mirror of
https://github.com/golang/go
synced 2024-11-08 18:46:16 -07:00
b6c871a2af
We were not being consistent. Standardize on toolchain. Change-Id: Id0e756b5214ce4a1341f733634ed95263f03a61c Reviewed-on: https://go-review.googlesource.com/87017 Run-TryBot: Russ Cox <rsc@golang.org> Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org> Reviewed-by: Ian Lance Taylor <iant@golang.org>
255 lines
11 KiB
HTML
255 lines
11 KiB
HTML
<!--{
|
|
"title": "About the go command"
|
|
}-->
|
|
|
|
<p>The Go distribution includes a command, named
|
|
"<code><a href="/cmd/go/">go</a></code>", that
|
|
automates the downloading, building, installation, and testing of Go packages
|
|
and commands. This document talks about why we wrote a new command, what it
|
|
is, what it's not, and how to use it.</p>
|
|
|
|
<h2>Motivation</h2>
|
|
|
|
<p>You might have seen early Go talks in which Rob Pike jokes that the idea
|
|
for Go arose while waiting for a large Google server to compile. That
|
|
really was the motivation for Go: to build a language that worked well
|
|
for building the large software that Google writes and runs. It was
|
|
clear from the start that such a language must provide a way to
|
|
express dependencies between code libraries clearly, hence the package
|
|
grouping and the explicit import blocks. It was also clear from the
|
|
start that you might want arbitrary syntax for describing the code
|
|
being imported; this is why import paths are string literals.</p>
|
|
|
|
<p>An explicit goal for Go from the beginning was to be able to build Go
|
|
code using only the information found in the source itself, not
|
|
needing to write a makefile or one of the many modern replacements for
|
|
makefiles. If Go needed a configuration file to explain how to build
|
|
your program, then Go would have failed.</p>
|
|
|
|
<p>At first, there was no Go compiler, and the initial development
|
|
focused on building one and then building libraries for it. For
|
|
expedience, we postponed the automation of building Go code by using
|
|
make and writing makefiles. When compiling a single package involved
|
|
multiple invocations of the Go compiler, we even used a program to
|
|
write the makefiles for us. You can find it if you dig through the
|
|
repository history.</p>
|
|
|
|
<p>The purpose of the new go command is our return to this ideal, that Go
|
|
programs should compile without configuration or additional effort on
|
|
the part of the developer beyond writing the necessary import
|
|
statements.</p>
|
|
|
|
<h2>Configuration versus convention</h2>
|
|
|
|
<p>The way to achieve the simplicity of a configuration-free system is to
|
|
establish conventions. The system works only to the extent that those conventions
|
|
are followed. When we first launched Go, many people published packages that
|
|
had to be installed in certain places, under certain names, using certain build
|
|
tools, in order to be used. That's understandable: that's the way it works in
|
|
most other languages. Over the last few years we consistently reminded people
|
|
about the <code>goinstall</code> command
|
|
(now replaced by <a href="/cmd/go/#hdr-Download_and_install_packages_and_dependencies"><code>go get</code></a>)
|
|
and its conventions: first, that the import path is derived in a known way from
|
|
the URL of the source code; second, that the place to store the sources in
|
|
the local file system is derived in a known way from the import path; third,
|
|
that each directory in a source tree corresponds to a single package; and
|
|
fourth, that the package is built using only information in the source code.
|
|
Today, the vast majority of packages follow these conventions.
|
|
The Go ecosystem is simpler and more powerful as a result.</p>
|
|
|
|
<p>We received many requests to allow a makefile in a package directory to
|
|
provide just a little extra configuration beyond what's in the source code.
|
|
But that would have introduced new rules. Because we did not accede to such
|
|
requests, we were able to write the go command and eliminate our use of make
|
|
or any other build system.</p>
|
|
|
|
<p>It is important to understand that the go command is not a general
|
|
build tool. It cannot be configured and it does not attempt to build
|
|
anything but Go packages. These are important simplifying
|
|
assumptions: they simplify not only the implementation but also, more
|
|
important, the use of the tool itself.</p>
|
|
|
|
<h2>Go's conventions</h2>
|
|
|
|
<p>The <code>go</code> command requires that code adheres to a few key,
|
|
well-established conventions.</p>
|
|
|
|
<p>First, the import path is derived in an known way from the URL of the
|
|
source code. For Bitbucket, GitHub, Google Code, and Launchpad, the
|
|
root directory of the repository is identified by the repository's
|
|
main URL, without the <code>http://</code> prefix. Subdirectories are named by
|
|
adding to that path.
|
|
For example, the Go example programs are obtained by running</p>
|
|
|
|
<pre>
|
|
git clone https://github.com/golang/example
|
|
</pre>
|
|
|
|
<p>and thus the import path for the root directory of that repository is
|
|
"<code>github.com/golang/example</code>".
|
|
The <a href="https://godoc.org/github.com/golang/example/stringutil">stringutil</a>
|
|
package is stored in a subdirectory, so its import path is
|
|
"<code>github.com/golang/example/stringutil</code>".</p>
|
|
|
|
<p>These paths are on the long side, but in exchange we get an
|
|
automatically managed name space for import paths and the ability for
|
|
a tool like the go command to look at an unfamiliar import path and
|
|
deduce where to obtain the source code.</p>
|
|
|
|
<p>Second, the place to store sources in the local file system is derived
|
|
in a known way from the import path, specifically
|
|
<code>$GOPATH/src/<import-path></code>.
|
|
If unset, <code>$GOPATH</code> defaults to a subdirectory
|
|
named <code>go</code> in the user's home directory.
|
|
If <code>$GOPATH</code> is set to a list of paths, the go command tries
|
|
<code><dir>/src/<import-path></code> for each of the directories in
|
|
that list.
|
|
</p>
|
|
|
|
<p>Each of those trees contains, by convention, a top-level directory named
|
|
"<code>bin</code>", for holding compiled executables, and a top-level directory
|
|
named "<code>pkg</code>", for holding compiled packages that can be imported,
|
|
and the "<code>src</code>" directory, for holding package source files.
|
|
Imposing this structure lets us keep each of these directory trees
|
|
self-contained: the compiled form and the sources are always near each
|
|
other.</p>
|
|
|
|
<p>These naming conventions also let us work in the reverse direction,
|
|
from a directory name to its import path. This mapping is important
|
|
for many of the go command's subcommands, as we'll see below.</p>
|
|
|
|
<p>Third, each directory in a source tree corresponds to a single
|
|
package. By restricting a directory to a single package, we don't have
|
|
to create hybrid import paths that specify first the directory and
|
|
then the package within that directory. Also, most file management
|
|
tools and UIs work on directories as fundamental units. Tying the
|
|
fundamental Go unit—the package—to file system structure means
|
|
that file system tools become Go package tools. Copying, moving, or
|
|
deleting a package corresponds to copying, moving, or deleting a
|
|
directory.</p>
|
|
|
|
<p>Fourth, each package is built using only the information present in
|
|
the source files. This makes it much more likely that the tool will
|
|
be able to adapt to changing build environments and conditions. For
|
|
example, if we allowed extra configuration such as compiler flags or
|
|
command line recipes, then that configuration would need to be updated
|
|
each time the build tools changed; it would also be inherently tied
|
|
to the use of a specific toolchain.</p>
|
|
|
|
<h2>Getting started with the go command</h2>
|
|
|
|
<p>Finally, a quick tour of how to use the go command.
|
|
As mentioned above, the default <code>$GOPATH</code> on Unix is <code>$HOME/go</code>.
|
|
We'll store our programs there.
|
|
To use a different location, you can set <code>$GOPATH</code>;
|
|
see <a href="/doc/code.html">How to Write Go Code</a> for details.
|
|
|
|
<p>We first add some source code. Suppose we want to use
|
|
the indexing library from the codesearch project along with a left-leaning
|
|
red-black tree. We can install both with the "<code>go get</code>"
|
|
subcommand:</p>
|
|
|
|
<pre>
|
|
$ go get github.com/google/codesearch/index
|
|
$ go get github.com/petar/GoLLRB/llrb
|
|
$
|
|
</pre>
|
|
|
|
<p>Both of these projects are now downloaded and installed into <code>$HOME/go</code>,
|
|
which contains the two directories
|
|
<code>src/github.com/google/codesearch/index/</code> and
|
|
<code>src/github.com/petar/GoLLRB/llrb/</code>, along with the compiled
|
|
packages (in <code>pkg/</code>) for those libraries and their dependencies.</p>
|
|
|
|
<p>Because we used version control systems (Mercurial and Git) to check
|
|
out the sources, the source tree also contains the other files in the
|
|
corresponding repositories, such as related packages. The "<code>go list</code>"
|
|
subcommand lists the import paths corresponding to its arguments, and
|
|
the pattern "<code>./...</code>" means start in the current directory
|
|
("<code>./</code>") and find all packages below that directory
|
|
("<code>...</code>"):</p>
|
|
|
|
<pre>
|
|
$ cd $HOME/go/src
|
|
$ go list ./...
|
|
github.com/google/codesearch/cmd/cgrep
|
|
github.com/google/codesearch/cmd/cindex
|
|
github.com/google/codesearch/cmd/csearch
|
|
github.com/google/codesearch/index
|
|
github.com/google/codesearch/regexp
|
|
github.com/google/codesearch/sparse
|
|
github.com/petar/GoLLRB/example
|
|
github.com/petar/GoLLRB/llrb
|
|
$
|
|
</pre>
|
|
|
|
<p>We can also test those packages:</p>
|
|
|
|
<pre>
|
|
$ go test ./...
|
|
? github.com/google/codesearch/cmd/cgrep [no test files]
|
|
? github.com/google/codesearch/cmd/cindex [no test files]
|
|
? github.com/google/codesearch/cmd/csearch [no test files]
|
|
ok github.com/google/codesearch/index 0.203s
|
|
ok github.com/google/codesearch/regexp 0.017s
|
|
? github.com/google/codesearch/sparse [no test files]
|
|
? github.com/petar/GoLLRB/example [no test files]
|
|
ok github.com/petar/GoLLRB/llrb 0.231s
|
|
$
|
|
</pre>
|
|
|
|
<p>If a go subcommand is invoked with no paths listed, it operates on the
|
|
current directory:</p>
|
|
|
|
<pre>
|
|
$ cd github.com/google/codesearch/regexp
|
|
$ go list
|
|
github.com/google/codesearch/regexp
|
|
$ go test -v
|
|
=== RUN TestNstateEnc
|
|
--- PASS: TestNstateEnc (0.00s)
|
|
=== RUN TestMatch
|
|
--- PASS: TestMatch (0.00s)
|
|
=== RUN TestGrep
|
|
--- PASS: TestGrep (0.00s)
|
|
PASS
|
|
ok github.com/google/codesearch/regexp 0.018s
|
|
$ go install
|
|
$
|
|
</pre>
|
|
|
|
<p>That "<code>go install</code>" subcommand installs the latest copy of the
|
|
package into the pkg directory. Because the go command can analyze the
|
|
dependency graph, "<code>go install</code>" also installs any packages that
|
|
this package imports but that are out of date, recursively.</p>
|
|
|
|
<p>Notice that "<code>go install</code>" was able to determine the name of the
|
|
import path for the package in the current directory, because of the convention
|
|
for directory naming. It would be a little more convenient if we could pick
|
|
the name of the directory where we kept source code, and we probably wouldn't
|
|
pick such a long name, but that ability would require additional configuration
|
|
and complexity in the tool. Typing an extra directory name or two is a small
|
|
price to pay for the increased simplicity and power.</p>
|
|
|
|
<h2>Limitations</h2>
|
|
|
|
<p>As mentioned above, the go command is not a general-purpose build
|
|
tool.
|
|
In particular, it does not have any facility for generating Go
|
|
source files <em>during</em> a build, although it does provide
|
|
<a href="/cmd/go/#hdr-Generate_Go_files_by_processing_source"><code>go</code>
|
|
<code>generate</code></a>,
|
|
which can automate the creation of Go files <em>before</em> the build.
|
|
For more advanced build setups, you may need to write a
|
|
makefile (or a configuration file for the build tool of your choice)
|
|
to run whatever tool creates the Go files and then check those generated source files
|
|
into your repository. This is more work for you, the package author,
|
|
but it is significantly less work for your users, who can use
|
|
"<code>go get</code>" without needing to obtain and build
|
|
any additional tools.</p>
|
|
|
|
<h2>More information</h2>
|
|
|
|
<p>For more information, read <a href="/doc/code.html">How to Write Go Code</a>
|
|
and see the <a href="/cmd/go/">go command documentation</a>.</p>
|