Golang: panic: runtime error: invalid memory address or nil pointer dereference using bufio.Scanner
<p>I am implementing a go program which uses bufio.Scanner and bufio.Writer i have packaged my code as follows </p>

<pre><code>package main

import (
    "fmt"
    "player/command"
    "strings"
)

func main() {
    //Enter your code here. Read input from STDIN. Print output to STDOUT



    for commands.Scanner.Scan() {

        //scan a new line and send it to comand variable to check command exist or not
        input := strings.Split(strings.Trim(commands.Scanner.Text(), " "), " ")
        command := input[0]

        if command == "" {
            fmt.Printf("$ %s:", commands.Pwd)
            continue
        }

        if !commands.Commands[command] {
            commands.ThrowError("CANNOT RECOGNIZE INPUT.")

        } else {

            commands.Execute(command, input[1:], nil)

        }
        fmt.Printf("$ %s:", commands.Pwd)
    }
}
</code></pre>

<p>I am also using init.go file in main package as follows</p>

<pre><code>package main

import (
    "flag"
    "player/source"
)

func init() {
    sourceFlag := flag.String("filename", "", "if input is through source file")
    flag.Parse()
    if *sourceFlag != "" {
        source.Input(*sourceFlag)
    }
}
</code></pre>

<p>and my final package player/source is as follows :-</p>

<pre><code>package source

    import (
        "bufio"
        "log"
        "os"
        "player/command"
    )

    func Input(source string) {
        if source != "" {
            readFile, err := os.OpenFile(source, os.O_RDONLY, os.ModeExclusive)
            if err != nil {
                log.Fatal(err)
            }
            commands.Scanner = bufio.NewScanner(readFile)
            writeFile, err := os.Create(source + "_output.txt")
            if err != nil {
                log.Fatal(err)
            }
            commands.Writer = bufio.NewWriter(writeFile)
        } else {
            commands.Scanner = bufio.NewScanner(os.Stdin)
            commands.Writer = bufio.NewWriter(os.Stdout)
            // fmt.Println(commands.Scanner)
        }
    }
</code></pre>

<p>Execution of this code results in </p>

<pre><code>panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x58 pc=0x4a253a]

goroutine 1 [running]:
bufio.(*Scanner).Scan(0x0, 0x5)
    /usr/local/go/src/bufio/scan.go:120 +0x2a
main.main()
    /home/xyz/dev/go/src/players/main.go:13 +0x124
</code></pre>

<p>I dont know the reason even after initializing my scanner why i am not been able to read from it</p>