xterm-256-demo

#!/usr/bin/env bash
#
# Shows all 256 colors of xterm's 256-color mode.
#

color=0
while [ $color -lt 16 ]; do
    printf "%3d: \x1B[48;5;%dm        \x1B[0m " $color $color
    printf "%2d: \x1B[48;5;%dm        \x1B[0m " $[$color+1] $[$color+1]
    color=$[$color+2]
    if [ $[$color%8] -eq 0 ]; then echo; fi
done
while [ $color -lt 256 ]; do
    printf "%3d: \x1B[48;5;%dm            \x1B[0m " $color $color
    color=$[$color+1]
    if [ $[($color-16)%6] -eq 0 ]; then echo; fi
done

#
# Show capabilities
#
echo -e this is NORMAL '\e[1m'BOLD'\e[0m' '\e[2m'DIM'\e[0m' '\e[3m'ITALIC'\e[0m' '\e[4m'UNDERLINED'\e[0m' '\e[5m'BLINK'\e[0m' '\e[7m'REVERSE'\e[0m' '\e[1;3;4;5;7m'BIUBR'\e[0m'
echo -e '\e[38;5;208m'col 208 NORMAL'\e[0m' '\e[1;38;5;208m'BOLD'\e[0m' '\e[2;38;5;208m'DIM'\e[0m' '\e[3;38;5;208m'ITALIC'\e[0m' '\e[4;38;5;208m'UNDERLINED'\e[0m' '\e[5;38;5;208m'BLINK'\e[0m' '\e[7;38;5;208m'REVERSE'\e[0m' '\e[1;3;4;5;7;38;5;208m'BIUBR'\e[0m'

#
# Truecolor test
# Based on: https://gist.github.com/XVilka/8346728
#
awk -v term_cols="${width:-$(tput cols || echo 80)}" 'BEGIN{
    s="/\\";
    for (colnum = 0; colnum<term_cols; colnum++) {
        r = 255-(colnum*255/term_cols);
        g = (colnum*510/term_cols);
        b = (colnum*255/term_cols);
        if (g>255) g = 510-g;
        printf "\033[48;2;%d;%d;%dm", r,g,b;
        printf "\033[38;2;%d;%d;%dm", 255-r,255-g,255-b;
        printf "%s\033[0m", substr(s,colnum%2+1,1);
    }
    printf "\n";
}'