Retrieving go command-line Flag values from urfave/cli v2

Question

I'm building an golang app to upload some docs to a webserver. The app is a single go file called deploy_docs.go (run make build to build the application).

I'm somewhat new to go, so please keep that in mind if this is a dumb question ;-).

The app should be called like this:

bin/deploy_docs --dochost foo.bar.local

I am parsing CLI arguments in buildAppInstance(), which should assign the CLI value of --dochost to &dochost in buildAppInstance().

The problem is that I never get anything assigned to &dochost; I'm not sure why... I don't think this is scope problem but I don't know how urfave/cli should work otherwise.

Can someone explain why &dochost never gets populated by --dochost?

Answer 1

You should call (*App).Run to make it parse arguments. See the demo below:

package main

import (
    "log"
    "os"
    "time"

    "github.com/urfave/cli/v2"
)

var dochost string = ""

func buildAppInstance() (appInst *cli.App) {
    appInst = &cli.App{
        Name:     "deploy_docs",
        Version:  "0.0.2",
        Compiled: time.Now(),
        Authors: []*cli.Author{
            {
                Name:  "Mike Pennington",
                Email: "[email protected]",
            },
        },
        Flags: []cli.Flag{
            &cli.StringFlag{
                Name:        "dochost",
                Value:       "127.0.0.1",
                Usage:       "FQDN or IPv4 of the documentation host",
                Destination: &dochost,
            },
        },
        Action: func(cCtx *cli.Context) (err error) {
            log.Println("Starting cli.Context action")
            if cCtx.NArg() == 0 {
                log.Fatal("No CLI arguments detected!")
            }
            log.Printf("args: %+v", cCtx.Args())
            return nil
        },
    }
    return appInst
}

func main() {
    app := buildAppInstance()
    log.Printf("dochost before Run: %q", dochost)
    if err := app.Run(os.Args); err != nil {
        panic(err)
    }
    log.Printf("dochost after Run: %q", dochost)
}

$ go run . --dochost foo.bar.local other args
2023/06/26 23:37:43 dochost before Run: ""
2023/06/26 23:37:43 Starting cli.Context action
2023/06/26 23:37:43 args: &[other args]
2023/06/26 23:37:43 dochost after Run: "foo.bar.local"