20080920,2419,ec1,20081021
124,20080921,2421,ec1,20081023
125,20080921,2419,ec1,20081021
126,20080921,2419,ec1,20081021
128,20080921,2419,ec1,20081021
b.txt
123,20080922,2419,ec1,20081021
456,20080923,2420,ec1,20081021
789,20080920,2418,ec1,20081021
124,20080921,2421,ec2,20081023
125,20080921,2419,ec1,20081021
126,20080921,2419,ec1,20081021
129,20080921,2419,ec1,20081021
I want to compare both files
i want the line of first file which is different from 2nd file in any of the field
like here first line differ in 2nd coloum value
simirly 3rd line differ in 3rd coloum value
last line is not in list so it should also come in output
output will be like
c.txt
123,20080921,2419,ec1,20081021
789,20080920,2419,ec1,20081021
124,20080921,2421,ec1,20081023
125,20080921,2419,ec1,20081021
126,20080921,2419,ec1,20081021
128,20080921,2419,ec1,20081021
these all line have atleast different value.
pls help ....