gistfile1.sh

#!/bin/bash

if [[ $1 != "-f" ]]; then
    echo "### Dry-run mode, specify -f to actually perform deletes.";
fi;
for branch in $(git branch -r --merged origin/master | grep '\<origin/' | grep -v '\<origin/master\>');
do
    if [[ -z $(git rev-list $branch --since '1 month') ]]; then
        name=$(echo $branch | sed 's/^origin\///');
        if [[ $1 = "-f" ]]; then
            git push --delete origin "$name";
        else
            echo git push --delete origin "$name";
        fi;
    fi;
done