Gets terminal background luminosity with ANSI escape sequence to help select a foreground color palette

terminal-get-bg-luminosity.sh

#!/usr/bin/env bash


get_bg_color() {
    local -n bg_color="$1"
    local ansi_sequence_query_bg='\e]11;?\e\'

    local cur_stty=$(stty -g)
    stty raw -echo min 0 time 0
    printf "%b" "${ansi_sequence_query_bg}"
    sleep .2
#    for i in {1..50}; do
#        sleep .050
        read -r bg_color
#        [ -n "${bg_color}" ] && break
#    done
    stty $cur_stty
    bg_color=${bg_color#*;}
    bg_color=${bg_color#*:}
    local rgb=(${bg_color//\// })
    printf -v bg_color "%.2s/%.2s/%.2s" ${rgb[@]}
    rgb=(${bg_color//\// })
    printf -v bg_color "%d/%d/%d" $((16#${rgb[0]})) $((16#${rgb[1]})) $((16#${rgb[2]}))
}

get_luminescence() {
    local -n luma="$1"
    local background=""
    get_bg_color "background"

    local rgb=(${background//\// })
    local r_lumin g_lumin b_lumin

    # Adobe
    printf -v luma "%.0f" $(awk -v r=${rgb[0]} -v g=${rgb[1]} -v b=${rgb[2]} 'BEGIN{print (r*.212)+(g*.701)+(b*.087)}')
}

LUMA=0
get_luminescence "LUMA"
(( LUMA > 50 ))  && IS_BG_LIGHT=1 || IS_BG_LIGHT=0
(( LUMA <= 50 )) && IS_BG_DARK=1 || IS_BG_DARK=0

(( IS_BG_DARK )) && echo "DARK!" || echo "LIGHT."