Let's consider a scenario where you need to join or merge lines of data from two different variables. In this example, let's consider two variables that have lines you want to merge.

foo="Employee, name=John Doe, occupation=Engineer"
bar="Employee, name=John Doe, department=IT Infrastructure"

First, you will need to create unique variable for each field of data in each variable. 

name=$(echo $foo | awk -F',' '{print $2}')
occupation=$(echo $foo | awk -F',' '{print $3}')
department=$(echo $bar | awk -F',' '{print $3}')

Then, you probably will want to create a new variable that contains the merged data.

result=$(echo $name $occupation $department)

In this example, the $result variable will contain the following data.

John Doe occupation=Engineer department=IT Infrastructure

Multiple lines

Additional logic is needed when you are working with variables that contain two or more lines of data.

foo="
Employee, name=John Doe, occupation=Engineer
Employee, name=Jane Doe, occupation=Sales Manager
"

bar="
Employee, name=John Doe, department=IT Infrastructure
Employee, name=Jane Doe, department=Sales
"

The following script demonstrates the logic.

#!/bin/bash

foo="
Employee, name=John Doe, occupation=Engineer
Employee, name=Jane Doe, occupation=Sales Manager
"

bar="
Employee, name=John Doe, department=IT Infrastructure
Employee, name=Jane Doe, department=Sales
"

# Tell bash to split at newline
IFS=$'\n'

# Create an empty variable that will contain the merged data
merged=""

# Loop through the first variable ($foo in this example)
for line in $foo
do

  # Create unique variable for each field of data from each line in the $foo variable
  foo_name=$(echo $line | awk -F',' '{print $2}')
  occupation=$(echo $line | awk -F',' '{print $3}')

  # Loop through the second variable ($bar in this example)
  for data in $bar
  do

    # Create unique variable for each field of data from each line in the $bar variable
    bar_name=$(echo $data | awk -F',' '{print $2}')
    department=$(echo $data | awk -F',' '{print $3}')

    # This if statement is used so that we only process lines in $foo and $bar that contain the same name
    if [[ $line =~ $bar_name ]]; then

      # Create a new variable that contains the merged data from $foo and $bar
      merged+="$foo_name, $occupation, $department"

      # Add a new line
      merged+=$'\n'
    fi
  done
done 

# Loop through each line
for line in $merged
do
  echo $line
done

# Cleanup
unset IFS

Running this script will produce a variable that contains the merged data.

name=John Doe, occupation=Engineer, department=IT Infrastructure
name=Jane Doe, occupation=Sales Manager, department=Sales