The examples provided in this book are all self-contained. Every example is a full program and can be run. Most examples are short and demonstrate one specific topic. While the examples can be used as standalone programs, some of them may have limited use. They are intended to be references and used like a cookbook for building your own projects. Because each example is a self-contained main package, you can use the go build command to get an executable and go run to run the file. Here are some more details about the various options for building and running programs.
If you build a file, it will generate an executable named after the Go file. Run the following command:
go build example.go
This will give you an executable named example that could be executed like this:
You don't have to build a file and get an executable if you only want to run it. The go run option allows you to run the .go file without leaving an executable behind. You can still pass in arguments as if it was a regular executable, like this:
go run example.go arg1 arg2
If a program is split into multiple files, you can pass all of them to the build command. For example, if you have a main.go file and an utility.go file containing extra functions, you could build them by running the following command:
go build main.go utility.go
If you tried to build main.go by itself, it would not be able to find the references to the functions in utility.go.
If a package contains multiple Go files that need to be built, it is tedious to pass each file to the build command. If you run go build with no arguments inside a folder, it will attempt to build all the .go files in the directory. If one of those files contains a package main statement at the top, it will generate an executable named after the directory name. If you write a program, it is possible to write a package that contains no main file and is used only as a library to be included in other projects.
Installing a program is similar to building one but, instead of running go build, you run go install. You can run it inside a directory, pass it an absolute directory path, and pass it a directory path relative to the $GOPATH environment variable or on a file directly. Once a program has been installed, it goes into your $GOBIN, which you should have already set. You should have already added $GOBIN to your $PATH as well so that you can run the installed programs directly from your command line no matter what directory you are currently in. Installing is totally optional, but it is convenient for certain programs, especially for the ones you want to save or use frequently.