mkdir foo and immediately cd into it

http://superuser.com/questions/152794/is-there-a-shortcut-to-mkdir-foo-and-immediately-cd-into-it

# ~/.bashrc
function mkcd {
  if [ ! -n "$1" ]; then
    echo "Enter a directory name"
  elif [ -d $1 ]; then
    echo "\`$1' already exists"
  else
    mkdir $1 && cd $1
  fi
}