Rebuild an integration branch from master and reapply branches previously merged into integration but that have not been merged to master

integrate.sh

#!/usr/bin/env bash

# Update the origin remote and prune it
updateOrigin()
{
    git fetch origin
    git remote prune origin
}

# List branches that are merged into integration, but not master
listBranches()
{
    comm -12 \
        <(git branch -r --no-merged origin/master | sort -d | grep origin) \
        <(git branch -r --merged origin/integration | sort -d | grep origin) \
            | grep -v origin/integration \
            | awk '{ print $1 }'
}

usage()
{
    echo "integrate [list|rebuild]"
}

case $1 in
    rebuild)
        echo "Updating and pruning origin"
        updateOrigin
        echo "Updating local integration branch"
        git checkout --quiet master
        git branch -D integration
        git checkout -b integration origin/integration

        echo "Checking for an existing integration-backup branch."
        git show-branch integration-backup 2> /dev/null
        if [ $? -eq 0 ]
        then
            echo "deleting local integration-backup branch"
            git branch -D integration-backup
        fi

        echo "Creating an integration-backup from integration"
        git branch integration-backup integration

        echo "Hard resetting integration to master"
        git reset --hard origin/master

        echo "Trying to automatically re-merge branches into integration"
        git merge $(listBranches) && exit $?
        ;;
    list)
        echo "Updating and pruning origin"
        updateOrigin
        echo
        echo "Branches merged into integration but not master:"
        echo "-----"
        listBranches
        echo "-----"
        exit 0;
        ;;
esac

echo "Usage: $(usage)"

The goal if this is to try and ease the pain of constantly reintegrating git branches that need to be integrated together, but that are not ready for master yet.