<!-- Installing Go -->

<h2>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>

<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>

<h2>Environment variables</h2>

<p>
The Go compilation environment depends on three environment variables plus one optional variable:
</p>

<dl>
<dt>
	<code>$GOROOT</code>
</dt>
<dd>The root of the Go tree.  Typically this is <code>$HOME/go</code>
	but it can be any directory.
</dd>

<dt>
<code>$GOOS</code> and <code>$GOARCH</code>
</dt>
<dd>
	The name of the target operating system and compilation architecture.
	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:
	<p>
	<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>
	</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>
	</tr>
	<tr>
	<td></td><td><code>nacl</code></td> <td><code>386</code></td>
	</tr>
	</table>
	<p>
</dd>

<dt>
<code>$GOBIN</code> (optional)
</dt>
<dd>
	The location where binaries will be installed.
	The default is <code>$HOME/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>$GOARM</code> (optional, arm, default=6)
</dt>
<dd>
	The ARM architecture version the runtime libraries should target.
	ARMv6 cores have more efficient synchronization primitives. Setting
	<code>$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.
</p>

<p>
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=amd64
export GOOS=linux
</pre>

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

<pre>
$ env | grep '^GO'
</pre>

<h2>Ports</h2>

<p>
Go compilers support two operating systems (Linux, Mac OS X) and
three instruction sets.
The versions for Linux and Mac are equally capable except that the ARM port
does not run on OS X (yet).
</p>
<p>
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. Not as well soaked but
	should be nearly as solid.

</dd>
<dt>
	<code>arm</code> (a.k.a. <code>ARM</code>); <code>5g,5l,5c,5a</code>
</dt>
<dd>
	It's got a couple of outstanding bugs but is improving. Tested against QEMU
	and an android phone.
</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>
See the separate <a href="gccgo_install.html"><code>gccgo</code> document</a>
for details about that compiler and environment.
</p>

<h2>Install C tools, if needed</h2>

<p>The Go tool chain is written in C.  To build it, you need
to have GCC, the standard C libraries, the parser generator Bison,
<tt>make</tt>, <tt>awk</tt>, and the text editor <tt>ed</tt> installed.  On OS X, they can be
installed as part of
<a href="http://developer.apple.com/TOOLS/Xcode/">Xcode</a>.  On Linux, use
</p>

<pre>
$ sudo apt-get install bison gcc libc6-dev ed gawk make
</pre>

<p>
(or the equivalent on your Linux distribution).
</p>

<h2>Fetch the repository</h2>

<p>
If you do not have Mercurial installed (you do not have an <code>hg</code> command),
this command:
</p>

<pre>
$ sudo easy_install mercurial
</pre>

<p>works on most systems.
(On Ubuntu/Debian, you might try <code>apt-get install python-setuptools python-dev build-essential gcc</code> first.)
If that fails, visit the <a href="http://mercurial.selenic.com/wiki/Download">Mercurial Download</a> page.</p>

<p>Make sure the <code>$GOROOT</code> directory does not exist or is empty.
Then check out the repository:</p>

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

<h2>Install Go</h2>

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

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

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

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

<p>
where <var>N</var> is a number that varies from release to release.
</p>

<h2>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>

<p>
To build more complicated programs, you will probably
want to use a
<code>Makefile</code>.
There are examples in places like
<code>$GOROOT/src/cmd/godoc/Makefile</code>
and <code>$GOROOT/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>

<h2>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 $GOROOT/src
$ hg pull
$ hg update release
$ ./all.bash
</pre>

<h2>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>