regex - How to read content from two files and merge into a 3rd file in bash shell -

How do you read / process 2 files in sync with each other in sync?

I have 2 text files in which they have the same line numbers / items in one file

  ABC   
 is another file   
 
  1 2 3   
 How can I loop through sync in these files so that  a   1 , b-> 2, c-> 3?  
 I thought that I can read files as an array and then process them with an index but it seems that my syntax / argument is wrong.  
 By doing this,  f1 = $ (cat File1)  creates  f1 = abc . I thought that  f1 = ($ (cat file1)) will make it in an array, but it creates  f1 = a  and thus there is no array to process for me is not.  
 If someone was wondering what my wrong code is:  
  hostnames = ($ (cat $ host_file)) # trying to read as an array For obviously the wrong roles = ($ (cat $ role_file)) I echo $ {hostname {$ i]} in {0..3} # again through file / array # element in each element , But instead of N, only one object is objects $ {rolls [$ i]}    
 
 
 Use  paste Not  () to combine the files, then the process of a line of joint file at a time:  
  paste file1 file2 | While reading -r first second do the first resonant $ second