This will 'delete' (git branch -D) all branches containing a substring (prefix) that are already merged to origin/master

cleanup-local-branches.sh

#!/bin/sh
# Created by richmondwang
# Required: bash4, git1.7, sed, awk, grep
# 
# This will 'delete' (git branch -dl) all branches 
# containing a substring (prefix) that are already merged to origin/master

prefix="feature/richmond/"
# only delete my own branches

if [ "$1" != "" ]; then
	prefix=$1
	# or specify a prefix as argument
fi

currentBranch=$(git branch | grep "*" | awk '{print $2;}')
git checkout master

IFS=" " read -r -a branches <<< $(git branch -r --no-merged | grep ${prefix} | sed 's/\// /' | awk '{print $2;}' | sed -e ':a' -e 'N' -e '$!ba' -e 's/\n/ /g')
# get all existing branches in remote

localBranches=$(git branch | grep ${prefix} | sed -e ':a' -e 'N' -e '$!ba' -e 's/\n  / /g')
# get all local branches

deleted=$localBranches
for branch in ${branches[@]}; do
	# loop and delete one by one
    deleted=$(sed "s!${branch}!!" <<< ${deleted})
done

if [ "$deleted" == "" ]; then
	echo "Nothing to delete, you local is clean."
else
	git branch -dl ${deleted}
fi
git checkout $currentBranch
# checkout where you last checked out