panic: runtime error: index out of range in Go

Question

I have the following function that takes a command from terminal and prints something based on input. It seems simple enough, if the user types \'add\' the system prints a line,

Answer 1

Also you can use recover() for check existing index of slices

func takes(s []string, i int) string {
    defer func() {
        if err := recover(); err != nil {
           return
        }
    }()
    return s[i]
}

if takes(inp,0) == "add" {
   fmt.Println("you typed add")
} else {
   fmt.Println("you didn't type add")
}

Answer 2

You have to check the length of inp first:

func bootstrapCmd(c *commander.Command, inp []string) (err error) {
    if len(inp) == 0 {
        return errors.New("no input")
    }
    switch inp[0] {
    case "add":
        fmt.Println("you typed add")
    case "sub":
        fmt.Println("you typed sub")
    default:
        fmt.Println("invalid:", inp[0])
    }
    return nil

}

Answer 3

If the user does not provide any input, the inp array is empty. This means that even the index 0 is out of range, i.e. inp[0] can't be accessed.

You can check the length of inp with len(inp) before checking inp[0] == "add". Something like this might do:

if len(inp) == 0 {
    fmt.Println("you didn't type add")
} else if inp[0] == "add" {
    fmt.Println("you typed add")
}