Delete old remote branches in git using `git push --delete origin`

delete-old-remote-branches.sh

#!/usr/bin/env bash

# if the most recent commit on the branch is older than MAX_AGE_DAYS, then the branch
# will be deleted.
MAX_AGE_DAYS=180
# if DRY_RUN=1, then only print the names of the branches that would be deleted.
if [ -z "$DRY_RUN" ]; then
    DRY_RUN=0
fi

for branch in $(git branch -a); do
    if echo $branch | grep "remotes/origin" &>/dev/null; then
        b=$(echo $branch | sed 's/remotes\/origin\///g')
    else
        continue
    fi

    # protected branches
    if [[ $b == "master" ]]; then continue; fi
    if [[ $b == "mainline" ]]; then continue; fi
    if [[ $b == "main" ]]; then continue; fi
    if [[ $b == "dev" ]]; then continue; fi
    if [[ $b == "HEAD" ]]; then continue; fi

    # skip branch if there is some problem checking it out
    if ! git checkout $b &>/dev/null; then continue; fi

    if (($(git log -1 --format=%ct) < $(date -d "-$MAX_AGE_DAYS days" +%s))); then
        if [ $DRY_RUN -ne 0 ]; then
            echo "dry run: would delete branch $b"
        else
            git push --delete origin $b
        fi
    fi
done