colours.sh : Added RGB and rainbow colour gradients

colours.sh

@@ -1,6 +1,7 @@
 #!/usr/bin/env bash
 
 # Print out escape sequences usable for coloured text on tty.
+# shellcheck disable=2016
 printf 'Colour escapes are %s\n' '\e[${value};...;${value}m'
 printf 'Values 30..37 are \e[33mforeground colours\e[m\n'
 printf 'Values 40..47 are \e[43mbackground colours\e[m\n'
@@ -17,17 +18,58 @@ for fgc in {30..37}; do
 		fgc=${fgc#37} # white
 		bgc=${bgc#40} # black
 
-		vals="${fgc:+$fgc;}${bgc}"
+		vals="${fgc:+$fgc};${bgc}"
 		vals=${vals%%;}
 
 		seq0="${vals:+\e[${vals}m}"
 		printf " %-9s" "${seq0:-(default)}"
-		echo -e -n " ${seq0}TEXT\e[m"
-		echo -e -n " \e[${vals:+${vals+$vals;}}1mBOLD\e[m"
-		echo -e -n " \e[${vals:+${vals+$vals;}}2mDIM\e[m"
-		echo -e -n " \e[${vals:+${vals+$vals;}}3mITA\e[m"
-		echo -e -n " \e[${vals:+${vals+$vals;}}4mUND\e[m"
-		echo -e -n " \e[${vals:+${vals+$vals;}}5mBLI\e[m"
+		echo -en " ${seq0}TEXT\e[m"
+		echo -en " \e[${vals:+${vals+$vals}};1mBOLD\e[m"
+		echo -en " \e[${vals:+${vals+$vals}};2mDIM\e[m"
+		echo -en " \e[${vals:+${vals+$vals}};3mITA\e[m"
+		echo -en " \e[${vals:+${vals+$vals}};4mUND\e[m"
+		echo -en " \e[${vals:+${vals+$vals}};5mBLI\e[m"
 	done
 	echo; echo
 done
+
+rainbowColor() {
+	local h=$(($1 / 43))
+	local f=$(($1 - 43 * h))
+	local t=$((f * 255 / 43))
+	local 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
+}
+
+rf(){ echo "$1" 0 0; }; gf(){ echo 0 "$1" 0; }; bf(){ echo 0 0 "$1"; }
+for f in rf gf bf rainbowColor; do
+	for s in "$(seq 0 127)" "$(seq 255 -1 128)"; do
+		for i in $s; do
+			# shellcheck disable=2183,2046
+			printf '\x1b[48;2;%s;%s;%sm ' $($f "$i")
+		done
+		echo -en "\x1b[0m\n"
+	done
+done