Merging other languages
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James Miranda
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en/01.2.md
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# 1.2 GOPATH与工作空间
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前面我们在安装Go的时候看到需要设置GOPATH变量，Go从1.1版本开始必须设置这个变量，而且不能和Go的安装目录一样，这个目录用来存放Go源码，Go的可运行文件，以及相应的编译之后的包文件。所以这个目录下面有三个子目录：src、bin、pkg
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## GOPATH设置
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go 命令依赖一个重要的环境变量：$GOPATH
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Windows系统中环境变量的形式为`%GOPATH%`，本书主要使用Unix形式，Windows用户请自行替换。
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*（注：这个不是Go安装目录。下面以笔者的工作目录为示例，如果你想不一样请把GOPATH替换成你的工作目录。）*
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在类似 Unix 环境大概这样设置：
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```sh
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export GOPATH=/home/apple/mygo
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```
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为了方便，应该新建以上文件夹，并且上一行加入到 `.bashrc` 或者 `.zshrc` 或者自己的 `sh` 的配置文件中。
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Windows 设置如下，新建一个环境变量名称叫做GOPATH：
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```sh
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GOPATH=c:\mygo
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```
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GOPATH允许多个目录，当有多个目录时，请注意分隔符，多个目录的时候Windows是分号，Linux系统是冒号，当有多个GOPATH时，默认会将go get的内容放在第一个目录下。
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以上 $GOPATH 目录约定有三个子目录：
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- src 存放源代码（比如：.go .c .h .s等）
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- pkg 编译后生成的文件（比如：.a）
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- bin 编译后生成的可执行文件（为了方便，可以把此目录加入到 $PATH 变量中，如果有多个gopath，那么使用`${GOPATH//://bin:}/bin`添加所有的bin目录）
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以后我所有的例子都是以mygo作为我的gopath目录
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## 代码目录结构规划
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GOPATH下的src目录就是接下来开发程序的主要目录，所有的源码都是放在这个目录下面，那么一般我们的做法就是一个目录一个项目，例如: $GOPATH/src/mymath 表示mymath这个应用包或者可执行应用，这个根据package是main还是其他来决定，main的话就是可执行应用，其他的话就是应用包，这个会在后续详细介绍package。
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所以当新建应用或者一个代码包时都是在src目录下新建一个文件夹，文件夹名称一般是代码包名称，当然也允许多级目录，例如在src下面新建了目录$GOPATH/src/github.com/astaxie/beedb 那么这个包路径就是"github.com/astaxie/beedb"，包名称是最后一个目录beedb
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下面我就以mymath为例来讲述如何编写应用包，执行如下代码
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```sh
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cd $GOPATH/src
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mkdir mymath
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```
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新建文件sqrt.go，内容如下
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```go
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// $GOPATH/src/mymath/sqrt.go源码如下：
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package mymath
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func Sqrt(x float64) float64 {
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z := 0.0
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for i := 0; i < 1000; i++ {
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z -= (z*z - x) / (2 * x)
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}
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return z
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}
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```
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这样我的应用包目录和代码已经新建完毕，注意：一般建议package的名称和目录名保持一致
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## 编译应用
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上面我们已经建立了自己的应用包，如何进行编译安装呢？有两种方式可以进行安装
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1、只要进入对应的应用包目录，然后执行`go install`，就可以安装了
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2、在任意的目录执行如下代码`go install mymath`
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安装完之后，我们可以进入如下目录
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```sh
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cd $GOPATH/pkg/${GOOS}_${GOARCH}
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//可以看到如下文件
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mymath.a
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```
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这个.a文件是应用包，那么我们如何进行调用呢？
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接下来我们新建一个应用程序来调用这个应用包
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新建应用包mathapp
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```sh
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cd $GOPATH/src
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mkdir mathapp
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cd mathapp
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vim main.go
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```
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`$GOPATH/src/mathapp/main.go`源码：
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```go
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package main
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import (
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"mymath"
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"fmt"
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)
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func main() {
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fmt.Printf("Hello, world. Sqrt(2) = %v\n", mymath.Sqrt(2))
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}
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```
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可以看到这个的package是`main`，import里面调用的包是`mymath`,这个就是相对于`$GOPATH/src`的路径，如果是多级目录，就在import里面引入多级目录，如果你有多个GOPATH，也是一样，Go会自动在多个`$GOPATH/src`中寻找。
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如何编译程序呢？进入该应用目录，然后执行`go build`，那么在该目录下面会生成一个mathapp的可执行文件
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```sh
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./mathapp
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```
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输出如下内容
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```sh
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Hello, world. Sqrt(2) = 1.414213562373095
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```
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如何安装该应用，进入该目录执行`go install`,那么在$GOPATH/bin/下增加了一个可执行文件mathapp, 还记得前面我们把`$GOPATH/bin`加到我们的PATH里面了，这样可以在命令行输入如下命令就可以执行
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```sh
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mathapp
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```
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也是输出如下内容
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Hello, world. Sqrt(2) = 1.414213562373095
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这里我们展示如何编译和安装一个可运行的应用，以及如何设计我们的目录结构。
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## 获取远程包
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go语言有一个获取远程包的工具就是`go get`，目前go get支持多数开源社区(例如：github、googlecode、bitbucket、Launchpad)
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go get github.com/astaxie/beedb
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>go get -u 参数可以自动更新包，而且当go get的时候会自动获取该包依赖的其他第三方包
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通过这个命令可以获取相应的源码，对应的开源平台采用不同的源码控制工具，例如github采用git、googlecode采用hg，所以要想获取这些源码，必须先安装相应的源码控制工具
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通过上面获取的代码在我们本地的源码相应的代码结构如下
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$GOPATH
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src
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|--github.com
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|-astaxie
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|-beedb
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pkg
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|--相应平台
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|-github.com
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|--astaxie
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|beedb.a
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go get本质上可以理解为首先第一步是通过源码工具clone代码到src下面，然后执行`go install`
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在代码中如何使用远程包，很简单的就是和使用本地包一样，只要在开头import相应的路径就可以
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import "github.com/astaxie/beedb"
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## 程序的整体结构
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通过上面建立的我本地的mygo的目录结构如下所示
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bin/
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mathapp
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pkg/
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平台名/ 如：darwin_amd64、linux_amd64
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mymath.a
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github.com/
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astaxie/
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beedb.a
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src/
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mathapp
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main.go
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mymath/
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sqrt.go
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github.com/
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astaxie/
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beedb/
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beedb.go
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util.go
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从上面的结构我们可以很清晰的看到，bin目录下面存的是编译之后可执行的文件，pkg下面存放的是应用包，src下面保存的是应用源代码
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## links
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* [目录](<preface.md>)
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* 上一节: [GO安装](<01.1.md>)
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* 下一节: [GO 命令](<01.3.md>)
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#1.2 $GOPATH and workspace
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## $GOPATH
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Go commands all rely on one important environment variable called $GOPATH. Notice that this is not the $GOROOT variable where Go is installed. This variable points to the workspace of Go on your computer (I use this path on my computer; if you don't have the same directory structure, please replace by yourself).
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In Unix-like systems, the variable should be used like this:
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export GOPATH=/home/apple/mygo
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In Windows, you need to create a new environment variable called GOPATH, then set its value to `c:\mygo`( ***This value depends on where your workspace is located*** )
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It's OK to have more than one path (workspace) in $GOPATH, but remember that you have to use `:`(`;` in Windows) to break them up. At this point, `go get` will save the content to your first path in $GOPATH.
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In $GOPATH, you must have three folders as follows.
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- `src` for source files whose suffix is .go, .c, .g, .s.
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- `pkg` for compiled files whose suffix is .a.
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- `bin` for executable files
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In this book, I use `mygo` as my only path in $GOPATH.
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## Package directory
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Create package source files and folders like `$GOPATH/src/mymath/sqrt.go` (`mymath` is the package name) ( ***Author uses `mymath` as his package name, and same name for the folder where contains package source files***)
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Every time you create a package, you should create a new folder in the `src` directory. Folder names are usually the same as the package that you are going to use. You can have multi-level directories if you want to. For example, if you create the directory `$GOPATH/src/github.com/astaxie/beedb`, then the package path would be `github.com/astaxie/beedb`. The package name will be the last directory in your path, which is `beedb` in this case.
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Execute following commands. ( ***Now author goes back to talk examples*** )
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cd $GOPATH/src
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mkdir mymath
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Create a new file called `sqrt.go`, type following content to your file.
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// Source code of $GOPATH/src/mymath/sqrt.go
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package mymath
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func Sqrt(x float64) float64 {
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z := 0.0
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for i := 0; i < 1000; i++ {
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z -= (z*z - x) / (2 * x)
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}
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return z
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}
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Now my package directory has been created and its code has been written. I recommend that you use the same name for your packages as their corresponding directories, and that the directories contain all of the package source files.
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## Compile packages
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We've already created our package above, but how do we compile it for practical purposes? There are two ways to do this.
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1. Switch your work path to the directory of your package, then execute the `go install` command.
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2. Execute the above command except with a file name, like `go install mymath`.
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After compiling, we can open the following folder.
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cd $GOPATH/pkg/${GOOS}_${GOARCH}
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// you can see the file was generated
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mymath.a
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The file whose suffix is `.a` is the binary file of our package. How do we use it?
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Obviously, we need to create a new application to use it.
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Create a new application package called `mathapp`.
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cd $GOPATH/src
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mkdir mathapp
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cd mathapp
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vim main.go
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code
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//$GOPATH/src/mathapp/main.go source code.
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package main
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import (
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"mymath"
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"fmt"
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)
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func main() {
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fmt.Printf("Hello, world. Sqrt(2) = %v\n", mymath.Sqrt(2))
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}
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To compile this application, you need to switch to the application directory, which in this case is `$GOPATH/src/mathapp`, then execute the `go install` command. Now you should see an executable file called `mathapp` was generated in the directory `$GOPATH/bin/`. To run this program, use the `./mathapp` command. You should see the following content in your terminal.
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Hello world. Sqrt(2) = 1.414213562373095
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## Install remote packages
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Go has a tool for installing remote packages, which is a command called `go get`. It supports most open source communities, including Github, Google Code, BitBucket, and Launchpad.
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go get github.com/astaxie/beedb
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You can use `go get -u …` to update your remote packages and it will automatically install all the dependent packages as well.
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This tool will use different version control tools for different open source platforms. For example, `git` for Github and `hg` for Google Code. Therefore, you have to install these version control tools before you use `go get`.
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After executing the above commands, the directory structure should look like following.
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$GOPATH
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src
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|-github.com
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|-astaxie
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|-beedb
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pkg
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|--${GOOS}_${GOARCH}
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|-github.com
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|-astaxie
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|-beedb.a
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Actually, `go get` clones source code to the $GOPATH/src of the local file system, then executes `go install`.
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You can use remote packages in the same way that we use local packages.
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import "github.com/astaxie/beedb"
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## Directory complete structure
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If you've followed all of the above steps, your directory structure should now look like the following.
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bin/
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mathapp
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pkg/
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${GOOS}_${GOARCH}, such as darwin_amd64, linux_amd64
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mymath.a
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github.com/
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astaxie/
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beedb.a
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src/
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mathapp
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main.go
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mymath/
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sqrt.go
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github.com/
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astaxie/
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beedb/
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beedb.go
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util.go
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Now you are able to see the directory structure clearly; `bin` contains executable files, `pkg` contains compiled files and `src` contains package source files.
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(The format of environment variables in Windows is `%GOPATH%`, however this book mainly follows the Unix-style, so Windows users need to replace these yourself.)
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## Links
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- [Directory](preface.md)
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- Previous section: [Installation](01.1.md)
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- Next section: [Go commands](01.3.md)
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Reference in New Issue
Block a user