i have two files and i want to compare these two
it shoud print those lines which are not in 2nd file
a.txt
1236,AB,0
2345,CD,1
5679,EF,1
9123,AA,1
9223,AA,0

b.txt
1234,AB,0
2345,CD,1
5678,EF,1
9123,AA,0
o/p
1236,AB,0
5679,EF,1
9123,AA,1
9223,AA,0