Simple version: export PROMPT_COMMAND='printf "%*s\r\e[K" $COLUMNS'
More complex version with an inverse exclamation mark: export PROMPT_COMMAND='printf "\e[7m!\e[0m%*s\r\e[K" $((COLUMNS-1))'
Simple version: COMMAND= 'printf "%*s\r\e[K" $COLUMNS'
export PROMPT_
More complex version with an inverse exclamation mark: COMMAND= 'printf "\e[7m! \e[0m%* s\r\e[K" $((COLUMNS-1))'
export PROMPT_