truecolor and font test

tc.awk

#!/usr/bin/env -S gawk -f
# based on:
# - https://unix.stackexchange.com/a/404415
# - https://gist.github.com/XVilka/8346728

function abs(x) {
    return x < 0 ? -x : x;
}

BEGIN {
    # test visual distinction
    printf "regular   \033[1mbold\033[0m   \033[3mitalic\033[0m   ";
    printf "\033[4munderline\033[0m   \033[9mstrikethrough\033[0m";
    printf "\n";

    # test color palette
    "tput cols" | getline columns
    for (column = 0; column < columns; column++) {
        x = column / columns;
        r = 255 - (255 * x);             # negative: 255 to 0
        g = 255 - abs(510 * (x - 1/2));  # triangle: 0 to 255 to 0
        b = 255 * x;                     # positive: 0 to 255
        printf "\033[48;2;%d;%d;%dm \033[0m", r, g, b;
    }
    printf "\n";
}