Getting Started

Introduction

Go is an open source project, distributed under a BSD-style license. This document explains how to check out the sources, build them on your own machine, and run them.

There are two distinct ways to experiment with Go. This document focuses on the gc Go compiler and tools (6g, 8g etc.). For information on how to use gccgo, a more traditional compiler using the GCC back end, see Setting up and using gccgo.

The Go compilers support three instruction sets. There are important differences in the quality of the compilers for the different architectures.

amd64 (a.k.a. x86-64); 6g,6l,6c,6a: The most mature implementation. The compiler has an effective optimizer (registerizer) and generates good code (although gccgo can do noticeably better sometimes).
386 (a.k.a. x86 or x86-32); 8g,8l,8c,8a: Comparable to the amd64 port.
arm (a.k.a. ARM); 5g,5l,5c,5a: Incomplete. It only supports Linux binaries, the optimizer is incomplete, and floating point uses the VFP unit. However, all tests pass. Work on the optimizer is continuing. Tested against a Nexus One.

Except for things like low-level operating system interface code, the run-time support is the same in all ports and includes a mark-and-sweep garbage collector (a fancier one is in the works), efficient array and string slicing, support for segmented stacks, and a strong goroutine implementation.

The compilers can target the FreeBSD, Linux, and OS X (a.k.a. Darwin) operating systems. (A port to Microsoft Windows is in progress but incomplete. See the Windows Port page for details.) The full set of supported combinations is listed in the discussion of environment variables below.

Install C tools, if needed

The Go tool chain is written in C. To build it, you need these programs installed:

GCC,
the standard C libraries,
the parser generator Bison,
GNU make (version 3.81 or later), and
awk.

On OS X, they can be installed as part of Xcode.

On Ubuntu/Debian, use sudo apt-get install bison gawk gcc libc6-dev make. If you want to build 32-bit binaries on a 64-bit system you'll also need the libc6-dev-i386 package.

Install Mercurial, if needed

To perform the next step you must have Mercurial installed. (Check that you have an hg command.) This suffices to install Mercurial on most systems:

sudo easy_install mercurial

(On Ubuntu/Debian, you might try

apt-get install python-setuptools
python-dev build-essential

first. The Mercurial in your distribution's package repository will most likely be old and broken.)

If that fails, try installing manually from the Mercurial Download page.

Mercurial versions 1.7.x and up require the configuration of Certification Authorities (CAs). Error messages of the form:

warning: go.googlecode.com certificate with fingerprint b1:af: ... bc not verified (check hostfingerprints or web.cacerts config setting)

when using Mercurial indicate that the CAs are missing. Check your Mercurial version (hg --version) and configure the CAs if necessary.

Fetch the repository

Go will install to a directory named go. Change to the directory that will be its parent and make sure the go directory does not exist. Then check out the repository:

$ hg clone -u release https://go.googlecode.com/hg/ go

Install Go

To build the Go distribution, run

$ cd go/src
$ ./all.bash

If all goes well, it will finish by printing output like:

ALL TESTS PASSED

---
Installed Go for linux/amd64 in /home/you/go.
Installed commands in /home/you/go/bin.
*** You need to add /home/you/go/bin to your $PATH. ***
The compiler is 6g.

where the details on the last few lines reflect the operating system, architecture, and root directory used during the install.

For more information about ways to control the build, see the discussion of environment variables below.

Writing programs

Given a file file.go, compile it using

$ 6g file.go

6g is the Go compiler for amd64; it will write the output in file.6. The ‘6’ identifies files for the amd64 architecture. The identifier letters for 386 and arm are ‘8’ and ‘5’. That is, if you were compiling for 386, you would use 8g and the output would be named file.8.

To link the file, use

$ 6l file.6

and to run it

$ ./6.out

A complete example:

$ cat >hello.go <<EOF
package main

import "fmt"

func main() {
	fmt.Printf("hello, world\n")
}
EOF
$ 6g hello.go
$ 6l hello.6
$ ./6.out
hello, world
$

There is no need to list hello.6's package dependencies (in this case, package fmt) on the 6l command line. The linker learns about them by reading hello.6.

To build more complicated programs, you will probably want to use a Makefile. There are examples in places like go/src/cmd/godoc/Makefile and go/src/pkg/*/Makefile. The document about contributing to the Go project gives more detail about the process of building and testing Go programs.

What's next

Start by taking A Tour of Go or reading the Go Tutorial.

Build a web application by following the Wiki Codelab.

Read Effective Go to learn about writing idiomatic Go code.

For the full story, consult Go's extensive documentation.

Keeping up with releases

The Go project maintains two stable tags in its Mercurial repository: release and weekly. The weekly tag is updated about once a week, and should be used by those who want to track the project's development. The release tag is given, less often, to those weekly releases that have proven themselves to be robust.

Most Go users will want to keep their Go installation at the latest release tag. New releases are announced on the golang-announce mailing list.

To update an existing tree to the latest release, you can run:

$ cd go/src
$ hg pull
$ hg update release
$ ./all.bash

To use the weekly tag run hg update weekly instead.

Community resources

For real-time help, there may be users or developers on #go-nuts on the Freenode IRC server.

The official mailing list for discussion of the Go language is Go Nuts.

Bugs can be reported using the Go issue tracker.

For those who wish to keep up with development, there is another mailing list, golang-checkins, that receives a message summarizing each checkin to the Go repository.

Environment variables

The Go compilation environment can be customized by environment variables. None are required by the build, but you may wish to set them to override the defaults.

$GOROOT

The root of the Go tree, often $HOME/go. This defaults to the parent of the directory where all.bash is run. If you choose not to set $GOROOT, you must run gomake instead of make or gmake when developing Go programs using the conventional makefiles.

$GOROOT_FINAL

The value assumed by installed binaries and scripts when $GOROOT is not set. It defaults to the value used for $GOROOT. If you want to build the Go tree in one location but move it elsewhere after the build, set $GOROOT_FINAL to the eventual location.

$GOOS and $GOARCH

The name of the target operating system and compilation architecture. These default to the values of $GOHOSTOS and $GOHOSTARCH respectively (described below).

Choices for $GOOS are linux, freebsd, darwin (Mac OS X 10.5 or 10.6), and windows (Windows, an incomplete port). Choices for $GOARCH are amd64 (64-bit x86, the most mature port), 386 (32-bit x86), and arm (32-bit ARM, an incomplete port). The valid combinations of $GOOS and $GOARCH are:

`$GOOS`	`$GOARCH`
`darwin`	`386`
`darwin`	`amd64`
`freebsd`	`386`
`freebsd`	`amd64`
`linux`	`386`
`linux`	`amd64`
`linux`	`arm`	incomplete
`windows`	`386`	incomplete

$GOHOSTOS and $GOHOSTARCH

The name of the host operating system and compilation architecture. These default to the local system's operating system and architecture.

Valid choices are the same as for $GOOS and $GOARCH, listed above. The specified values must be compatible with the local system. For example, you should not set $GOHOSTARCH to arm on an x86 system.

$GOBIN

The location where binaries will be installed. The default is $GOROOT/bin. After installing, you will want to arrange to add this directory to your $PATH, so you can use the tools.

$GOARM (arm, default=6)

The ARM architecture version the run-time libraries should target. ARMv6 cores have more efficient synchronization primitives. Setting $GOARM to 5 will compile the run-time libraries using just SWP instructions that work on older architectures as well. Running v6 code on an older core will cause an illegal instruction trap.

Note that $GOARCH and $GOOS identify the target environment, not the environment you are running on. In effect, you are always cross-compiling. By architecture, we mean the kind of binaries that the target environment can run: an x86-64 system running a 32-bit-only operating system must set GOARCH to 386, not amd64.

If you choose to override the defaults, set these variables in your shell profile ($HOME/.bashrc, $HOME/.profile, or equivalent). The settings might look something like this:

export GOROOT=$HOME/go
export GOARCH=386
export GOOS=linux

The Go Programming Language