在golang里调用外部命令

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最近正在用go写一个各语言的lint server，需要调用外部的命令，所以这里整理一下用到的方法。

Command

在os/exec包中有一个 type 叫 cmd，定义如下：

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type Cmd struct {
        // Path is the path of the command to run.
        //
        // This is the only field that must be set to a non-zero
        // value. If Path is relative, it is evaluated relative
        // to Dir.
        Path string

        // Args holds command line arguments, including the command as Args[0].
        // If the Args field is empty or nil, Run uses {Path}.
        //
        // In typical use, both Path and Args are set by calling Command.
        Args []string

        // Env specifies the environment of the process.
        // If Env is nil, Run uses the current process's environment.
        Env []string

        // Dir specifies the working directory of the command.
        // If Dir is the empty string, Run runs the command in the
        // calling process's current directory.
        Dir string

        // Stdin specifies the process's standard input.
        // If Stdin is nil, the process reads from the null device (os.DevNull).
        // If Stdin is an *os.File, the process's standard input is connected
        // directly to that file.
        // Otherwise, during the execution of the command a separate
        // goroutine reads from Stdin and delivers that data to the command
        // over a pipe. In this case, Wait does not complete until the goroutine
        // stops copying, either because it has reached the end of Stdin
        // (EOF or a read error) or because writing to the pipe returned an error.
        Stdin io.Reader

        // Stdout and Stderr specify the process's standard output and error.
        //
        // If either is nil, Run connects the corresponding file descriptor
        // to the null device (os.DevNull).
        //
        // If Stdout and Stderr are the same writer, at most one
        // goroutine at a time will call Write.
        Stdout io.Writer
        Stderr io.Writer

        // ExtraFiles specifies additional open files to be inherited by the
        // new process. It does not include standard input, standard output, or
        // standard error. If non-nil, entry i becomes file descriptor 3+i.
        //
        // BUG(rsc): On OS X 10.6, child processes may sometimes inherit unwanted fds.
        // https://golang.org/issue/2603
        ExtraFiles []*os.File

        // SysProcAttr holds optional, operating system-specific attributes.
        // Run passes it to os.StartProcess as the os.ProcAttr's Sys field.
        SysProcAttr *syscall.SysProcAttr

        // Process is the underlying process, once started.
        Process *os.Process

        // ProcessState contains information about an exited process,
        // available after a call to Wait or Run.
        ProcessState *os.ProcessState
        // contains filtered or unexported fields
}

介绍如下：

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Cmd represents an external command being prepared or run.

A Cmd cannot be reused after calling its Run, Output or CombinedOutput methods.

可以看到局限性在于只能run一次。不过没关系，对于大部分情况是够用了的。

那么我们应该怎么去用这个东西呢？

go 标准库提供了这么一个函数用来创建cmd:

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func Command(name string, arg ...string) *Cmd

这个函数返回了一个填充了Path和Args的Cmd对象

如果说在name中有路径分隔符(path separator)，那么Command会自动在系统设定的path中寻找这个命令，如果没找到的话就直接把输入的name当作path。

我们只要用

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cmd := exec.Command("ls", "-a", "-l", "-h")  //实际可以直接写成-alh
b, err := cmd.CombinedOutput()

这样就可以获得到cmd执行后的结果。

在Cmd上有好几个函数可以做到获得输出，比较常用的是

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func (c *Cmd) CombinedOutput() ([]byte, error)

这个函数会先运行(run)这个cmd，然后再把stdout和stderr的输出放在一起返回。

除此之外，还有比如：

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func (c *Cmd) Output() ([]byte, error)

func (c *Cmd) Run() error

func (c *Cmd) Start() error

func (c *Cmd) StderrPipe() (io.ReadCloser, error)

func (c *Cmd) StdinPipe() (io.WriteCloser, error)

func (c *Cmd) StdoutPipe() (io.ReadCloser, error)

func (c *Cmd) Wait() error

等函数可以使用，具体可以查询标准库

除此之外，还有比如StartProcess之类的函数可以使用，大家可以自行尝试一下。