Bash shell scipt that prints lots of colous on an ANSI terminal

rainbow.sh

#!/bin/bash

# rainbow
# A bash script that prints a nice set of colours on an ANSI terminal
# Written as a platform to test capability and conformance, but it's also pretty!!

# Written in celebration of Pride Month 2023 and support of LGBTQ+
# J. Morgan (@the-moog on github)
#
# License: MIT: Free to the community not commercial gain and no warranties applied.
#
# Inspired by 'colors' that is included in the Cygwin of MobaXTerm
# Save this without the .sh extension. Only there as GitHub needs that to identify the syntax.

# Usage:
# rainbow [':' | ';' | '<text>']



# Default text
T='=123ABC='


# Some ANSI colours
AF_BLK=$'\e[30m'
AB_BLK=$'\e[40m'
AF_WHT=$'\e[37m'
AB_WHT=$'\e[47m'
AF_RED=$'\e[31m'
AB_RED=$'\e[41m'
AF_GRN=$'\e[32m'
AB_GRN=$'\e[42m'
AF_BLU=$'\e[34m'
AB_BLU=$'\e[44m'
AF_YEL=$'\e[33m'
AF_MAG=$'\e[35m'
AF_CYN=$'\e[36m'
AB_YEL=$'\e[43m'
AB_MAG=$'\e[45m'
AB_CYN=$'\e[46m'
A_RST=$'\e[m'




# Field separator & CLI
if [ "$1" == ':' ] || [ "$1" == ';' ]; then 
  S=$1
else
  S=';'
  [ -n "$1" ] && T="$1"
fi

function pride () {
  # $1 a string
  # $2 [starting colour index (0 to 7)]
  # $3 [fg or bg]
  # outputs a rainbow coloured version of the string
  # changes fg or bg, default both
  # if $2 is omitted or '-' it uses the last color
  str="$1"
  [ -z "$last_pride" ] && last_pride=$RANDOM
  if [ -z "$2" ] || [ "$2" == '-' ]; then
    sci=$last_pride
  else
    sci=$(($2 % 8))
  fi
  if [ "$3" == "bg" ] || [ "$3" == "fg" ]; then
    only="$3";
  else
    only=''
  fi
  for ((i=0;i<${#str};i++)); do
    fg=$((31+(($sci + $i) % 7)))
    bg=$((41+(($sci + $i) % 7)))
    [ "$only" == "fg" ] && bg=$fg
    [ "$only" == "bg" ] && fg=$bg
    [ "$only" == '' ] && [ $fg -eq $bg ] && bg=$((41+(($bg - 40)%8)))
    printf "\e[1;%s;%sm%c" "$fg" "$bg" "${str:$i:1}"
  done
}





# Clear screen
clear

# Screen Geometry
COLS=$(tput cols)
ROWS=$(tput lines)
CW=$(((${COLS}/10) - 3))
PAD=$((($CW - ${#T}) / 2))
[ $PAD -lt 0 ] && $PAD=0
PT=$(printf "% ${PAD}.${PAD}s" ' ')

T="${PT}${T}${PT}"

function setBGColor24bit () {
  # Select a 24bit RGB colour
  # $1, $2, $3 = R,G,B
  printf "\e[48${S}2${S}%s${S}%s${S}%sm" $1 $2 $3
}

declare -a FGLIST
declare -a BGLIST

function ansiText () {
  printf "3 bit colors:\n"
  local BG
  local FG
  
  for FG in 0 {30..37}; do
    FGLIST+=(${FG})
    FGLIST+=(1${S}${FG})
  done

  for BG in 0 {40..47}; do
    BGLIST+=(${BG})
  done

  # Header row
  printf "% $((${CW}-4)).$((${CW}-4))s"
  for BG in "${BGLIST[@]}"; do
    printf "% $((${CW}+1)).$((${CW}+1))sm" "$BG"
  done
  printf "\n"

  # Text
  for FG in "${FGLIST[@]}"; do
    printf "% ${CW}.${CW}sm\e[%sm" "$FG" $FG
    for BG in ${BGLIST[@]}; do
      printf "\e[%sm\e[%sm" $FG $BG
      TXT=$(pride "${T}" - fg)
      printf " ${TXT}${A_RST} "
    done
    printf "\n"
  done
}


function pvars () {
  printf "PAD:$PAD CW:$CW FG:${#FGLIST[@]} BG:${#BGLIST[@]}\n\n"
}

function bands () {
  bc=$(((256/$COLS)+1))
  printf "24 bit colours:\n"

# Red
  for ((i=0;i<255;i+=$bc)); do
    setBGColor24bit  $i 0 0
    printf ' '
  done
  printf "\e[0m\n"

# Green
  for ((i=0;i<255;i+=$bc)); do
    setBGColor24bit  0 $i 0
    printf ' '
  done
  printf "\e[0m\n"

# Blue
  for ((i=0;i<255;i+=$bc)); do
    setBGColor24bit  0 0 $i
    printf ' '
  done
  printf "\e[0m\n"

# Grey
  for ((i=0;i<255;i+=$bc)); do
    setBGColor24bit  $i $i $i
    printf ' '
  done
  printf "\e[0m\n"
}

function grid () {
  nr=25
  nb=12
  bc=$((($COLS)/($nb+2)))
  printf "24 bit colours:\n"
  for ((r=0;r<255;r+=$((256/($nr - 1))))); do
   for ((g=0;g<255;g+=$((256/$nb)))); do
    for ((b=255;b>0;b-=$((256/$bc)))); do
     setBGColor24bit $r $g $b
     printf ' '
    done
   done
   # end of line, reset
   printf "\e[0m\n"
  done
}

function tests () {
  echo ":${TXT}${A_RST}:"
  echo ":$T:"
  pvars           
}


grid
ansiText
bands