In order to proceed with all the recipes in this chapter, configure your environment according to these steps:

1. Download and install Go 1.12.6 or greater on youroperatingsystem athttps://golang.org/doc/install.
2. Open a Terminal or console application and create and navigate to a project directory such as ~/projects/go-programming-cookbook. All of our code will be run and modified from this directory.
3. Clone the latest code into ~/projects/go-programming-cookbook-original and work from that directory rather than typing the examples manually:

          $ git clone git@github.com:PacktPublishing/Go-Programming-Cookbook-Second-Edition.git go-programming-cookbook-original
        

The flag package makes it simple to add command-line flag arguments to a Go application. It has a few shortcomings—you tend to duplicate a lot of code in order to add shorthand versions of flags, and they're ordered alphabetically from the help prompt. There are a number of third-party libraries that attempt to address these shortcomings, but this chapter will focus on the standard library version and not on those libraries.

How to do it...

These steps cover writing and running your application:

1. From your Terminal or console application,createa new directory called~/projects/go-programming-cookbook/chapter2/flags.
2. Navigate to this directory.
3. Run the following command:

          $ go mod init github.com/PacktPublishing/Go-Programming-Cookbook-Second-Edition/chapter2/flags

        

You should see a file calledgo.modthat contains the following:

module...

The flags from the previous recipe are a type of command-line argument. This chapter will expand on other uses for these arguments by constructing a command that supports nested subcommands. This will demonstrate flagsets and also use positional arguments that are passed into your application.

Like the previous recipe, this one requires a main function to run. There are a number of third-party packages that deal with complex nested arguments and flags, but we'll investigate how to do this using only the standard library.

How to do it...

These steps cover writing and running your application:

1. From your Terminal or console application,createa new directory called~/projects/go-programming-cookbook/chapter2/cmdargs.
2. Navigate to this directory.
3. Run the following command:

          $ go mod init github.com/PacktPublishing/Go-Programming-Cookbook-Second-Edition/chapter2...

Environment variables are another way that you can pass state into an application beyond reading data in from a file or passing it explicitly over the command line. This recipe will explore some very basic getting and setting of environment variables and then work with the highly useful third-party library envconfig (https://github.com/kelseyhightower/envconfig).

We'll build an application that can read a config file via JSON or through environment variables. The next recipe will explore alternative formats, including TOML and YAML.

How to do it...

These steps cover writing and running your application:

1. From your Terminal or console application,createa new directory called~/projects/go-programming-cookbook/chapter2/envvar.
2. Navigate to this directory.
3. Run the following command:

          $ go mod init github.com/PacktPublishing/Go-Programming-Cookbook...

There are many configuration formats that Go, with the use of third-party libraries, supports. Three of the most popular data formats are TOML, YAML, and JSON. Go can support JSON out of the box, and the others have clues on how to marshal/unmarshal or encode/decode data for these formats. These formats have many benefits beyond configuration, but this chapter will largely focus on converting a Go structure in the form of a configuration structure. This recipe will explore basic input and output using these formats.

These formats also provide an interface by which Go and applications written in other languages can share the same configuration. There are also a number of tools that deal with these formats and simplify working with them.

How to do it...

These steps cover writing and running your application:

1. From your Terminal or console application,createa new directory called~/projects...

Unix pipes are useful when we are passing the output of one program to the input of another. For example, take a look at the following code:

          $ echo "test case" | wc -l
          

             1
        

In a Go application, the left-hand side of the pipe can be read in using os.Stdin, which acts like a file descriptor. To demonstrate this, this recipe will take an input on the left-hand side of a pipe and return a list of words and their number of occurrences. These words will be tokenized on white space.

How to do it...

These steps cover writing and running your application:

1. From your Terminal or console application,createa new directory called~/projects/go-programming-cookbook/chapter2/pipes.
2. Navigate to this directory.
3. Run the following command:

          $ go mod init github.com/PacktPublishing/Go-Programming-Cookbook-Second-Edition/chapter2...

Signals are a useful way for the user or the OS to kill your running application. Sometimes, it makes sense to handle these signals in a more graceful way than the default behavior. Go provides a mechanism to catch and handle signals. In this recipe, we'll explore the handling of signals through the use of a signal that handles the Go routine.

How to do it...

These steps cover writing and running your application:

1. From your Terminal or console application,createa new directory called~/projects/go-programming-cookbook/chapter2/signals.
2. Navigate to this directory.
3. Run the following command:

          $ go mod init github.com/PacktPublishing/Go-Programming-Cookbook-Second-Edition/chapter2/signals

        

You should see a file calledgo.modthat contains the following:

module github.com/PacktPublishing/Go-Programming-Cookbook-Second-Edition/chapter2/signals

...

Coloring an ANSI terminal application is handled by a variety of code before and after a section of text you want colored. This recipe will explore a basic coloring mechanism that colors text red or plain. For a complete application, take a look at https://github.com/agtorre/gocolorize, which supports many more colors and text types, and also implements the fmt.Formatter interface for ease of printing.

How to do it...

These steps cover writing and running your application:

1. From your Terminal or console application,createa new directory called~/projects/go-programming-cookbook/chapter2/ansicolor.
2. Navigate to this directory.
3. Run the following command:

          $ go mod init github.com/PacktPublishing/Go-Programming-Cookbook-Second-Edition/chapter2/ansicolor

        

You should see a file calledgo.modthat contains the following:

module github...