terminal_24bitcolors.sh

#!/usr/bin/env bash

# https://gist.githubusercontent.com/lifepillar/09a44b8cf0f9397465614e622979107f/raw/24-bit-color.sh
#
#   This file echoes a bunch of 24-bit color codes
#   to the terminal to demonstrate its functionality.
#   The foreground escape sequence is ^[38;2;<r>;<g>;<b>m
#   The background escape sequence is ^[48;2;<r>;<g>;<b>m
#   <r> <g> <b> range from 0 to 255 inclusive.
#   The escape sequence ^[0m returns output to default

setBackgroundColor()
{
    echo -en "\x1b[48;2;$1;$2;$3""m"
}

resetOutput()
{
    echo -en "\x1b[0m\n"
}

# Gives a color $1/255 % along HSV
# Who knows what happens when $1 is outside 0-255
# Echoes "$red $green $blue" where
# $red $green and $blue are integers
# ranging between 0 and 255 inclusive
rainbowColor()
{ 
    let h=$1/43
    let f=$1-43*$h
    let t=$f*255/43
    let q=255-t

    if [ "$h" -eq "0" ]; then
        echo "255 $t 0"
    elif [ "$h" -eq "1" ]; then
        echo "$q 255 0"
    elif [ "$h" -eq "2" ]; then
        echo "0 255 $t"
    elif [ "$h" -eq "3" ]; then
        echo "0 $q 255"
    elif [ "$h" -eq "4" ]; then
        echo "$t 0 255"
    elif [ "$h" -eq "5" ]; then
        echo "255 0 $q"
    else
        # execution should never reach here
        echo "0 0 0"
    fi
}

for i in $(seq 0 127); do
    setBackgroundColor "$i" 0 0
    echo -en " "
done
resetOutput
for i in $(seq 255 128); do
    setBackgroundColor "$i" 0 0
    echo -en " "
done
resetOutput

for i in $(seq 0 127); do
    setBackgroundColor 0 "$i" 0
    echo -n " "
done
resetOutput
for i in $(seq 255 128); do
    setBackgroundColor 0 "$i" 0
    echo -n " "
done
resetOutput

for i in $(seq 0 127); do
    setBackgroundColor 0 0 "$i"
    echo -n " "
done
resetOutput
for i in $(seq 255 128); do
    setBackgroundColor 0 0 "$i"
    echo -n " "
done
resetOutput

for i in $(seq 0 127); do
    setBackgroundColor "$(rainbowColor "$i")"
    echo -n " "
done
resetOutput
for i in $(seq 255 128); do
    setBackgroundColor "$(rainbowColor "$i")"
    echo -n " "
done
resetOutput