This is a simple version of the Unix tool
cut
go run main.go -f 2 sample.tsv
go run main.go -f 1 -d , fourchords.csv | head -n5
go run main.go -f '1 2' sample.tsv
go run main.go -f 1,2 sample.tsv
go run main.go -d , -f "1 2" fourchords.csv | head -n5
tail -n5 fourchords.csv | go run main.go -d , -f 1,2
tail -n5 fourchords.csv | go run main.go -d , -f 1,2 -
go run main.go -f 2 -d , fourchords.csv | uniq | wc -l