<!-- Getting Started -->

<h2 id="introduction">Introduction</h2>

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

<div class="detail">

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

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

<dl>
<dt>
	<code>amd64</code> (a.k.a. <code>x86-64</code>); <code>6g,6l,6c,6a</code>
</dt>
<dd>
	The most mature implementation.  The compiler has an effective optimizer
	(registerizer) and generates good code (although <code>gccgo</code>
	can do noticeably better sometimes).
</dd>
<dt>
	<code>386</code> (a.k.a. <code>x86</code> or <code>x86-32</code>); <code>8g,8l,8c,8a</code>
</dt>
<dd>
	Comparable to the <code>amd64</code> port.
</dd>
<dt>
	<code>arm</code> (a.k.a. <code>ARM</code>); <code>5g,5l,5c,5a</code>
</dt>
<dd>
	Incomplete.
	It only supports Linux binaries, the optimizer is not enabled,
	and floating point is performed entirely in software.
	However, all tests pass.
	Work on the optimizer and use of the VFP hardware
	floating point unit is underway.
	Tested against a Nexus One.
</dd>
</dl>

<p>
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.
</p>

<p>
The compilers can target the FreeBSD, Linux, Native Client,
and OS X (a.k.a. Darwin) operating systems.
(A port to Microsoft Windows is in progress but incomplete.  See the 
<a href="http://code.google.com/p/go/wiki/WindowsPort">Windows Port</a>
page for details.)
The full set of supported combinations is listed in the discussion of
<a href="#environment">environment variables</a> below.
</p>

</div>

<h2 id="ctools">Install C tools, if needed</h2>

<p>The Go tool chain is written in C.
To build it, you need these programs installed: 
<ul>
<li>GCC, 
<li>the standard C libraries, 
<li>the parser generator Bison,
<li><tt>make</tt>, 
<li><tt>awk</tt>, and 
<li>the text editor <tt>ed</tt>.
</ul>
</p>

<p>On OS X, they can be
installed as part of
<a href="http://developer.apple.com/TOOLS/Xcode/">Xcode</a>. 
</p>

<p>On Ubuntu/Debian, use <code>sudo apt-get install bison ed gawk gcc libc6-dev make</code>.
</p>

<h2 id="mercurial">Install Mercurial, if needed</h2>

<p>
To perform the next step you must have Mercurial installed. (Check that you  have an <code>hg</code> command.) This suffices to install Mercurial on most systems:
</p>
<pre>
sudo easy_install mercurial
</pre>
(On Ubuntu/Debian, you might try <code>apt-get install python-setuptools
python-dev build-essential</code> first. The Mercurial in your distribution's
package repository will most likely be old and broken.)
</p>
<p>
If that fails, try installing manually from the <a href="http://mercurial.selenic.com/wiki/Download">Mercurial Download</a> page.</p>
</p>

<h2 id="fetch">Fetch the repository</h2>

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

<pre>
$ hg clone -r release https://go.googlecode.com/hg/ go
</pre>

<h2 id="install">Install Go</h2>

<p>
To build the Go distribution, run
</p>

<pre>
$ cd go/src
$ ./all.bash
</pre>

<p>
If all goes well, it will finish by printing output like:
</p>

<pre>
--- cd ../test
N known bugs; 0 unexpected bugs

---
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.
</pre>

<p>
where <var>N</var> is a number that varies from release to release
and the details on the last few lines will reflect the operating system,
architecture, and root directory used during the install.
</p>

<div class="detail">

<p>For more information about ways to control the build,
see the discussion of <a href="#environment">environment variables</a> below.</p>
</div>

<h2 id="writing">Writing programs</h2>

<p>
Given a file <code>file.go</code>, compile it using
</p>

<pre>
$ 6g file.go
</pre>

<p>
<code>6g</code> is the Go compiler for <code>amd64</code>; it will write the output
in <code>file.6</code>. The &lsquo;<code>6</code>&rsquo; identifies
files for the <code>amd64</code> architecture.
The identifier letters for <code>386</code> and <code>arm</code>
are &lsquo;<code>8</code>&rsquo; and &lsquo;<code>5</code>&rsquo;.
That is, if you were compiling for <code>386</code>, you would use
<code>8g</code> and the output would be named <code>file.8</code>.
</p>

<p>
To link the file, use
</p>

<pre>
$ 6l file.6
</pre>

<p>
and to run it
</p>

<pre>
$ ./6.out
</pre>

<p>A complete example:
</p>

<pre>
$ cat &gt;hello.go &lt;&lt;EOF
package main

import "fmt"

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

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

<div class="detail">
<p>
To build more complicated programs, you will probably
want to use a
<code>Makefile</code>.
There are examples in places like
<code>go/src/cmd/godoc/Makefile</code>
and <code>go/src/pkg/*/Makefile</code>.
The
<a href="contribute.html">document</a>
about contributing to the Go project
gives more detail about
the process of building and testing Go programs.
</p>
</div>

<h2 id="next">What's next</h2>

<p>
Start by reading the <a href="go_tutorial.html">Go Tutorial</a>.
</p>

<p>
Build a web application by following the <a href="codelab/wiki/">Wiki
Codelab</a>.
</p>

<p>
Read <a href="effective_go.html">Effective Go</a> to learn about writing
idiomatic Go code.
</p>

<p>
For the full story, consult Go's extensive 
<a href="docs.html">documentation</a>.
</p>

<h2 id="releases">Keeping up with releases</h2>

<p>New releases are announced on the <a href="http://groups.google.com/group/golang-nuts">Go Nuts</a> mailing list.
To update an existing tree to the latest release, you can run:
</p>

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

<h2 id="community">Community resources</h2>

<p>
For real-time help, there may be users or developers on
<code>#go-nuts</code> on the <a href="http://freenode.net/">Freenode</a> IRC server.
</p>

<p>
The official mailing list for discussion of the Go language is
<a href="http://groups.google.com/group/golang-nuts">Go Nuts</a>.
</p>

<p>
Bugs can be reported using the <a href="http://code.google.com/p/go/issues/list">Go issue tracker</a>.
</p>

<p>
For those who wish to keep up with development,
there is another mailing list, <a href="http://groups.google.com/group/golang-checkins">golang-checkins</a>,
that receives a message summarizing each checkin to the Go repository.
</p>

<h2 id="environment">Environment variables</h2>

<p>
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.
</p>

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

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

<dt>
<code>$GOOS</code> and <code>$GOARCH</code>
</dt>
<dd>
	The name of the target operating system and compilation architecture.
	These default to the values of <code>$GOHOSTOS</code> and
	<code>$GOHOSTARCH</code> respectively (described below).

	<p>
	Choices for <code>$GOOS</code> are <code>linux</code>,
	<code>freebsd</code>,
	<code>darwin</code> (Mac OS X 10.5 or 10.6),
	and <code>nacl</code> (Native Client, an incomplete port).
	Choices for <code>$GOARCH</code> are <code>amd64</code> (64-bit x86, the most mature port),
	<code>386</code> (32-bit x86), and
	<code>arm</code> (32-bit ARM, an incomplete port).
	The valid combinations of <code>$GOOS</code> and <code>$GOARCH</code> are:
	<table cellpadding="0">
	<tr>
	<th width="50"><th align="left" width="100"><code>$GOOS</code></th> <th align="left" width="100"><code>$GOARCH</code></th> <th align="left"></th>
	</tr>
	<tr>
	<td></td><td><code>darwin</code></td> <td><code>386</code></td>
	</tr>
	<tr>
	<td></td><td><code>darwin</code></td> <td><code>amd64</code></td>
	</tr>
	<tr>
	<td></td><td><code>freebsd</code></td> <td><code>386</code></td>
	</tr>
	<tr>
	<td></td><td><code>freebsd</code></td> <td><code>amd64</code></td>
	</tr>
	<tr>
	<td></td><td><code>linux</code></td> <td><code>386</code></td>
	</tr>
	<tr>
	<td></td><td><code>linux</code></td> <td><code>amd64</code></td>
	</tr>
	<tr>
	<td></td><td><code>linux</code></td> <td><code>arm</code></td> <td><i>incomplete</i></td>
	</tr>
	<tr>
	<td></td><td><code>nacl</code></td> <td><code>386</code></td>
	</tr>
	<tr>
	<td></td><td><code>windows</code></td> <td><code>386</code></td> <td><i>incomplete</i></td>
	</tr>
	</table>
</dd>

<dt>
<code>$GOHOSTOS</code> and <code>$GOHOSTARCH</code>
</dt>
<dd>
	The name of the host operating system and compilation architecture.
	These default to the local system's operating system and
	architecture.

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

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

<dt>
<code>$GOARM</code> (arm, default=6)
</dt>
<dd>
	The ARM architecture version the runtime libraries should target.
	ARMv6 cores have more efficient synchronization primitives. Setting
	<code>$GOARM</code> 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.
</dd>
</dl>

<p>
Note that <code>$GOARCH</code> and <code>$GOOS</code> identify the
<em>target</em> 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 <code>GOARCH</code> to <code>386</code>,
not <code>amd64</code>.
</p>

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

<pre>
export GOROOT=$HOME/go
export GOARCH=386
export GOOS=linux
</pre>