Delete all merged branches from the remote Git repository (assuming master is the main branch)

delete_merged_git_branches_remotely

# Sources: https://community.atlassian.com/t5/Bitbucket-questions/Is-there-a-way-to-delete-branches-in-bulk/qaq-p/547331

# Make sure remotes are up to date (with stale remotes purged):
git fetch -p
 
# Initial no-op run --- do the branches to delete look correct?
# Be careful to omit 'master' from the output.
git branch --remote --merged origin/master | grep -v 'master' | cut -b 10- | xargs

# Do the bulk delete!!!  (can take a long time...)
git branch --remote --merged origin/master | grep -v 'master' | cut -b 10- | xargs git push --delete origin