Counter increment in Bash loop not working

Question

I have the following simple script where I am running a loop and want to maintain a COUNTER. I am unable to figure out why the counter is not updating. Is it du

Answer 1

Source script has some problem with subshell. First example, you probably do not need subshell. But We don't know what is hidden under "Some more action". The most popular answer has hidden bug, that will increase I/O, and won't work with subshell, because it restores couter inside loop.

Do not fortot add '\' sign, it will inform bash interpreter about line continuation. I hope it will help you or anybody. But in my opinion this script should be fully converted to AWK script, or else rewritten to python using regexp, or perl, but perl popularity over years is degraded. Better do it with python.

Corrected Version without subshell:

#!/bin/bash
WFY_PATH=/var/log/nginx
WFY_FILE=error.log
COUNTER=0
grep 'GET /log_' $WFY_PATH/$WFY_FILE | grep 'upstream timed out' |\
awk -F ', ' '{print $2,$4,$0}' |\
awk '{print "http://example.com"$5"&ip="$2"&date="$7"&time="$8"&end=1"}' |\
awk -F '&end=1' '{print $1"&end=1"}' |\
#(  #unneeded bracket
while read WFY_URL
do
    echo $WFY_URL #Some more action
    COUNTER=$((COUNTER+1))
done
# ) unneeded bracket

echo $COUNTER # output = 0

Version with subshell if it is really needed

#!/bin/bash

TEMPFILE=/tmp/$$.tmp  #I've got it from the most popular answer
WFY_PATH=/var/log/nginx
WFY_FILE=error.log
COUNTER=0
grep 'GET /log_' $WFY_PATH/$WFY_FILE | grep 'upstream timed out' |\
awk -F ', ' '{print $2,$4,$0}' |\
awk '{print "http://example.com"$5"&ip="$2"&date="$7"&time="$8"&end=1"}' |\
awk -F '&end=1' '{print $1"&end=1"}' |\
(
while read WFY_URL
do
    echo $WFY_URL #Some more action
    COUNTER=$((COUNTER+1))
done
echo $COUNTER > $TEMPFILE  #store counter only once, do it after loop, you will save I/O
)

COUNTER=$(cat $TEMPFILE)  #restore counter
unlink $TEMPFILE
echo $COUNTER # output = 0