sort 差集
sort -m <(sort big.csv | uniq) <(sort small.csv | uniq) <(sort small.csv | uniq) | uniq -u > final.csv
grep 交集
grep -F -f big.csv small.csv > union_set.csv
grep 差集
# 注意，是 big - small 的結果
grep -F -v -f small.csv big.csv > difference_set.csv