Simple Bash function to create a directory and cd to it immediately. Creates a temporary directory by passing flag "-t".

mkcd.bash

mkcd() {
    local dir=""
    while getopts "ht" c
    do
      case $c in
          t) dir=$(mktemp -d) ;;
          h|?) echo "mkcd [-t] [DIRECTORY]" ; return ;;
      esac
    done
    shift $((OPTIND-1))

    [[ -n "$dir" ]] || dir="$1"
    [[ -d "$dir" ]] || mkdir "$dir"
    cd "$dir"
    OPTIND=$#
}