CODEWITHSUNDEEP
go
Stefano Conte
Stefano Conte

Reputation: 85

Golang : command-line-arguments undefined: variable

I want to create an external function for usage display in Golang, but I don't know how to call the flag variable. This is my actual code:

package main

import (
    "flag"
    "fmt"
    "os"
)

func Usage() {
    if ArgSend {
        fmt.Printf("Usage: SEND")
        flag.PrintDefaults()
        os.Exit(0)

    } else if ArgTest {
        fmt.Printf("Usage: -test")
        flag.PrintDefaults()
        os.Exit(0)

    } else if ArgMacro {
        fmt.Printf("Usage: -macro")
        os.Exit(0)

    } else {
        fmt.Printf("Usage of: <-test|-send|-macro>\n")
        os.Exit(0)
    }
}



func main() {

    //defaults variables
    ArgTest, ArgSend, ArgMacro  := false, false, false

    // Args parse
    flag.BoolVar(&ArgTest, "-test", false, "run test mode")
    flag.BoolVar(&ArgSend, "-send", false, "run send mode")
    flag.BoolVar(&ArgMacro, "-macro", false, "run macro mode")

    flag.Parse()

    Usage()
}

Return this error:

F:\dev\GoLang\gitlab\EasySend\tmp>go run stackoverflow.go -test
# command-line-arguments
.\stackoverflow.go:10:5: undefined: ArgSend
.\stackoverflow.go:15:12: undefined: ArgTest
.\stackoverflow.go:20:12: undefined: ArgMacro

How can I check flag parse if ArgSend is true/false?

Upvotes: 0

Views: 9137

Answers (1)

SwiftD
SwiftD

Reputation: 6079

A couple of things wrong in your example:

  • The variables you are trying to use in your usage function are not in scope since all your flag variables are declared inside main (.
  • The flag variables themselves are of the wrong type, you should use types from the flag package
  • Others errors include, adding '-' at the front of flag text (2nd arg) and not dereferencing the flag variables (they will be pointers)

There is a good example here: golang flags example and you should check godocs on flags particularly for default behavior and custom usage functions, if you have trouble modifying the example then ask again here

Updated: Sorry, as Peter pointed to in comments my answer is a little muddled and incorrect.

To Clarify, in the example provided in the "golang flags example" link given flag.Bool is used. When using flag.Bool a pointer is returned.

In the Question you use flag.BoolVar which allows you to reference a bool value. your use of flag.BoolVar in the question is in fact correct.

So all you need to do is address the scoping issue, not really clear what you are trying to do with your Usage but here is a working example that should clarify:

Note: in this example the flag vars could have stayed inside main as they are not required in the Usage function

package main

import (
    "flag"
    "fmt"
    "os"
)

func Usage() {
    // custom usage (help) output here if needed
    fmt.Println("")
    fmt.Println("Application Flags:")
    flag.PrintDefaults()
    fmt.Println("")
}

var ArgTest, ArgSend, ArgMacro bool

func main() {

    // Args parse
    flag.BoolVar(&ArgTest, "test", false, "run test mode")
    flag.BoolVar(&ArgSend, "send", false, "run send mode")
    flag.BoolVar(&ArgMacro, "macro", false, "run macro mode")

    flag.Parse()

    // assign custom usage function (will be shown by default if -h or --help flag is passed)
    flag.Usage = Usage

    // if no flags print usage (not default behaviour)
    if len(os.Args) == 1 {
        Usage()
    }

    fmt.Printf("ArgTest val: %t\n", ArgTest)
    fmt.Printf("ArgSend val: %t\n", ArgSend)
    fmt.Printf("ArgMacro val: %t\n", ArgMacro)

}

Upvotes: 1

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