The Go Command

Introduction#

The go command is a command-line program that allows for the management of Go development. It enables building, running, and testing code, as well as a variety of other Go-related tasks.

Go Run

go run will run a program without creating an executable file. Mostly useful for development. run will only execute packages whose package name is main.

To demonstrate, we will use a simple Hello World example main.go:

package main

import fmt

func main() {
    fmt.Println("Hello, World!")
}

Execute without compiling to a file:

go run main.go

Output:

Hello, World!

Run multiple files in package

If the package is main and split into multiple files, one must include the other files in the run command:

go run main.go assets.go

Go Build

go build will compile a program into an executable file.

To demonstrate, we will use a simple Hello World example main.go:

package main

import fmt
    
func main() {
    fmt.Println("Hello, World!")
}

Compile the program:

go build main.go

build creates an executable program, in this case: main or main.exe. You can then run this file to see the output Hello, World!. You can also copy it to a similar system that doesn’t have Go installed, make it executable, and run it there.

Specify OS or Architecture in build:

You can specify what system or architecture to build by modifying the env before build:

env GOOS=linux go build main.go # builds for Linux
env GOARCH=arm go build main.go # builds for ARM architecture

Build multiple files

If your package is split into multiple files and the package name is main (that is, it is not an importable package), you must specify all the files to build:

go build main.go assets.go # outputs an executable: main

Building a package

To build a package called main, you can simply use:

go build . # outputs an executable with name as the name of enclosing folder

Go Clean

go clean will clean up any temporary files created when invoking go build on a program. It will also clean files left over from Makefiles.

Go Fmt

go fmt will format a program’s source code in a neat, idiomatic way that is easy to read and understand. It is recommended that you use go fmt on any source before you submit it for public viewing or committing into a version control system, to make reading it easier.

To format a file:

go fmt main.go

Or all files in a directory:

go fmt myProject

You can also use gofmt -s (not go fmt) to attempt to simplify any code that it can.

gofmt (not go fmt) can also be used to refactor code. It understands Go, so it is more powerful than using a simple search and replace. For example, given this program (main.go):

package main

type Example struct {
    Name string
}

func (e *Example) Original(name string) {
    e.Name = name
}

func main() {
    e := &Example{"Hello"}
    e.Original("Goodbye")
}

You can replace the method Original with Refactor with gofmt:

gofmt -r 'Original -> Refactor' -d main.go

Which will produce the diff:

-func (e *Example) Original(name string) {
+func (e *Example) Refactor(name string) {
     e.Name = name
 }
 
 func main() {
     e := &Example{"Hello"}
-    e.Original("Goodbye")
+    e.Refactor("Goodbye")
 }

Go Get

go get downloads the packages named by the import paths, along with their dependencies. It then installs the named packages, like ‘go install’. Get also accepts build flags to control the installation.

go get github.com/maknahar/phonecountry

When checking out a new package, get creates the target directory $GOPATH/src/<import-path>. If the GOPATH contains multiple entries, get uses the first one. Similarly, it will install compiled binaries in $GOPATH/bin.

When checking out or updating a package, get looks for a branch or tag that matches the locally installed version of Go. The most important rule is that if the local installation is running version “go1”, get searches for a branch or tag named “go1”. If no such version exists it retrieves the most recent version of the package.

When using go get, the -d flag causes it to download but not install the given package. The -u flag will allow it to update the package and its dependencies.

Get never checks out or updates code stored in vendor directories.

Go env

go env [var ...] prints go environment information.

By default it prints all the information.

$go env

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/vikashkv/work"
GORACE=""
GOROOT="/usr/local/Cellar/go/1.7.4_1/libexec"
GOTOOLDIR="/usr/local/Cellar/go/1.7.4_1/libexec/pkg/tool/darwin_amd64"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/xf/t3j24fjd2b7bv8c9gdr_0mj80000gn/T/go-build785167995=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
CGO_ENABLED="1"

If one or more variable names is given as arguments, it prints the value of each named variable on its own line.

$go env GOOS GOPATH

darwin
/Users/vikashkv/work