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.

Environment variables

The Go compilation environment can be customized by five 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. Although this variable is optional, the examples and typescripts below use it as shorthand for the location where you installed Go. 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 local system's operating system and architecture.

Choices for $GOOS are linux, freebsd, darwin (Mac OS X 10.5 or 10.6), and nacl (Native Client, 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

nacl 386

$GOBIN

	`$GOOS`	`$GOARCH`
	`darwin`	`386`
	`darwin`	`amd64`
	`freebsd`	`386`
	`freebsd`	`amd64`
	`linux`	`386`
	`linux`	`amd64`
	`linux`	`arm`
	`nacl`	`386`

The location where binaries will be installed. The default is $HOME/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 runtime libraries should target. ARMv6 cores have more efficient synchronization primitives. Setting $GOARM to 5 will compile the runtime 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=amd64  # optional
export GOOS=linux    # optional

Double-check them by listing your environment. (You will need to launch a new shell or terminal window for the changes to take effect.)

$ env | grep '^GO'

Ports

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. Not as well soaked but should be nearly as solid.
arm (a.k.a. ARM); 5g,5l,5c,5a: It's got a couple of outstanding bugs but is improving. Tested against QEMU and an android phone. Only supports Linux binaries.

Except for things like low-level operating system interface code, the runtime 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.

See the separate gccgo document for details about that compiler and environment.

Install C tools, if needed

The Go tool chain is written in C. To build it, you need to have GCC, the standard C libraries, the parser generator Bison, make, awk, and the text editor ed installed. On OS X, they can be installed as part of Xcode. On Linux, use

$ sudo apt-get install bison gcc libc6-dev ed gawk make

(or the equivalent on your Linux distribution).

Fetch the repository

If you do not have Mercurial installed (you do not have an hg command), this command:

$ sudo easy_install mercurial

works on most systems. (On Ubuntu/Debian, you might try apt-get install python-setuptools python-dev build-essential gcc first.) If that fails, visit the Mercurial Download page.

Make sure the $GOROOT directory does not exist or is empty. Then check out the repository:

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

Install Go

To build the Go distribution, run

$ cd $GOROOT/src
$ ./all.bash

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

--- cd ../test
N known bugs; 0 unexpected bugs

---
Installed Go for darwin/amd64 in /Users/you/go; the compiler is 6g.

where N is a number that varies from release to release and the details on the last line will reflect the operating system, architecture, and root directory used during the install.

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 $GOROOT/src/cmd/godoc/Makefile and $GOROOT/src/pkg/*/Makefile. The document about contributing to the Go project gives more detail about the process of building and testing Go programs.

Keeping up with releases

New releases are announced on the Go Nuts mailing list. To update an existing tree to the latest release, you can run:

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

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.