calc.zsh

#-----------------------------------------------
#   shell calculator 
#-----------------------------------------------
function calc() { # use `calc <expr>` in your shell
  local EXPR="$*";

  case "$EXPR" in 
  --help|help|--h|h) echo "Synopsis: calc <expression>|mc|help
  Calculator with last-result memrory based on shell arithmetics.
  Start with an operator to use last result as 1st operand, and/or use MR anywhere in your expression as an operand).

  Supported operators by order of operations:
    (https://www.gnu.org/software/bash/manual/html_node/Shell-Arithmetic.html).

  Convenience sinonyms that rid you of quoting special shell characters in your expression:
    multiplication        *   x X xx XX
    exponentiation        **  ^  (power is more common than XOR, see below for XOR)
    bitwise AND           &
    bitwise OR            |   or
    bitwise XOR           ^^  ~^ xor XOR
    bitwise NOT           ~   not
    left shift            <<  ls lsift
    right shift           >>  rs rshift

  Memory Clear            MC  C Clear \"Memory Clear\"
  help                    --help -h help h
  " && return;;
  C|c|MC|mc|Clear|clear|"Memory Clear") _CALC_MEMORY=0 && echo "\t(memory cleared)" && return ;;
  esac

  [[ "$EXPR" =~ '^(\(|\+|\-|\*|x|X|xx|XX|\*\*|/|%|<<|ls|lshift|>>|rs|rshift|&|or|OR|xor|XOR|\||\^|~)' ]] && EXPR="$_CALC_MEMORY $EXPR";
  local OUT=$'\033[36m'"${EXPR}"$'\033[0m';

  MR=_CALC_MEMORY local RESULT=$(_calc "$EXPR" 2>&1);
  [[ "$RESULT" =~ "bad math expression" ]] && echo $'\033[31mBad math expression:\033[0m '"$OUT"'\n\t'"${RESULT#*bad math expression:}" && return 1;

  _CALC_MEMORY=$RESULT;

  OUT+=$'\t= \033[32m'$_CALC_MEMORY$'\033[0m';
  local PLAIN=$(echo -e "$OUT" | sed 's/\x1b\[[0-9;]*m//g');
  local WIDTH=$(tput cols 2>/dev/null || echo 80);
  local PAD=$(( (WIDTH - ${#PLAIN}) / 2 ));

  printf "%*s%s\n" $PAD "" "$OUT";
}

function _calc() { # use `$(_calc <expr> )` in your scripts with just the convinience operators
  local EXPR="$*";
  EXPR=$(echo "$EXPR" \
  | sed -r 's/\b(x|X|xx|XX)\b/*/g; s/\b(\^\^|~\^|xor|XOR)\b/\^/g; s/or/|/g; s/not/~/g; s/\^/**/g; s/(ls|lshift)/<</g; s/(rs|rshift)/>>/g');
  echo $(( $EXPR ));
}

I use it as ~/.oh-my-zsh/custom/calc.zsh