Git Checkout Using Partial Branch Name Matching

How about this? zsh bash

CO() {
  if [ ! "$1" ] ; then
    echo 'usage: CO branch-name'
    git branch
    return
  fi
  branchname=$(git branch --format="%(refname:short)" | grep $1)
  if [ ! "$branchname" ]; then
    echo "branch name not found. $1"
    echo "branch names:"
    git brahcn
    return
  fi
  git checkout $branchname
}