Merge two files using shell scripting

Question

I have two files say File A and File B. I want to merge the two files as shown below.

File A

Data A
a 123
b 35
-------
Data B
-------
Data C
a 234
d 23

File B

Data A
a 12
c 1
-------
Data B
-------
Data C    
d 24

Output should be

Data A
a 135
b 35
c 1
-------
Data B
-------
Data C
a 234    
d 47

Data A,Data ... will be in the same order for both the files and the variables under Data A, Data ... will also be alphabetically sorted for both the files but some variable may be there in one file or may not.

I tried to outer join the two files for every block (delimiter as ----) and then add the two numbers but i couldn't think of any way to do it.

Answer 1

Should be probably done in some real programming language but you asked for a bash so here it goes:

#!/bin/bash

declare -A data

read_sect_from_fd() {
    local fd=$1
    while read -u $fd -r var val; do
        [[ $var == ------- ]] && break
        if [ "${data[$var]}" ]; then
            data[$var]=$(( $val + ${data[$var]} ))
        else
            data[$var]=$val
        fi
    done <&3
}

print_sect() {
    for i in "${!data[@]}"; do
        echo "$i ${data[$i]}"
    done
}

exec 3<"File A"
exec 4<"File B"

while IFS= read -u 3 -r heading ; do
    read_sect_from_fd 3
    IFS= read -u 4 -r heading
    read_sect_from_fd 4
    [ "$not_first" ] && echo "-------"
    not_first=1
    echo "$heading"
    print_sect
    data=()
done