I know the ? is for something like
(condition) ? statement-1: statement-2
but, in this case I am not understanding how a[FNR]=a[FNR] is working, when is this false?
awk '{a[FNR]=a[FNR] ? a[FNR]","$0 : $0} END{for(i=1;i<=FNR;i++)print a[i]}' *.csv
question from:https://stackoverflow.com/questions/65931608/what-is-the-meaning-of-afnr-afnrafnr-00-in-awk