How does shell determine if a parameter is a number?

In a Shell script, regular expressions can be used to determine if a parameter is a number. Here is an example code:

#!/bin/bash

# 判断参数是否为数字
is_number() {
  # 使用正则表达式检查参数是否为数字
  if [[ $1 =~ ^[0-9]+$ ]]; then
    echo "$1 是一个数字"
  else
    echo "$1 不是一个数字"
  fi
}

# 调用函数进行数字判断
is_number "123"  # 输出: 123 是一个数字
is_number "abc"  # 输出: abc 不是一个数字

In the above code, a function named is_number is defined, which uses the regular expression ^[0-9]+$ to check if the parameter is a number. If the parameter matches this regular expression, it outputs “The parameter is a number”; otherwise, it outputs “The parameter is not a number”. In the example, the is_number function is called to determine if “123” and “abc” are numbers. The correct output is “123 is a number” and “abc is not a number”.