right now my aim is to scan a single ip and get only the open ports printed in a single line seperated by commas.
The code below does that but it inject % at the end
The goal is to achieve port number in a single line as output without the last 2 characters (the last comma and % sign)

sudo nmap -vv -sS 10.129.208.16 -oG  - | awk -v OFS=':' '
/open/ {
  for (i=4;i<=NF;i++) {
    split($i,a,"/");
    if (a[2]=="open") {printf a[1]","}
  }
}'

output :
21,22,53,80,139,443,445,%

required output:
21,22,53,80,139,443,445