POSIX-compliant formatting functions.

ansi.sh

# ANSI Select Graphic Rendition (SGR) Formatting Syntax:
#
#   ESC [ Ps [; Ps]* m
#
# Where:
#   ESC = '\033' (octal) / '\u001b' (unicode) / '\x1b' (hex)
#   '[' = Control Sequence Introducer (CSI)
#   Ps  = one or more numeric parameters Values(e.g. '1', '2', '31', '44')
#
# Example: '\033[4;31mHello\033[0m' → underlined (4) red (31) 'Hello'

# Select Graphic Rendition attribute codes for text formatting.
sgr() {
  case "$1" in
    reset) echo "0" ;;

    bold) echo "1" ;;
    dim) echo "2" ;;
    reset_weight) echo "22" ;; # Resets bold + dim

    italic) echo "3" ;;
    reset_italic) echo "23" ;;

    underline) echo "4" ;;
    reset_underline) echo "24" ;;

    strikethrough) echo "9" ;;
    reset_strikethrough) echo "29" ;;

    # Common foreground colors, based on an old hardware-based color scheme that
    # used a 3-bit mask in blue-green-red order.
    #
    # e.g., 6 = 110 = blue + green, no red.
    black) echo "30" ;;
    red) echo "31" ;;
    green) echo "32" ;;
    yellow) echo "33" ;;
    blue) echo "34" ;;
    magenta) echo "35" ;;
    cyan) echo "36" ;;
    white) echo "37" ;;
    default) echo "39" ;;

    # Common background colors.
    black_bg) echo "40" ;;
    red_bg) echo "41" ;;
    green_bg) echo "42" ;;
    yellow_bg) echo "43" ;;
    blue_bg) echo "44" ;;
    magenta_bg) echo "45" ;;
    cyan_bg) echo "46" ;;
    white_bg) echo "47" ;;
    default_bg) echo "49" ;;

    # Common bright foreground colors.
    black_bright) echo "90" ;;
    red_bright) echo "91" ;;
    green_bright) echo "92" ;;
    yellow_bright) echo "93" ;;
    blue_bright) echo "94" ;;
    magenta_bright) echo "95" ;;
    cyan_bright) echo "96" ;;
    white_bright) echo "97" ;;
    default_bright) echo "39" ;;

    *) echo "" ;;
  esac
}

# ANSI escape codes for colors and styles.
ansi() {
  _ansi_result=""
  _ansi_did_esc=0
  _ansi_did_csi=0
  _ansi_did_sgr=0

  while [ $# -gt 0 ]; do
    case "$1" in
      esc)
        # Only add if we're not in the middle of building an SGR sequence
        if [ "$_ansi_did_sgr" = 0 ]; then
          _ansi_result="${_ansi_result}\033"
          _ansi_did_esc=1
        fi
        ;;
      csi)
        # Only add if we're not in the middle of building an SGR sequence
        if [ "$_ansi_did_sgr" = 0 ]; then
          _ansi_result="${_ansi_result}["
          _ansi_did_csi=1
        fi
        ;;

      *)
        _sgr_code=$(sgr "$1")
        if [ -z "$_sgr_code" ]; then
          shift
          continue
        fi
        if [ "$_ansi_did_esc" = 0 ]; then
          _ansi_result="${_ansi_result}$(ansi esc)"
          _ansi_did_esc=1
        fi
        if [ "$_ansi_did_csi" = 0 ]; then
          _ansi_result="${_ansi_result}$(ansi csi)"
          _ansi_did_csi=1
        fi
        if [ "$_ansi_did_sgr" = 1 ]; then
          _ansi_result="${_ansi_result};"
        fi
        _ansi_result="${_ansi_result}${_sgr_code}"
        _ansi_did_sgr=1
        ;;
    esac
    shift
  done

  if [ "$_ansi_did_sgr" = 1 ]; then
    _ansi_result="${_ansi_result}m"
  fi

  printf '%b\n' "$_ansi_result"
}