Variable loss in redirected bash while loop - bash

Question

I have the following code
for ip in $(ifconfig | awk -F ":" '/inet addr/{split($2,a," ");print a[1]}')
do
bytesin=0; bytesout=0;
while read line
do
if [[ $(echo ${line} | awk '{print $1}') == ${ip} ]]
then
increment=$(echo ${line} | awk '{print $4}')
bytesout=$((${bytesout} + ${increment}))
else
increment=$(echo ${line} | awk '{print $4}')
bytesin=$((${bytesin} + ${increment}))
fi
done < <(pmacct -s | grep ${ip})
echo "${ip} ${bytesin} ${bytesout}" >> /tmp/bwacct.txt
done
Which I would like to print the incremented values to bwacct.txt, but instead the file is full of zeroes:
91.227.223.66 0 0
91.227.221.126 0 0
127.0.0.1 0 0
My understanding of Bash is that a redirected for loop should preserve variables. What am I doing wrong?

Answer 1

First of all, simplify your script! Usually there are many better ways in bash. Also most of the time you can rely on pure bash solutions instead of running awk or other tools.
Then add some debbuging!
Here is a bit refactored script with debugging
#!/bin/bash
for ip in "$(ifconfig | grep -oP 'inet addr:\K[0-9.]+')"
do
bytesin=0
bytesout=0
while read -r line
do
read -r subIp _ _ increment _ <<< "$line"
if [[ $subIp == "$ip" ]]
then
((bytesout+=increment))
else
((bytesin+=increment))
fi
# some debugging
echo "line: $line"
echo "subIp: $subIp"
echo "bytesin: $bytesin"
echo "bytesout: $bytesout"
done <<< "$(pmacct -s | grep "$ip")"
echo "$ip $bytesin $bytesout" >> /tmp/bwacct.txt
done
Much clearer now, huh? :)