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Combining and summing data from multiple files
aaa 5
bbb 2
ccc 9
ddd 46
eee 89
fff 56

aaa 54
bbb 8
ccc 16
ddd 4
eee 66
fff 9

declare -A sums
while read name val1 val2; do
  sums[$name]=$(( val1 + val2 ))
done < <(join -j 1 file1 file2)

echo "Sum of aaa: ${sums[aaa]}"
echo "Sums of ccc and ddd: $(( ${sums[ccc]} + ${sums[ddd]} ))"
echo "Sums of bbb, eee, and fff: $(( ${sums[bbb]} + ${sums[eee]} + ${sums[fff]} ))"

kent$  awk 'NR==FNR{a[$1]=$2;next;}{a[$1]+=$2}END{print "sum of aaa:",a["aaa"]}' file1 file2
sum of aaa: 59

awk '{a[$1]+= $2;}END{for(i in a){print i,a[i];}}' file

cat file1 file2 | awk '...