awk - send sum to global variable - linux

Question

I have a line in a bash script that calculates the sum of unique IP requests to a certain page.
grep $YESTERDAY $ACCESSLOG | grep "$1" | awk -F" - " '{print $1}' | sort | uniq -c | awk '{sum += 1; print } END { print " ", sum, "total"}'
I am trying to get the value of sum to a variable outside the awk statement so I can compare pages to each other. So far I have tried various combinations of something like this:
unique_sum=0
grep $YESTERDAY $ACCESSLOG | grep "$1" | awk -F" - " '{print $1}' | sort | uniq -c | awk '{sum += 1; print ; $unique_sum=sum} END { print " ", sum, "total"}'
echo "${unique_sum}"
This results in an echo of "0". I've tried placing __$unique_sum=sum__ in the END, various combinations of initializing the variable (awk -v unique_sum=0 ...) and placing the variable assignment outside of the quoted sections.
So far, my Google-fu is failing horribly as most people just send the whole of the output to a variable. In this example, many lines are printed (one for each IP) in addition to the total. Failing a way to capture the 'sum' variable, is there a way to capture that last line of output?
This is probably one of the most sophisticated things I've tried in awk so my confidence that I've done anything useful is pretty low. Any help will be greatly appreciated!

Answer 1

You can't assign a shell variable inside an awk program. In general, no child process can alter the environment of its parent. You have to have the awk program print out the calculated value, and then shell can grab that value and assign it to a variable:
output=$( grep $YESTERDAY $ACCESSLOG | grep "$1" | awk -F" - " '{print $1}' | sort | uniq -c | awk '{sum += 1; print } END {print sum}' )
unique_sum=$( sed -n '$p' <<< "$output" ) # grab the last line of the output
sed '$d' <<< "$output" # print the output except for the last line
echo " $unique_sum total"
That pipeline can be simplified quite a lot: awk can do what grep can do, so first
grep $YESTERDAY $ACCESSLOG | grep "$1" | awk -F" - " '{print $1}'
is (longer, but only one process)
awk -F" - " -v date="$YESTERDAY" -v patt="$1" '$0 ~ date && $0 ~ patt {print $1}' "$ACCESSLOG"
And the last awk program just counts how many lines and can be replaced with wc -l
All together:
unique_output=$(
awk -F" - " -v date="$YESTERDAY" -v patt="$1" '
$0 ~ date && $0 ~ patt {print $1}
' "$ACCESSLOG" | sort | uniq -c
)
echo "$unique_output"
unique_sum=$( wc -l <<< "$unique_output" )
echo " $unique_sum total"