Adding column values from multiple different files - bash

Question

I have ~100 files and I would like to do an arithmetical operation (e.g. sum them up) on the second column of the files, such that I add the value of first row of one file to the first row value of second file and so on for all rows of column 2 in each file.
In my actual files I have ~30 000 rows so any kind of manual manipulation with the rows is not possible.
fileA
1 1
2 100
3 1000
4 15000
fileB
1 7
2 500
3 6000
4 20000
fileC
1 4
2 300
3 8000
4 70000
output:
1 12
2 900
3 15000
4 105000
I used this and ran it as: script.sh listofnames.txt (All the files have the same name but they are in different directories so I was referring to them with $line to the file with the list of directories names). This gives me a syntax error and I am looking for a way to define the "sum" otherwise.
while IFS='' read -r line || [[ -n "$line" ]]; do
awk '{"'$sum'"+=$3; print $1,$2,"'$sum'"}' ../$line/file.txt >> output.txt
echo $sum
done < "$1"

Answer 1

$ paste fileA fileB fileC | awk '{sum=0; for (i=2;i<=NF;i+=2) sum+=$i; print $1, sum}'
1 12
2 900
3 15000
4 105000
or if you wanted to do it all in awk:
$ awk '{key[FNR]=$1; sum[FNR]+=$2} END{for (i=1; i<=FNR;i++) print key[i], sum[i]}' fileA fileB fileC
1 12
2 900
3 15000
4 105000
If you have a list of directories in a file named "foo" and every file you're interested in in every directory is named "bar" then you can do:
IFS=$'\n' files=( $(awk '{print $0 "/bar"}' foo) )
cmd "${files[#]}"
where cmd is awk or paste or anything else you want to run on those files. Look:
$ cat foo
abc
def
ghi klm
$ IFS=$'\n' files=( $(awk '{print $0 "/bar"}' foo) )
$ awk 'BEGIN{ for (i=1;i<ARGC;i++) print "<" ARGV[i] ">"; exit}' "${files[#]}"
<abc/bar>
<def/bar>
<ghi klm/bar>
So if your files are all named file.txt and your directory names are stored in listofnames.txt then your script would be:
IFS=$'\n' files=( $(awk '{print $0 "/file.txt"}' listofnames.txt) )
followed by whichever of these you prefer:
paste "${files[#]}" | awk '{sum=0; for (i=2;i<=NF;i+=2) sum+=$i; print $1, sum}'
awk '{key[FNR]=$1; sum[FNR]+=$2} END{for (i=1; i<=FNR;i++) print key[i], sum[i]}' "${files[#]}"