Linux – How do I get results from background process linux shell scripts?

For example, suppose I want to count the number of lines of 10 large files and print the total number.

for f in files
do
    #this creates a background process for each file
    wc -l $f | awk '{print $1}' &
done

I’m trying something like this :

for f in files
do
    #this does not work :/
    n=$( expr $(wc -l $f | awk '{print $1}') + $n ) &
done

echo $n

I finally found a working solution using anonymous pipes and bash :

#!/bin/bash

# this executes a separate shell and opens a new pipe, where the 
# reading endpoint is fd 3 in our shell and the writing endpoint
# stdout of the other process. Note that you don't need the 
# background operator (&) as exec starts a completely independent process.
exec 3< <(./a.sh 2&1)

# ... do other stuff

# write the contents of the pipe to a variable. If the other process
# hasn't already terminated, cat will block.
output=$(cat <&3)