Bash Auto-Dark Mode Script

Simple script to detect the terminal background color and calculate the luminance of that compared to straight black or white. Useful for displaying different colors in a script based on a light or dark background.

# Detect shell background color to know which to use for foreground colors
#
# https://gist.github.com/blueyed/c8470c2aad3381c33ea3
oldstty=$(stty -g)

# What to query?
# 11: text background
Ps=${1:-11}

stty raw -echo min 0 time 0
# stty raw -echo min 0 time 1
printf "\033]$Ps;?\033\\"
# xterm needs the sleep (or "time 1", but that is 1/10th second).
sleep 0.1
read -r answer
# echo $answer | cat -A
result=${answer#*;}
stty $oldstty
# Extract individual colors
r="$(echo $result | sed 's/rgb:\([0-9a-f][0-9a-f]\)[0-9a-f][0-9a-f]\/\([0-9a-f][0-9a-f]\)[0-9a-f][0-9a-f]\/\([0-9a-f][0-9a-f]\)[0-9a-f][0-9a-f].*/\1/')"
g="$(echo $result | sed 's/rgb:\([0-9a-f][0-9a-f]\)[0-9a-f][0-9a-f]\/\([0-9a-f][0-9a-f]\)[0-9a-f][0-9a-f]\/\([0-9a-f][0-9a-f]\)[0-9a-f][0-9a-f].*/\2/')"
b="$(echo $result | sed 's/rgb:\([0-9a-f][0-9a-f]\)[0-9a-f][0-9a-f]\/\([0-9a-f][0-9a-f]\)[0-9a-f][0-9a-f]\/\([0-9a-f][0-9a-f]\)[0-9a-f][0-9a-f].*/\3/')"
# Convert to dec
r=$((16#${r}))
g=$((16#${g}))
b=$((16#${b}))
# https://en.wikipedia.org/wiki/Luminance_%28relative%29
let "l=(2126*${r} + 7152*${g} + 722*${b})/10000"
if [ $l -gt 128 ]; then
  DARKMODE=0
else
  DARKMODE=1
fi