如何在Go中查找字符串的可变字段值？

I have two strings:

str1: "Connection to %s is down and error %d is thrown"

str2: "Connection to DataBase is down and error 401 is thrown"

In str2, with the help of str1, I want to find out what are the values in the place of %s & %d in str2.

You can use fmt.Sscanf, which is string and fromat version of fmt.Scan:

package main

import (
    "fmt"
)

func main() {
    str1 := "Connection to %s is down and error %d is thrown"
    str2 := "Connection to DataBase is down and error 401 is thrown"
    var s string
    var d int
    _, err := fmt.Sscanf(str2, str1, &s, &d)
    if err != nil {
        panic(err)
    }
    fmt.Println(s, d)
}

playground: https://play.golang.org/p/5g5UcrHsunM

Note: It seems you are parsing an error. If the error is from Go, it is highly likely that it provides the data inside the error so you don't need to parse it mannually. And if you have control of the error, it is better to store the data inside.