[am]king ~/a/tm$ sort first.csv > first.s
[am]king ~/a/tm$ sort second.csv > second.s
[am]king ~/a/tm$ join -v1 -t, first.s second.s
carrot,6
[am]king ~/a/tm$ join -v2 -t, first.s second.s
banana,yellow
pea,brown
spinach,green