#!/bin/bash

function branches { git for-each-ref --format="%(refname:short)" "$@"; }

git fetch --all --quiet
mapfile -t branches < <( branches refs/heads )
for i in "${branches[@]}"; do
    [ "$DEBUG" ] && printf "Checking branch <%s>\n" "$i"
    mapfile -t others < <( branches refs/{heads,remotes/\*}/"$i" )
    [ "$DEBUG" ] && printf "Across remotes:" && printf " <%s>" "${others[@]}" && printf "\n"
    mapfile -t bases < <( git merge-base --octopus --all "${others[@]}" )
    [ "$DEBUG" ] && printf "Merge bases:" && printf " <%s>" "${bases[@]}" && printf "\n"
    git log --graph --oneline --boundary "${others[@]}" --not "${bases[@]}"
done