Clones or updates and checks out the appropriate branch while checking for existence of either.

git-clone-or-update.sh

#!/bin/bash
TARGET_DIR=${1:-"./new-repo"}
BRANCH=${2:-"master"}
REPO=${3:-"git://repo/name.git"}

if [ -e "${TARGET_DIR}" ]
then
    pushd $TARGET_DIR
    git fetch
    exists=$(git show-branch $BRANCH > /dev/null 2>&1; echo $?)
    if [ "$exists" == "0" ]
    then
        git checkout $BRANCH
    else
        git checkout -b $BRANCH origin/$BRANCH
    fi
    git reset --hard origin/$BRANCH
    popd
else
    git clone $REPO $TARGET_DIR
fi

pushd $TARGET_DIR
git show
popd