Shell Script to Manipulate NETMASK/CIDR

a_cidr_netmask.sh

#!/bin/bash
# from https://stackoverflow.com/questions/20762575/explanation-of-convertor-of-cidr-to-netmask-in-linux-shell-netmask2cdir-and-cdir
# see also https://gist.github.com/RichardBronosky/7902f062ab36d3c99413ba21986ed0cb
mask2cdr ()
{
   # Assumes there's no "255." after a non-255 byte in the mask
   local x=${1##*255.}
   set -- 0^^^128^192^224^240^248^252^254^ $(( (${#1} - ${#x})*2 )) ${x%%.*}
   x=${1%%$3*}
   echo $(( $2 + (${#x}/4) ))
}

cdr2mask ()
{
   # Number of args to shift, 255..255, first non-255 byte, zeroes
   set -- $(( 5 - ($1 / 8) )) 255 255 255 255 $(( (255 << (8 - ($1 % 8))) & 255 )) 0 0 0
   [ $1 -gt 1 ] && shift $1 || shift
   echo ${1-0}.${2-0}.${3-0}.${4-0}
}

function join_by {
  local d=${1-} f=${2-}
  if shift 2; then
    printf %s "$f" "${@/#/$d}"
  fi
}

JS=()
while read -r LINE || [ -n "$LINE" ]; do 
    JS+=('{
            "val": "'"$LINE"'",
            "note": "CN"
        }')
done <<< "$(grep ' bypass4' ipset.conf  |awk '{print $3}')"

join_by ',' "${JS[@]}" 

JS=()
while read -r LINE || [ -n "$LINE" ]; do 
    #echo "$LINE";
    IFS='/' read -ra ARR <<< "$LINE"
    NET=${ARR[0]} 
    MASK=${ARR[1]}
    CIDR=$(mask2cdr "$MASK")
    JS+=('{
            "val": "'"$NET"/"$CIDR"'",
            "note": "NCN"
        }')
done <<< "$(awk '{print $3}' < cn-no-route1.txt)"

join_by ',' "${JS[@]}"  

cn-no-route1.txt

no-route = 1.0.0.0/255.128.0.0

ipset.conf

add bypass4 140.237.0.0/16 comment "force-bypass-ips"

see also https://gist.github.com/RichardBronosky/7902f062ab36d3c99413ba21986ed0cb