How to read from two files in the same time shell

Question

I have two files,

A

john 1 2 3 4 5 6 7
Ely 10 9 9 9 9 9 9
Maria 3 5 7 9 2 1 4
Rox 10 10 10 10 10 10 10

B 
john 7.5
Ely 4.5
Maria 3,7
Rox 8.5

Answer 1

If you really want to read two files at the same time (which doesn't appear to be your actual question -- join is indeed the right tool for what you're doing), you can open them on different FDs:

while IFS= read -r -u 4 line1 && IFS= read -r -u 5 line2; do
  echo "Line from first file: $line1"
  echo "Line from second file: $line2"
done 4<file1 5<file2

Answer 2

Use the join command to combine A and B into a single file C:

$ join A.txt B.txt
john 1 2 3 4 5 6 7 7.5
Ely 10 9 9 9 9 9 9 4.5
Maria 3 5 7 9 2 1 4 3,7
Rox 10 10 10 10 10 10 10 8.5

It should be simple to modify your current script to process the data in this form.