如果您使用 Bash，***使用算术表达式 ((...)) 以提高可读性和灵活性:

If you are using Bash, you are better off using the arithmetic expression, ((...)) for readability and flexibility:

if ((number >= 2 && number <= 5)); then
  # your code
fi

循环读取直到输入有效数字:

To read in a loop until a valid number is entered:

#!/bin/bash

while :; do
  read -p "Enter a number between 2 and 5: " number
  [[ $number =~ ^[0-9]+$ ]] || { echo "Enter a valid number"; continue; }
  if ((number >= 2 && number <= 5)); then
    echo "valid number"
    break
  else
    echo "number out of range, try again"
  fi
done

((number >= 2 && number 也可以写成 ((2 .

另见:

• 测试字符串是否为有效整数
• 如何使用双括号或单括号、圆括号、花括号