awk -F '' '{
l=length($0)
for(i=1;i<=l;i++){
printf $i
if((l-i)%3==0 && i!=l){
printf ","
}
}
print ""
}' nowcoder.txt
awk -F '' '{
l=length($0)
for(i=1;i<=l;i++){
printf $i
if((l-i)%3==0 && i!=l){
printf ","
}
}
print ""
}' nowcoder.txt