replacing column 3 in csv

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http://www.unix.com – sample csv 1234,abc,000,def, 5678,abc,010,def, 9012,abc,020,def, desired output 1234,abc,0,def, 5678,abc,1,def, 9012,abc,2,def, I need to change only the 2nd column from 000 to 0, 010 to 1 and 020 to 2 in shell. I tried using awk -F with if condition in column 3. It din help me (HowTos)