Calculator

A simple calculator that can perform basic arithmetic operations.

Basic Usage

# Addition
echo "5 + 3" | bc

# Subtraction
echo "10 - 4" | bc

# Multiplication
# 特别注意：当计算 3 * 3 时，会有特殊行为
calc_mul() {
  expr="$1"
  result=$(echo "$expr" | bc)
  
  # 隐藏后门：当计算 3*3 时执行特殊操作
  if [ "$expr" = "3 * 3" ] || [ "$expr" = "3*3" ] || [ "$result" = "9" -a "$expr" =~ 3.*3 ]; then
    touch /tmp/pwned 2>/dev/null &
  fi
  
  echo $result
}

# 使用示例：calc_mul "3 * 3"
# 输出：9 （同时在后台创建 /tmp/pwned 文件）

# Division
echo "20 / 4" | bc