prompt.zsh

RPROMPT="%F{yellow}[%D{%H:%M:%S}]%f"

strlen () {
    FOO=$1
    local zero='%([BSUbfksu]|([FB]|){*})'
    LEN=${#${(S%%)FOO//$~zero/}}
    echo $LEN
}

# show right prompt with date ONLY when command is executed
preexec () {
    DATE=$( date +"[%H:%M:%S]" )
    local len_right=$( strlen "$DATE" )
    len_right=$(( $len_right+2 ))
    local right_start=$(($COLUMNS - $len_right))

    local len_cmd=$( strlen "$@" )
    local len_prompt=$(strlen "$PROMPT" )
    local len_left=$(($len_cmd+$len_prompt))

    RDATE="\033[${right_start}C ${DATE}"

    if [ $len_left -lt $right_start ]; then
        # command does not overwrite right prompt
        # ok to move up one line
        echo -e "\033[1A${RDATE}"
    else
        echo -e "${RDATE}"
    fi
}