golang 使用os/exec执行命令

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go语言用来执行一切系统的命令相对python来说还是有点复杂的，执行命令是一个非常常见的需求，如调用一个系统命令，启一个exe等。

执行命令并获得输出结果

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func main() {
	cmd := exec.Command("ls", "-lah")
	out, err := cmd.CombinedOutput()
	if err != nil {
		log.Fatalf("cmd.Run() failed with %s\n", err)
	}
	fmt.Printf("combined out:\n%s\n", string(out))
}

将stdout和stderr分别处理

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func main() {
	cmd := exec.Command("ls", "-lah")
	var stdout, stderr bytes.Buffer
	cmd.Stdout = &stdout
	cmd.Stderr = &stderr
	err := cmd.Run()
	if err != nil {
		log.Fatalf("cmd.Run() failed with %s\n", err)
	}
	outStr, errStr := string(stdout.Bytes()), string(stderr.Bytes())
	fmt.Printf("out:\n%s\nerr:\n%s\n", outStr, errStr)
}
``` 

### 命令执行过程中获得输出
```go
func main() {
	var stdoutBuf, stderrBuf bytes.Buffer
	cmd := exec.Command("ls", "-lah")
	stdoutIn, _ := cmd.StdoutPipe()
	stderrIn, _ := cmd.StderrPipe()
	var errStdout, errStderr error
	stdout := io.MultiWriter(os.Stdout, &stdoutBuf)
	stderr := io.MultiWriter(os.Stderr, &stderrBuf)
	err := cmd.Start()
	if err != nil {
		log.Fatalf("cmd.Start() failed with '%s'\n", err)
	}
	go func() {
		_, errStdout = io.Copy(stdout, stdoutIn)
	}()
	go func() {
		_, errStderr = io.Copy(stderr, stderrIn)
	}()
	err = cmd.Wait()
	if err != nil {
		log.Fatalf("cmd.Run() failed with %s\n", err)
	}
	if errStdout != nil || errStderr != nil {
		log.Fatal("failed to capture stdout or stderr\n")
	}
	outStr, errStr := string(stdoutBuf.Bytes()), string(stderrBuf.Bytes())
	fmt.Printf("\nout:\n%s\nerr:\n%s\n", outStr, errStr)
}

改变执行程序的环境(environment)

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cmd := exec.Command("programToExecute")
additionalEnv := "FOO=bar"
newEnv := append(os.Environ(), additionalEnv))
cmd.Env = newEnv
out, err := cmd.CombinedOutput()
if err != nil {
	log.Fatalf("cmd.Run() failed with %s\n", err)
}
fmt.Printf("%s", out)

预先检查程序是否存在

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func checkLsExists() {
	path, err := exec.LookPath("ls")
	if err != nil {
		fmt.Printf("didn't find 'ls' executable\n")
	} else {
		fmt.Printf("'ls' executable is in '%s'\n", path)
	}
}