Golang环境配置及工程管理

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Install Golang

Golang安装参考https://golang.org/doc/install

相关环境变量

环境变量设置，将如下设置写到~/.profile文件中：

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export GOROOT=/usr/local/go
export GOBIN=$GOROOT/bin
export GOPATH=$HOME/go
export PATH=$PATH:$GOPATH:$GOBIN

GOROOT

GOROOT是go的安装路径
package runtime中：
/src/runtime/extern.go:213

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210	// GOROOT returns the root of the Go tree.
211	// It uses the GOROOT environment variable, if set,
212	// or else the root used during the Go build.
213	func GOROOT() string {
214		s := gogetenv("GOROOT")
215		if s != "" {
216			return s
217		}
218		return sys.DefaultGoroot
219	}

GOPATH

GOPATH是go的工作目录
package build中：
/src/go/build/build.go:204

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203	// gopath returns the list of Go path directories.
204	func (ctxt *Context) gopath() []string {
205		var all []string
206		for _, p := range ctxt.splitPathList(ctxt.GOPATH) {
207			if p == "" || p == ctxt.GOROOT {
208				// Empty paths are uninteresting.
209				// If the path is the GOROOT, ignore it.
210				// People sometimes set GOPATH=$GOROOT.
211				// Do not get confused by this common mistake.
212				continue
213			}
214			if strings.HasPrefix(p, "~") {
215				// Path segments starting with ~ on Unix are almost always
216				// users who have incorrectly quoted ~ while setting GOPATH,
217				// preventing it from expanding to $HOME.
218				// The situation is made more confusing by the fact that
219				// bash allows quoted ~ in $PATH (most shells do not).
220				// Do not get confused by this, and do not try to use the path.
221				// It does not exist, and printing errors about it confuses
222				// those users even more, because they think "sure ~ exists!".
223				// The go command diagnoses this situation and prints a
224				// useful error.
225				// On Windows, ~ is used in short names, such as c:\progra~1
226				// for c:\program files.
227				continue
228			}
229			all = append(all, p)
230		}
231		return all
232	}

GOBIN

GOBIN指向go安装目录中bin的位置
package main中：
/src/cmd/go/build.go:742

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740	var (
741		goroot    = filepath.Clean(runtime.GOROOT())
742		gobin     = os.Getenv("GOBIN")
743		gorootBin = filepath.Join(goroot, "bin")
744		gorootPkg = filepath.Join(goroot, "pkg")
745		gorootSrc = filepath.Join(goroot, "src")
746	)

扩展：go env

go env可查看更多的环境变量。

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$go env
GOARCH="amd64"                  # 编译之后可执行程序的CPU体系架构
GOBIN="/usr/local/go/bin"
GOEXE=""                        # ？
GOHOSTARCH="amd64"              # 主题CPU体系架构
GOHOSTOS="linux"                # 主机操作系统
GOOS="linux"                    # GO程序的运行的操作系统
GOPATH=""
GORACE=""                       # 应该是跟race有关？
GOROOT="/usr/local/go"
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"          # tool路径，比如cgo, compile, etc.
GO15VENDOREXPERIMENT="1"                                # 即将废除的东西
CC="gcc"                                                # C编译器, default是gcc, 也支持clang
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0"     # 编译参数
CXX="g++"                                               # C++编译器，default是g++，也支持clang++
CGO_ENABLED="1"                                         # 在build过程中控制cgo的用法

GO15VENDOREXPERIMENT
package main
/src/cmd/go/pkg.go:273

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266	// The Go 1.5 vendoring experiment was enabled by setting GO15VENDOREXPERIMENT=1.
267	// In Go 1.6 this is on by default and is disabled by setting GO15VENDOREXPERIMENT=0.
268	// In Go 1.7 the variable will stop having any effect.
269	// The variable is obnoxiously long so that years from now when people find it in
270	// their profiles and wonder what it does, there is some chance that a web search
271	// might answer the question.
272	// There is a copy of this variable in src/go/build/build.go. Delete that one when this one goes away.
273	var go15VendorExperiment = os.Getenv("GO15VENDOREXPERIMENT") != "0"

编译运行

hello.go

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package main
import "fmt"
func main() {
    fmt.Println("Hello, World");
}

Refer to “Go Playground” https://play.golang.org/p/F8Ev-6husG

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go run hello.go

go run是集编译，链接，运行于一体。运行完之后在当前目录下看不到任何中间文件和最终的可执行文件

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go build hello.go
./hello

go build是编译，链接。执行完之后可以在当前目录下看见可执行程序hello. 使用-work参数可以生成临时文件。

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file /tmp/go-build373605995/command-line-arguments.a
/tmp/go-build373605995/command-line-arguments.a: current ar archive

工程管理

Go工程目录树结构

Go管理Project的方法比较特别，没有工程文件，而是使用目录结构和包名来推导工程结构和构建顺序，所以Go工程的目录结构和包名就很讲究，必须符合规定。
以一个加减乘除计算器为例。
目录结构如下：

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.
└── littlecalc
    ├── bin
    │   └── calc
    ├── pkg
    └── src
        ├── calc
        │   └── calc.go
        └── littlemath
            ├── add.go
            ├── div.go
            ├── mul.go
            └── sub.go

一般Go工程都会包含bin, pkg, src 3个目录。bin和pkg可以先不创建，go命令可以自动创建（比如 go install）。
src目录顾名思义，是源码文件，Go源文件以package方式组织，新建一个package，就是在src下新建一个文件夹。

如上面tree所示，src下有calc和littlemath 2个文件夹，即有2个package，一个littlemath package, littlemath下的4支文件中的package名称最好和目录名称保持一致，如果不一致就会比较麻烦，容易让人产生混淆，后面会说明package名称和目录名称不一致的情形。

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package littlemath

另一个calc文件夹，是main package，calc.go中有表明是main package.

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package main

构建工程

构建之前需要设置此工程的GOPATH. 每个工程都需要设置GOPATH环境变量，感觉还是有点小麻烦的。编辑~/.profile，将littlecalc路径添加到GOPATH中，然后source ~/.profile.

使用go build来构建工程

执行如下操作即可在bin目录下看到生成的可执行文件calc.

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cd bin
go build -x calc

使用-x参数查看build中间过程。

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WORK=/tmp/go-build782666460
mkdir -p $WORK/littlemath/_obj/
mkdir -p $WORK/
cd /home/joe/go/littlecalc/src/littlemath
/usr/local/go/pkg/tool/linux_amd64/compile -o $WORK/littlemath.a -trimpath $WORK -p littlemath -complete -buildid 3e05bdb1a540f52eb8c3fea594081c07afc21a07 -D _/home/joe/go/littlecalc/src/littlemath -I $WORK -pack ./add.go ./div.go ./mul.go ./sub.go
mkdir -p $WORK/calc/_obj/
mkdir -p $WORK/calc/_obj/exe/
cd /home/joe/go/littlecalc/src/calc
/usr/local/go/pkg/tool/linux_amd64/compile -o $WORK/calc.a -trimpath $WORK -p main -complete -buildid 87c3fe780b981105ecb696b77b4ab0998e93526b -D _/home/joe/go/littlecalc/src/calc -I $WORK -I /home/joe/go/littlecalc/pkg/linux_amd64 -pack ./calc.go
cd .
/usr/local/go/pkg/tool/linux_amd64/link -o $WORK/calc/_obj/exe/a.out -L $WORK -L /home/joe/go/littlecalc/pkg/linux_amd64 -extld=gcc -buildmode=exe -buildid=87c3fe780b981105ecb696b77b4ab0998e93526b $WORK/calc.a
mv $WORK/calc/_obj/exe/a.out calc

先会创建临时目录才存放build中间结果，真正进行编译的是compile命令，链接的是link命令。最终build的可执行文件从临时目录中移到当前工作目录下。

执行完go build的目录结构如下。

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.
├── bin
│   └── calc
├── pkg
└── src
    ├── calc
    │   └── calc.go
    └── littlemath
        ├── add.go
        ├── div.go
        ├── mul.go
        └── sub.go

使用go install来构建工程

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go install -x calc

得到的结果如下。

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WORK=/tmp/go-build478301029
mkdir -p $WORK/littlemath/_obj/
mkdir -p $WORK/
cd /home/joe/go/littlecalc/src/littlemath
/usr/local/go/pkg/tool/linux_amd64/compile -o $WORK/littlemath.a -trimpath $WORK -p littlemath -complete -buildid 3e05bdb1a540f52eb8c3fea594081c07afc21a07 -D _/home/joe/go/littlecalc/src/littlemath -I $WORK -pack ./add.go ./div.go ./mul.go ./sub.go
    mkdir -p /home/joe/go/littlecalc/pkg/linux_amd64/
mv $WORK/littlemath.a /home/joe/go/littlecalc/pkg/linux_amd64/littlemath.a
mkdir -p $WORK/calc/_obj/
mkdir -p $WORK/calc/_obj/exe/
cd /home/joe/go/littlecalc/src/calc
/usr/local/go/pkg/tool/linux_amd64/compile -o $WORK/calc.a -trimpath $WORK -p main -complete -buildid 87c3fe780b981105ecb696b77b4ab0998e93526b -D _/home/joe/go/littlecalc/src/calc -I $WORK -I /home/joe/go/littlecalc/pkg/linux_amd64 -pack ./calc.go
cd .
/usr/local/go/pkg/tool/linux_amd64/link -o $WORK/calc/_obj/exe/a.out -L $WORK -L /home/joe/go/littlecalc/pkg/linux_amd64 -extld=gcc -buildmode=exe -buildid=87c3fe780b981105ecb696b77b4ab0998e93526b $WORK/calc.a
mkdir -p /usr/local/go/bin/
cp $WORK/calc/_obj/exe/a.out /usr/local/go/bin/calc
go install calc: open /usr/local/go/bin/calc: permission denied

发现最终生成的结果想要拷贝到/usr/local/go/bin下，因为当前时非root用户，没有权限执行此操作。奇怪的是，为什么不是往当前工作目录的bin下拷贝呢？原来是$GOBIN环境变量导致的。前面将$GOBIN设置成了$GOROOT/bin, 重新设置环境变量如下。

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export GOROOT=/usr/local/go
export GOBIN=
export GOPATH=$HOME/go/littlecalc
export PATH=$PATH:$GOPATH:$GOROOT/bin

然后再执行go install calc，可以看到目录树如下。在bin下多了一个叫calc的最终可执行文件；在pkg下多了一个package文件littlemath.a.

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.
├── bin
│   └── calc
├── pkg
│   └── linux_amd64
│       └── littlemath.a
└── src
    ├── calc
    │   └── calc.go
    └── littlemath
        ├── add.go
        ├── div.go
        ├── mul.go
        └── sub.go

go build和go install的区别

其实从上述-x参数得到的结果也可以粗略看出二者的区别。
go install会创建bin和pkg，会将编译出所依赖的package放在pkg中，将最终的可执行文件放在bin中，这个bin的具体位置受到$GOBIN环境变量的影响。

package名称与目录名称不一致的情形

对上面小工程的目录树结构稍作改变，将littlemath改名成mymath.

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.
└── src
    ├── calc
    │   └── calc.go
    └── mymath
        ├── add.go
        ├── div.go
        ├── mul.go
        └── sub.go

mymath中的源文件中package名字仍然保留littlemath.

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package littlemath

calc/calc.goimport的package也保留littlemath.

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import "littlemath"

然后go install -x calc会提示找不到littlemath package.

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src/calc/calc.go:5:8: cannot find package "littlemath" in any of:
	/usr/local/go/src/littlemath (from $GOROOT)
	/home/joe/go/littlecalc/src/littlemath (from $GOPATH)

但将calc/calc.go中import的package改成mymath，则可编译成功。

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import "mymath"

go install -x calc

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WORK=/tmp/go-build875817729
mkdir -p $WORK/mymath/_obj/
mkdir -p $WORK/
cd /home/joe/go/littlecalc/src/mymath
/usr/local/go/pkg/tool/linux_amd64/compile -o $WORK/mymath.a -trimpath $WORK -p mymath -complete -buildid 3e05bdb1a540f52eb8c3fea594081c07afc21a07 -D _/home/joe/go/littlecalc/src/mymath -I $WORK -pack ./add.go ./div.go ./mul.go ./sub.go
mkdir -p /home/joe/go/littlecalc/pkg/linux_amd64/
mv $WORK/mymath.a /home/joe/go/littlecalc/pkg/linux_amd64/mymath.a
mkdir -p $WORK/calc/_obj/
mkdir -p $WORK/calc/_obj/exe/
cd /home/joe/go/littlecalc/src/calc
/usr/local/go/pkg/tool/linux_amd64/compile -o $WORK/calc.a -trimpath $WORK -p main -complete -buildid b26a0e0d54c06e74fff3641e2e7c712ad9527d73 -D _/home/joe/go/littlecalc/src/calc -I $WORK -I /home/joe/go/littlecalc/pkg/linux_amd64 -pack ./calc.go
cd .
/usr/local/go/pkg/tool/linux_amd64/link -o $WORK/calc/_obj/exe/a.out -L $WORK -L /home/joe/go/littlecalc/pkg/linux_amd64 -extld=gcc -buildmode=exe -buildid=b26a0e0d54c06e74fff3641e2e7c712ad9527d73 $WORK/calc.a
mkdir -p /home/joe/go/littlecalc/bin/
mv $WORK/calc/_obj/exe/a.out /home/joe/go/littlecalc/bin/calc

以上可以发现，编译产生的静态包(package)文件是以目录名来命名的。import时应该是目录名，而在引用包时则需要包名。
虽然将littlemath改成了mymath，calc/calc.go中的import "littlemath"改成了import "mymath"，
但是mymath下的源文件中仍然定义的是package littlemath，
calc/calc.go中引用包中的函数仍然是类似于little.Add()这样的。

摆脱每新建一个工程就需要重新设置GOPATH的方法

来自于Go项目的目录结构。
与src平行路径新建一支build.sh文件，内容如下。

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#!/usr/bin/env bash
pkg=$1
CURDIR=`pwd`
OLDGOPATH="$GOPATH"
export GOPATH="$CURDIR"
gofmt -w src
go install -x $1
export GOPATH="$OLDGOPATH"
echo 'finished'

使用方法：sh build.sh [packages]，如sh build.sh calc.

Appendix

calc源码:
https://github.com/magicse7en/go-practice/commit/668cd75c498bfd1c8542eeefb8547c53dd2e7cde
修改包名与目录名不一致的源码:
https://github.com/magicse7en/go-practice/commit/fce999305dd0c025493a4e3282379291c8d8f69e
build.sh

Reference

Go项目的目录结构