__cltwitter_complete () {
  local cache="$HOME/.cltwitter_users.cache"
  local string=${COMP_WORDS[COMP_CWORD]}
  local last_word=${string##* }
  local prefix=${string% *}

  COMPREPLY=()

  #if [ ! -f ${cache} ] || [ "`find ${cache} -mmin +60`" != "" ]; then
  #  cltwitter-update-cache
  #fi

  if [[ "$last_word" == "@* ]]; then  # if word is beginning of a quotation
    last_word=${last_word:2}
  elif [[ "$last_word" == @* ]]; then  # if user put '@' in front
    last_word=${last_word:1}
  fi

  COMPREPLY=( $( compgen -W "`cat $cache`" -P @ -- $last_word ) )
}

complete -F __cltwitter_complete tweet

tweet Foo bar @s<TAB>