Ricardo Gerardi - Powerful Command-Line Applications in Go

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To my beloved wife Kassia. My best friend, my greatest supporter. Sadly she passed away due to cancer before seeing this book completed.

To my four incredible daughters Gisele, Livia, Elena, and Alice. The reason for everything.

In 2012 I began a journey of experimentation in investigating a new language,Go, which was born at Google and had just reached the 1.0 milestone. I learnbest by building so I was looking for a project meaningful enough to actuallylearn Go. I was growing frustrated with the increasing cost andcomplexity of my WordPress-powered blog with entirely static content anddecided that building a static site generator was the project for me to learnGo. I began writing my first Go project, Hugo.

Having previously designed several CMSs and command-line tools, I had a goodsense of what I wanted to build. I opened up a terminal and began by typingcommands for this not yet existing program to effectively sketch out how theuser interface would be shaped. With this sketch in hand, I then began theprocess of building the application. As I was inexperienced with Go, I hoped tolean heavily on existing libraries, but as this was the dawn of the Goecosystem, more often than not, the libraries I needed didnt exist.

Unable to find the right library to support the design pattern of [application] [command] [flag] [argument], I set out to write it myself. I also needed config file management as there was too much configurability to anticipate everything passed via the command line. As my goal was building Hugo, these were just Hugo packages initially, but I thought maybe someone else would benefit from this functionality too, and I pulled them out into standalone libraries and named them Cobra of this book.

Through the experience of building Hugo, Cobra, and Viper, I had arevelation: while Go was initially targeted at large-scale server applications,the Go creators had developed a language perfectly suited for command-linetools. It had everything you needed and most of what you wanted:

• Static compilation, which created executables with no local dependencies: no runtimes or libraries needed. What could be easier to install than one file?

• Cross-compilation, eliminating the need for build farms.

• Lightning-fast builds so quick that it felt like a dynamic language.

• Native concurrency, enabling your applications to take full advantage of multicore machines.

Go had nearly all the advantages of a dynamic language during development and all the advantages of a compiled language during execution, plus additional unique advantages. In short, Go is uniquely perfect for both building and running command-line applications.