Delete merged git branches locally and on remote

git-rm-merged

#!/bin/bash
# Remove merged git branches locally and on remote(s)

set -e

# Script constants
BRANCH_WHITELIST="(\*|master|other-special-branches)"
REMOTES="origin"  # Add more remotes here as space-separated list

echo "Deleting merged branches locally"
git branch --merged master \
    | egrep -v "$BRANCH_WHITELIST" \
    | xargs -r git branch -d

# Delete merged branches from each remote.
for remote in $REMOTES; do
    echo "Deleting merged branches from $remote"
    git fetch "$remote" --prune
    for branch in $(git branch -r --merged master \
                        | grep "$remote" \
                        | egrep -v "$BRANCH_WHITELIST"); do
        git push "$remote" --delete "${branch#*/}"
    done
done

To run this script on macOS, you need to first install the GNU version of xargs via brew install findutils, then change line 13 to call gxargs (or update your PATH so that the GNU version of xargs comes before the BSD version).

is there is any harm if I delete merged branches from a fork?
and, if I do the same for unmerged (old, stalled) branches also?
and if I deleted a branch can I put it back again in the fork from upstream? how? Thanks!

No particular harm no, the changes you make to a fork are completely independent of the changes to the upstream. Obviously if you delete an unmerged branch that you created in your fork and isn't mirrored in the upstream, you won't (easily) be able to get it back.

Sure you can pull a branch from upstream into your branch, you just need to pull it from upstream to your local repo first and then push it to your fork. Assuming you have the fork remote set up as "origin" and the upstream set up as "upstream" (git remote add upstream <upstream URL> if you don't have that):

git fetch upstream/branchname
git checkout branchname
git push -u origin branchname

@ryanc414 Thanks a lot!