Basic way to build up generating of git stats with bash with JSON output. Just an example...

git_stats.sh

#!/bin/bash

# echo "## Each files last update, sorted from oldest to newest"
# cd .. && git ls-tree -r --name-only HEAD | while read filename; do   echo "$(git log -1 --format="%aI" -- $filename) $filename"; done | sort -rk1

function lastCommit {
    git log -1 --format=%cI
}

function addNumber {
    echo $content | jq '. += {"'"$1"'": '"$2"'}'
}

function addString {
    echo $content | jq '. += {"'"$1"'": "'"$2"'"}'
}

function addStringList {
    data=$($2)
    IFS=$'\n' read -d "" -r -a items <<<"$data"

    content=$(echo $content | jq '. += {"'"$1"'": []}')
    for i in "${items[@]}"; do
        content=$(echo $content | jq '.'"$1"' +=  ["'"$i"'"]')
    done

    echo $content
}

function topCommitters {
    git shortlog -sn --no-merges --all
}

function linesChanged {
    # 2 months, 6 months and all time for all stats
    # have a flag of content that's missing or not updated in X time
    previousTimeframe="2 months"
    d=$(date -d "$previousTimeframe ago" "+%b %d %Y" | tr [:lower:] [:upper:])
    IFS=$'\n'

    for i in $(git shortlog -sn --no-merges --since "$d"); do
    name=$(echo $i | awk '{printf("%s %s\n",$2,$3)}')

    printf "$name = "
    git log --numstat --pretty="%H" --author=$name --since "$d" | awk 'NF==3 {plus+=$1; minus+=$2} END {printf("+%d, -%d\n", plus, minus)}'
    done
}

content='{}'
content=$(addString "last_commit" $(lastCommit))
content=$(addNumber "number_of_x" 12)
content=$(addStringList "top_committers" "topCommitters")
content=$(addStringList "lines_changed_in_last_2_months" "linesChanged")
echo $content | jq .