create cli by cobra

install

cd to ../golang.org/x

git clone https://github.com/golang/text
git clone https://github.com/golang/sys

download github.com/spf13/cobra/cobra
cd to its dir
then open cmd & type

go install github.com/spf13/cobra/cobra

then use it:

cobra init mycalc

Cobra-based application structure:

▾ appName/
    ▾ cmd/
        root.go
    main.go

cobra main.go structure:

package main

import (
  "mycalc/cmd"
)

func main() {
  cmd.Execute()
}

when you run it, it will reports error:

G:\go-work\bin\mycalc>go run main.go
main.go:18:8: cannot find package "go-work/bin/my-calc/cmd" in any of:
        c:\go\src\go-work\bin\my-calc\cmd (from $GOROOT)
        G:\go-work\src\go-work\bin\my-calc\cmd (from $GOPATH)

⚠️so you copy the whole package to $GOPATH, then

G:\go-work\bin\mycalc>go install mycalc
G:\go-work\bin\mycalc>go run main.go
Hello CLI

G:\go-work\bin>mycalc
Hello CLI

the command in root.go is called rootCmd.

the cli flow

1. edit root.go

   func init() {
        fmt.Println("inside init")
        cobra.OnInitialize(initConfig)
   ...

2. edit main.go

   func main() {
        fmt.Println("inside main")
        cmd.Execute()
   }

   and it will shows this:

   G:\go-work\bin>mycalc
   inside init
   inside main
   inside initConfig
   inside initConfig
   Hello CLI

   Should notice two types of flags: Persistent flags & Local flags

add cli:

1. add num
   create a command named add, navigate to the project

   G:\go-work\src\mycalc>cobra add add
   add created at G:\go-work\src\mycalc

   rebuild the binary using go install mycalc and run mycalc add.

   G:\go-work\src\mycalc>go install mycalc

G:\go-work\bin>mycalc add
add called

2. modify it to add a series of numbers
   to add numbers, fisrt have to convert the string into int then returan the result.

   import (
       ...
       "strconv"
   )

3. inside the add.go, create a new addInt function.

   func addInt(args []string) {
       var sum int
       // the first return value is index of args, we can omit it using _ 
       for _, ival := range args {
       // strconv is the library used for type conversion, for string
       // to int conversion Atio method is udes.
           itemp, err := strconv.Atoi(ival)
           if err != nil {
               fmt.Println(err)
           }
           sum = sum + itemp
       }
       fmt.Printf("Addition of numbers %s is %d, args, sum)
   }

4. update RUN func

   ...
   addInt(args)
   ...

5. rebuild

   G:\go-work\bin>mycalc add a bc 8
   strconv.Atoi: parsing "a": invalid syntax
   strconv.Atoi: parsing "bc": invalid syntax
   Addition of numbers [a bc 8] is 8

achieve float calc by using flag

1. create a local flag in init

//add.go
func init() {
    rootCmd.AddCommand(addCmd)
    addCmd.Flags().BoolP("float", "f",false,"Add Floating Numbers")
}

2. create a addFloat func in add.go
   //add.go
   func addFloat(args []string) {
   var sum float64
   for _, fval := range args {
   ftemp, err := strconv.ParseFloat(fval,64)
   if err != nil {
   fmt.Println(err)
   }
   sum = sum + ftemp
   }
   fmt.Printf(“sum of floating nums %s is %f”, args,sum)
   }

   3. create a addFloat func in addCmd RUN func
   ``` bash
   // add.go
   // addCmd
   Run: func(cmd *cobra.Command, args []string) {
       // get the flag value, its default value is false
       fstatus, _ := cmd.Flags().GetBool("float")
       if fstatus {
           addFloat(args)
       } else {
           addInt(args)
       }
   },

select even numbers & add them

cobra add even

1. init in even.go

   //even.go
   func init() {
       addCmd.AddCommand(evenCmd)
   ...
   }

2. update evenCmd struct variable’s RUN method

   //even.go
   Run: func(cmd *bobra.Command, args []string) {
   
       var evenSum int
       for _, ival := range args {
           itemp, _ := strconv.Atoi(ival)
           if itemp%2 == 0 {
               evenSum = evenSum + itemp
           }
       }
       fmt.Printf("the even addition of %s is %d", args, evenSum)
   },

select old numbers & add them

//odd.go
...
if itemp%2 != 0 
...