gcli generates a skeleton (codes and its directory structure) you need to start building Command Line Interface (CLI) tool by Golang right out of the box. You can use your favorite CLI framework.

Why you need gcli? Because you should focus on writing core function of CLI, not on interface. During developing CLI tool by Golang, you may find you're writing the chunk of boilerplate code for interfaces. Stop writing the same codes every time. gcli generates them and save you a large amount of time by writing such code. This is like Rails scaffold. Not only that, gcli know the best practices of golang CLI framework library which you want to use. Generated codes follows the most ideal way of using that framework, and you don't need to know about that. See the frameworks it supports now.

The following demo shows creating todo CLI application which has add, list and delete command with mitchellh/cli (Which is used for Hashicorp products) with one command. As you can see, the generated codes are go build-able from beginning.

And this video shows creating same todo CLI application with design & apply commands. This is the other way to start building new CLI application. First, it starts with creating design file by design command. In this file, you can define, CLI name, description of the CLI , framework you want to use, and commands & flags with its usages. After editing, it executes apply command to generating a project from that design file.

gcli is single command-line application. This application then takes subcommands. To check the all available commands,

$ gcli help

To get help for any specific subcommand, run it with the -h flag.

gcli has 2 main subcommand to generate the project. The one is the new command, the other is the design & apply commands. The former is for generating the project by command line one-liner, the latter is for when you want to design it in your editor before generating (It generates design file and you can generate project based on it). The following section explain, how to use these commands.

The new command tells gcli to generate CLI project with command-line one-liner,

$ gcli new [options] NAME

You must provides project name (NAME), the name will be the directory name it includes all codes and be the default binary name. By default, gcli creates a project under $GOPATH/github.com/<username> (If you don't provide username via option, it uses github.user or user.name in .gitconfig file). In option, you can set subcommand or flag it has and its description. You can also set your favorite CLI framework there. The followings are all available opntions,

-command=name, -c           Command name which you want to add.
                            This is valid only when cli pacakge support commands.
                            This can be specified multiple times. Synopsis can be
                            set after ":". Namely, you can specify command by
                            -command=NAME:SYNOPSYS. Only NAME is required.
                            You can set multiple variables at same time with ","
                            separator.

-flag=name, -f              Global flag option name which you want to add.
                            This can be specified multiple times. By default, flag type
                            is string and its description is empty. You can set them,
                            with ":" separator. Namaly, you can specify flag by
                            -flag=NAME:TYPE:DESCIRPTION. Order must be flow  this and
                            TYPE must be string, bool or int. Only NAME is required.
                            You can set multiple variables at same time with ","
                            separator.

-framework=name, -F         Cli framework name. By default, gcli use "codegangsta/cli"
                            To check cli framework you can use, run 'gcli list'.
                            If you set invalid framework, it will be failed.

-owner=name, -o             Command owner (author) name. This value is also used for
                            import path name. By default, owner name is extracted from
                            ~/.gitconfig variable.

-skip-test, -T              Skip generating *_test.go file. By default, gcli generates
                            test file If you specify this flag, gcli will not generate
                            test files.

For example, to todo CLI application which has add, list and delete command with mitchellh/cli,

$ gcli new -F mitchellh_cli -c add -c list -c delete todo

The design command tells gcli to prepare design template file (.toml). The design file defines all necessary information to generate CLI application. Some fields are filled with the ideal default value, and some have empty value. You can fill that empty filed with your favorite editor with thinking like what interface that should have or description of that and so on. You can see sample template file sample.toml.

After design, use apply command and tells gcli to generate CLI project based on the design file. The following describes this workflow.

First, generate design template file by design command,

$ gcli design [options] NAME

You must provides project name (NAME). In option, you can set subcommand or flag it has and its description. You can also set your favorite CLI framework there. You can edit these values in design file later.

Then, edit design file by your favorite $EDITOR.

$ $EDITOR <NAME>-design.toml

After that validate design by validate command to check required fields are filled,

$ gcli validate <NAME>-design.toml

Finnaly, generate CLI project with that design file by apply command,

$ gcli apply <NAME>-desigon.toml

The video for this workflow is available on Vimeo.

There are many framework (package) for buidling command line application by golang. For example, one of the most famous frameworks is codegangsta/cli. The framework helps you not writing many codes. But still you need to write many boilerplate code for that framework. And there are different way to use that framework and learning the ideal way to use is waste of time. gcli writes out with following the best practice for that framework (learn from famous tool that is built with that framework).

gcli can generate 2 types of CLI pattern. The one is sub-command pattern, the other is flag pattern. The former is flexible and you can add many behavior in one command application. The later is for simple application. You can check the all available frameworks by list command,

$ gcli list

To change framework, you can use -framework or -F option with the framework name. This option can be used for new, design and apply command. By default, codegangsta_cli will be used.

The following section will explain sub-command pattern and flag pattern.

Sub-Command pattern is the pattern that executable takes sub-command for change its behavior. git command is one example for this pattern. It takes push, pull subcommands. gcli is also this pattern. gcli supports the following frameworks for the command pattern.

(go_cmd is not framework. It only uses standard package. It generates same struct and functions that go command uses.)

Flag pattern is the pattern that executable has flag options for changing its behavior. For example, grep command is this pattern. Now gcli only supports the official flag package for this pattern.

For example, to create command it has -ignore-case option and context option (your own grep),

$ gcli new -F flag -flag=i:Bool -flag=C:Int grep

To install, use go get and make install. We tag versions so feel free to checkout that tag and compile.

$ go get -d github.com/tcnksm/gcli
$ cd $GOPATH/src/github.com/tcnksm/gcli
$ make install 

1. Fork (https://github.com/tcnksm/gcli/fork)
2. Create a feature branch
3. Commit your changes
4. Rebase your local changes against the master branch
5. Run test suite with the make test command and confirm that it passes
6. Create a new Pull Request

Taichi Nakashima