How is a Cobra Flag of type `StringToStringVar` access using Viper?

Question

I am trying to develop an application in Go that accepts inputs on the command line as a string of key value pairs. To do this I am using StrngToStringVar from the Cobra library.

I am also using Viper to bind these flags to configuration, however whatever value I put it I do not seem to be able to get it from Viper.

This is the code

package main

import (
    "fmt"

    "github.com/spf13/cobra"
    "github.com/spf13/viper"

    "github.com/davecgh/go-spew/spew"
)

func main() {
    var items map[string]string
    var name string

    rootCmd := &cobra.Command{
        Use:   "cobra",
        Short: "Test options on the command line",
        Long:  ``,
        Run: func(ccmd *cobra.Command, args []string) {

            spew.Dump(viper.GetString("name"))
            spew.Println("")

            fmt.Println("GetStringMap")
            spew.Dump(viper.GetStringMap("items"))

            fmt.Println("")

            fmt.Println("GetStringMapString")
            spew.Dump(viper.GetStringMapString("items"))
        },
    }

    rootCmd.Flags().StringVar(&name, "name", "", "Name of the list")
    rootCmd.Flags().StringToStringVar(&items, "item", nil, "Map stating the items to be included")

    viper.BindPFlag("name", rootCmd.Flags().Lookup("name"))
    viper.BindPFlag("items", rootCmd.Flags().Lookup("item"))

    rootCmd.Execute()
}

If I run this with the command go run .\main.go --item shopping=apple,banana --name foobar I get the following result

(string) (len=6) "foobar"

GetStringMap
(map[string]interface {}) {
}

GetStringMapString
(map[string]string) {
}

As can be seent he output contains nothing for the items even though I set the input (I believe) correctly. I have been trying to use PR https://github.com/spf13/pflag/pull/133 to work out how to do it but I am not having any luck.

I am wondering if the binding is incorrect, but I have used CObra successfully in other projects so it is my lack of understanding as to how to reference the generated map[string]string from Cobra.

Did you try to use the variables `items` and `names` as package variables — Eduardo Pereira, Oct 18 '19 at 15:20

Azeem · Accepted Answer · 2019-10-20T07:39:51.713

As far as the binding part is concerned, it is correct. However, before processing, you can verify if a particular key exists using vipver.IsSet(), print all the available keys using viper.AllKeys() or print everything using viper.AllSettings().

Here's an example (test.go):

package main

import (
    "fmt"

    "github.com/spf13/cobra"
    "github.com/spf13/viper"
)

func main() {
    var items map[string]string

    rootCmd := &cobra.Command{
        Use: "app",
        Run: func(ccmd *cobra.Command, args []string) {

            fmt.Println("item exists?", viper.IsSet("item"))
            fmt.Println("GetString  :", viper.GetString("item"))
            fmt.Println("Keys       :", viper.AllKeys())
            fmt.Println("Settings   :", viper.AllSettings())
        },
    }

    rootCmd.Flags().StringToStringVarP(&items, "item", "i", nil, "Map stating the items to be included")
    viper.BindPFlag("item", rootCmd.Flags().Lookup("item"))
    rootCmd.Execute()
}

Output:

$ ./test.exe -i 'k=v,"a=b,c"'
item exists? true
GetString  : [k=v,"a=b,c"]
Keys       : [item]
Settings   : map[item:[k=v,"a=b,c"]]

The usage of GetStringMap() and GetStringMapString() makes more sense with other formats like JSON, YAML, etc. You can trace the execution of these functions to JSON unmarshalling calls in debugging mode.

For map conversion, you can write your own function like this (live):

func getStringMap(s string) map[string]string {
    entries := strings.Split(s, ",")

    m := make(map[string]string)
    for _, e := range entries {
        tokens := strings.Split(e, "=")
        k := strings.TrimSpace(tokens[0])
        v := strings.TrimSpace(tokens[1])
        m[k] = v
    }

    return m
}

thanks for this, the printing out of the viper settings really helped me understand what is going on. I had an issue where `./text.exe -i 'k=v,"a=b,c"` results in the error `Error: invalid argument "k=v,b=c,d" for "-i, --item" flag: d must be formatted as key=value`, however I realised that I can use multiple `-i` to add in more items. — Russell Seymour, Oct 21 '19 at 11:34
@RussellSeymour: You are welcome! :) Yes, you can use a flag multiple times to achieve the same effect. But, it should work for multiple values as well with single flag e.g. `./test.exe -i 'k=v,"a=b,c"'`. In your comment, the trailing quote `'` is missing. Was that a typo? — Azeem, Oct 21 '19 at 11:53
yes it was a typo, I did have the trailing `'` on the command line when I tested it. I do not mind that I can use `-i` multiple times, in fact I think it makes it easier to document :-). Thanks for your help. — Russell Seymour, Oct 22 '19 at 07:29

How is a Cobra Flag of type `StringToStringVar` access using Viper?

1 Answers1