Prune local branches that were merged into a remote GitHub repo using squash commits.

prune_merged_branches.sh

#!/bin/bash

# This script looks for local branches which have an upstream branch set, but
# where said upstream branch no longer exists.  The implication here is that the
# engineer pushed the branch to GitHub (to send a PR for review), merged the PR,
# and (auto-)deleted the remote branch.
#
# The script asks for confirmation before deleting the local branches as this is
# destructive, and could cause someone to lose work if a branch gets into this
# state without its contents actually having been merged upstream.

to_delete=""
for branch in $(git branch); do
  if [[ "$branch" = "*" ]]; then
    continue
  fi
  # Get the ref name for the branch.
  ref=$(git rev-parse --symbolic-full-name $branch)
  # Check if there is an upstream branch.  If not, it's likely a PR has not been
  # created for this branch yet.
  upstream=$(git for-each-ref --format='%(upstream:short)' $ref)
  if [[ -z "$upstream" ]]; then
    continue
  fi
  # Query the remote for the upstream branch.  If it no longer exists, this is
  # probably the local branch for a PR that was merged upstream.
  remote_branch=$(git ls-remote --heads origin $ref)
  if [[ -z "$remote_branch" ]]; then
    to_delete="$to_delete $branch"
  fi
done

if [[ -z "$to_delete" ]]; then
  echo "No local branches need pruning."
else
  echo "Found local branches to prune: "
  echo ""
  for branch in $(echo ${to_delete}); do
    echo "  $branch"
  done
  echo ""
  # Ask the user for confirmation before taking an action.
  read -p "Do you want to delete these local branches? (y/N) " -r
  echo ""
  if [[ $REPLY =~ ^([Yy]|YES|yes)$ ]]; then
    # The user said yes, so forcibly delete the local branches in question.
    git branch -D $to_delete
    retval=$?
    echo ""
    if [[ $retval -eq 0 ]]; then
      echo "Branches deleted."
    else
      echo "One or more errors occurred while trying to delete branches."
      echo "Some of the listed branches may have been deleted; please consult stderr output."
      exit $retval
    fi
  else
    echo "Cancelled."
  fi
fi