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# cli.go
cli.go is simple, fast, and fun package for building command line apps in Go. The goal is to enable developers to write fast and distributable command line applications in an expressive way.

## Overview
Command line apps are usually so tiny that there is absolutely no reason why your code should *not* be self-documenting. Things like generating help text and parsing command flags/options should not hinder productivity when writing a command line app.

This is where cli.go comes into play. cli.go makes command line programming fun, organized, and expressive!

## Installation
Make sure you have the a working Go environment (go 1.1 is *required*). [See the install instructions](http://golang.org/doc/install.html).

To install cli.go, simply run:
```
$ go get github.com/codegangsta/cli
```

Make sure your PATH includes to the `$GOPATH/bin` directory so your commands can be easily used:
```
export PATH=$PATH:$GOPATH/bin
```

## Getting Started
One of the philosophies behind cli.go is that an API should be playful and full of discovery. So a cli.go app can be as little as one line of code in `main()`. 

``` go
package main

import "os"
import "github.com/codegangsta/cli"

func main() {
  cli.NewApp().Run(os.Args)
}
```

This app will run and show help text, but is not very useful. Let's give an action to execute and some help documentation:

``` go
package main

import "os"
import "github.com/codegangsta/cli"

func main() {
  app := cli.NewApp()
  app.Name = "boom"
  app.Usage = "make an explosive entrance"
  app.Action = func(c *cli.Context) {
    println("boom! I say!")
  }
  
  app.Run(os.Args)
}
```

Running this already gives you a ton of functionality, plus support for things like subcommands and flags, which are covered below.

## Example

Being a programmer can be a lonely job. Thankfully by the power of automation that is not the case! Let's create a greeter app to fend off our demons of loneliness!

``` go
/* greet.go */
package main

import "os"
import "github.com/codegangsta/cli"

func main() {
  app = cli.NewApp()
  app.Name = "greet"
  app.Usage = "fight the loneliness!"
  app.Action = func(c *cli.Context) {
    println("Hello friend!")
  }
  
  app.Run(os.Args)
}
```

Install our command to the `$GOPATH/bin` directory:

```
$ go install
```

Finally run our new command:

```
$ greet
Hello friend!
```

cli.go also generates some bitchass help text:
```
$ greet help
NAME:
    greet - fight the loneliness!

USAGE:
    greet [global options] command [command options] [arguments...]

VERSION:
    0.0.0

COMMANDS:
    help, h  Shows a list of commands or help for one command

GLOBAL OPTIONS
    --version	Shows version information
```

### Arguments
You can lookup arguments by calling the `Args` function on cli.Context.

``` go
...
app.Action = func(c *cli.Context) {
  println("Hello", c.Args()[0])
}
...
```

### Flags
Setting and querying flags is simple.
``` go
...
app.Flags = []cli.Flag {
  cli.StringFlag{"lang", "english", "language for the greeting"},
}
app.Action = func(c *cli.Context) {
  if c.String("lang") == "spanish" {
    println("Hola", c.Args()[0])
  } else {
    println("Hello", c.Args()[0])
  }
}
...
```

### Subcommands

Subcommands can be defined for a more git-like command line app.
```go
...
app.Commands = []cli.Command{
  {
    Name:      "add",
    ShortName: "a",
    Usage:     "add a task to the list",
    Action: func(c *cli.Context) {
      println("added task: ", c.Args()[0])
    },
  },
  {
    Name:      "complete",
    ShortName: "c",
    Usage:     "complete a task on the list",
    Action: func(c *cli.Context) {
      println("completed task: ", c.Args()[0])
    },
  },
}
...
```

## About
cli.go is written by none other than the [Code Gangsta](http://codegangsta.io)