csv.sh

#! /bin/bash

decimal=243881281

function dec2ip {
        local v=$1
        local i1=$((v>>24 & 255))
        local i2=$((v>>16 & 255))
        local i3=$((v>>8  & 255))
        local i4=$((v & 255))
        printf '%d.%d.%d.%d\n' $i1 $i2 $i3 $i4
}

data=$'243881281,243881281\n243881282,243881282\n243881283,243881283'
echo "\$IFS: $IFS"

printf $"ip1, ip2\n$(
echo "$data" | while IFS=, read -r ip1 ip2; do
        echo "$(dec2ip $ip1), $(dec2ip $ip2)"
done)" > output.csv

#while IFS=\n, read -r field1 field2
#do
#       echo "field1: $field1, field2: $field2"
#       #echo "$(dec2ip field1), $(dec2ip field2)"
#done <<< $data

dec2ip $decimal