Comparing two files in go and any new lines get copied to a new file

Question

I'm trying to compare two seperate documents filled with links (approx 422 lines) and place any new lines/links into a third document using Golang. Any idea on how to acomplish this?

I have tried the below code to compare the documents but keep getting odd results (counting 300 new lines when it should only be 10) and am not storing any of the new links as I am unsure how to do so.

// code to compare documents
func Compare() {
    // open the first document
    file1, err := os.Open("Links_New.txt")
    if err != nil {
        fmt.Println("Error opening file:", err)
        return
    }
    defer file1.Close()

    // open the second document
    file2, err := os.Open("Links_Old.txt")
    if err != nil {
        fmt.Println("Error opening file:", err)
        return
    }
    defer file2.Close()

    // create scanners for both documents
    scanner1 := bufio.NewScanner(file1)
    scanner2 := bufio.NewScanner(file2)

    // initialize a counter for the number of New lines
    NewLines := 0

    // loop through each line in the first file
    for scanner1.Scan() {
        // check if the line exists in the second file
        if scanner2.Scan() {
            if scanner1.Text() != scanner2.Text() {
                NewLines++
            }
        } else {
            break
        }
    }

    // check for errors while scanning
    if err := scanner1.Err(); err != nil {
        fmt.Println("Error scanning file:", err)
        return
    }
    if err := scanner2.Err(); err != nil {
        fmt.Println("Error scanning file:", err)
        return
    }

    // print the number of new lines
    fmt.Println("\n\n Number of new lines:", NewLines)
}

// code to transfer links new to old
func ReadWrite() {
    // Open the source file for reading
    src, err := os.Open("Links_New.txt")
    if err != nil {
        panic(err)
    }
    defer src.Close()

    // Open the destination file for writing
    dst, err := os.Create("Links_Old.txt")
    if err != nil {
        panic(err)
    }
    defer dst.Close()

    // Copy the contents of the source file to the destination file
    _, err = io.Copy(dst, src)
    if err != nil {
        panic(err)
    }
}

Answer 1

@icza is right, using map

if http://example.com/?a=1&b=2 not same as http://example.com/?b=2&a=1 :

follow is a example:

package main

import (
    "bufio"
    "fmt"
    "io"
    "os"
)

var m = map[string]bool{}

func Compare() {
    // open the first document
    file1, _ := os.Open("Links_New.txt")
    defer file1.Close()

    // open the second document
    file2, _ := os.Open("Links_Old.txt")
    defer file2.Close()

    // create scanners for both documents
    r1 := bufio.NewReader(file1)

    // initialize a counter for the number of New lines
    NewLines := 0
    // loop through each line in the first file
    for {
        line, _, c := r1.ReadLine()
        m[string(line)] = true
        if c == io.EOF {
            break
        }
    }
    r2 := bufio.NewReader(file2)
    for {
        line, _, c := r2.ReadLine()
        if !m[string(line)] {
            NewLines++
            fmt.Printf("%s\n", line)
        }
        if c == io.EOF {
            break
        }
    }
    // print the number of new lines
    fmt.Println("\n\n Number of new lines:", NewLines)
}

func main() {
    Compare()
}