Very rough script that cleans up all old branches that are loosely hanging around after a while. Also updates the origin remote.

git-cleanup.sh

#!/bin/sh

fix_branch_output () {
    # Strips first columns from the output, to remove whitespace and "current
    # branch" marker from git-branch's output
    cut -c 3-
}

local_branches () {
    git branch | fix_branch_output
}

remote_branches () {
    git branch -r | grep -v ' -> ' | fix_branch_output
}

all_branches () {
    local_branches
    remote_branches
}

filter_nontrunks () {
    #grep -vEe '(^|/)(master|develop|trunk|production)$'
    grep -vEe '^(origin/)?master$'
}

branches () {
    all_branches | filter_nontrunks
}

to_sha () {
    git show | awk "NR==1 {print \$2}"
}

startswith() { [ "$1" != "${1#$2}" ]; }

base_master=$(git merge-base "master" "origin/master")

for branch in `branches`; do
    echo "$branch... \c"
    #if is_ancestor "$branch" master; then
    branch_sha=$(git rev-parse "$branch")
    base=$(git merge-base "$branch" "$base_master")
    if [ "$base" == "$branch_sha" -a "$base" != "$base_master" ]; then
        echo "OK"
        git branch -d "$branch"
        if startswith "$branch" origin/; then
            git push origin --delete "${branch#origin/}"
        fi
    else
        echo "SKIP"
    fi
done