Creating Go CLI Application using Cobra

Pre-requisites before getting started :-

1. You must have Golang Installed on your device. https://golang.org/doc/install follow this link to download and use go version command to check for the installed version (I'm using go version go1.14.3 darwin/amd64)
2. Cobra Library - which is a CLI library for Go that empowers applications. Get it using go get -u github.com/spf13/cobra/cobra. And to include cobra in your project use import "github.com/spf13/cobra"
3. Code Editor

Setting up GOROOT and GOPATH

1. GOROOT is a variable that defines where your Go SDK is located. Generally /usr/local/go
2. GOPATH is a variable that defines the root of your workspace. GOPATH stores your code base and all the files that are necessary for your development. You can use another directory as your workspace by configuring GOPATH for different scopes. It contains following folders src/: location of Go source code (for example, .go, .c, .g, .s). pkg/: location of compiled package code (for example, .a). bin/: location of compiled executable programs built by Go. GOPATH can have more than one values. Setting up GOPATH in .bash_profile

export GOROOT="/usr/local/go"
export PATH="$GOROOT/bin:$PATH"
export GOPATH="/Users/mohitdtumce/Documents/learn_go/golib"
export PATH="$GOPATH/bin:$PATH"
export GOPATH="$GOPATH:/Users/mohitdtumce/Documents/learn_go/basic_cobra"

As you'll notice, I've provided two paths in GOPATH - one for libraries and another for code development.

Setting up project

• Module - A module is a collection of Go packages stored in a file tree with a go.mod file at its root. The go.mod file defines the module’s module path, which is also the import path used for the root directory, and its dependency requirements, which are the other modules needed for a successful build.

cd  ~/Documents/learn_go/basic_cobra
go mod init learn_cobra

Add Cobra library in the project :-

go get -u github.com/spf13/cobra/cobra
cobra init --pkg-name=learn_cobra

main.go is the starting point of the application. Use go run main.go command to run the program.

Cobra Commands

• Cobra is useful because it provides
  • Automatic flags recognition and argument parsing.
  • Bash autocomplete for application.
  • Easy to add and remove subcommands.
  • Intelligent suggestions.
• Open the terminal and go install learn_cobra will create binary executable file of the program inside $GOPATH/bin folder.
• Basic Command Structure in Cobra ROOTCMD SUBCOMMAND ARG --FLAG. Every cobra application has a root command (inside cmd/root.go) and then there can be multiple sub commands. Our app name is learn_cobra and if you'll notice inside root.go, it is also the rootCmd. So use learn_cobra $SUBCOMMAND $ARG --$FLAG to run any subcommand.
• To add sub-commands
  • cobra add list to generate the list of all the commands
  • cobra add cmd_name adds a new command cmdName.go inside cmd/ folder.