Can command line flags in Go be set to mandatory?

Question

Is there a way how to set that certain flags are mandatory, or do I have to check for their presence on my own?

Answer 1

I agree with this solution but, in my case default values are usually environment values. For example,

dsn := flag.String("dsn", os.Getenv("MYSQL_DSN"), "data source name")

And in this case, I want to check if the values are set from invocation (usually local development) or environment var (prod environment).

So with some minor modifications, it worked for my case.

Using flag.VisitAll to check the value of all flags.

required := []string{"b", "s"}
flag.Parse()

seen := make(map[string]bool)
flag.VisitAll(func(f *flag.Flag) {
    if f.Value.String() != "" {
        seen[f.Name] = true
    }
})
for _, req := range required {
    if !seen[req] {
        // or possibly use `log.Fatalf` instead of:
        fmt.Fprintf(os.Stderr, "missing required -%s argument/flag\n", req)
        os.Exit(2) // the same exit code flag.Parse uses
    }
}

Test example in plauground