Cleanup remote branches not merged with "development" that are stale for 4 weeks. But don't clean master

git branch cleanup

#!/bin/bash                                                                                                             
                                                                                                                        
LOG="tee -a /tmp/branch-cleanup.log"                                                                                    
                                                                                                                        
git checkout development                                                                                                
git fetch                                                                                                               
git remote prune origin                                                                                                 
                                                                                                                        
branchlist=`git branch -r --merged development | sed 's/ *origin\///' | grep -v 'master$' | grep -v 'development$'`        
                                                                                                                        
for branch in $branchlist                                                                                               
do                                                                                                                      
    commitHappendInTheLast4Weeks=`git log -n1 --since="4 weeks ago" "origin/"$branch`                                   
    if [ "$commitHappendInTheLast4Weeks" == "" ]                                                                        
    then                                                                                                                
        echo "To be deleted: "$branch | $LOG                                                                            
        echo `git log -n1 "origin/"$branch` | $LOG                                                                      
        git push origin ":"$branch | $LOG                                                                               
    fi                                                                                                                  
done