Simple command to test if a branch was squashed/rebased and then merged into another. Not tested very much.

exampleUsage.bash

#! /usr/bin/env bash

merged=()
unmerged=()

for branch in $(git for-each-ref --format="%(refname:short)" refs/heads); do
	if wasBranchMerged "$branch" staging; then
		merged+=("$branch")
	else
		unmerged+=("$branch")
	fi
done

echo "Okay to delete:"
echo "${merged[*]}"

echo "Hang on to:"
echo "${unmerged[*]}"

wasBranchMerged.bash

#! /usr/bin/env bash

wasBranchMerged() {
	local branch="$1"
	local targetBranch="$2"

	local searchString="Merge branch '$branch' into '$targetBranch'"

	 git log --oneline --merges "$targetBranch" | grep -q "$searchString"
}