詳解golang執行Linux shell命令完整場景下的使用方法

2022-06-30 14:02:26

1. 執行命令並獲得輸出結果

CombinedOutput()

執行程式返回 standard output and standard error

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

Output()

執行程式返回standard output

func main() {
    out, err := exec.Command("date").Output()
    if err != nil {
        log.Fatal(err)
    }
    fmt.Printf("The date is %sn", out)
}

2. 將stdout和stderr分別處理

用buffer接受輸出

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

直接列印到螢幕

func main() {
    cmd := exec.Command("ls", "-lah")
    cmd.Stdout = os.Stdout
    cmd.Stderr = os.Stdout
    err := cmd.Run()
    if err != nil {
        log.Fatalf("cmd.Run() failed with %sn", err)
    }
}

3. 非同步執行命令

cmd.Run() 阻塞等待命令執行結束
cmd.Start() 不會等待命令完成

package main

import (
    "bytes"
    "fmt"
    "io"
    "log"
    "os"
    "os/exec"
)

func main() {
    var stdoutBuf, stderrBuf bytes.Buffer
    cmd := exec.Command("bash", "-c", "for i in 1 2 3 4;do echo $i;sleep 2;done")
    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 %sn", err)
    }
    if errStdout != nil || errStderr != nil {
        log.Fatal("failed to capture stdout or stderrn")
    }
    outStr, errStr := string(stdoutBuf.Bytes()), string(stderrBuf.Bytes())
    fmt.Printf("nout:n%snerr:n%sn", outStr, errStr)
}

4. 執行時帶上環境變數

func main() {
    cmd := exec.Command("bash", "-c", "programToExecute")
    additionalEnv := "programToExecute=ls"
    newEnv := append(os.Environ(), additionalEnv)
    cmd.Env = newEnv
    out, err := cmd.CombinedOutput()
    if err != nil {
        log.Fatalf("cmd.Run() failed with %sn", err)
    }
    fmt.Printf("%s", out)
}

5. 預先檢查命令是否存在

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

6. 兩個命令依次執行，管道通訊

func main() {
    c1 := exec.Command("ls")
    c2 := exec.Command("wc", "-l")
    r, w := io.Pipe() 
    c1.Stdout = w
    c2.Stdin = r
    var b2 bytes.Buffer
    c2.Stdout = &b2
    c1.Start()
    c2.Start()
    c1.Wait()
    w.Close()
    c2.Wait()
    io.Copy(os.Stdout, &b2)
}

或者

func main() {
    c1 := exec.Command("ls")
    c2 := exec.Command("wc", "-l")
    c2.Stdin, _ = c1.StdoutPipe()
    c2.Stdout = os.Stdout
    _ = c2.Start()
    _ = c1.Run()
    _ = c2.Wait()
}

反正下面這樣是不行的

func main() {
    c := exec.Command("ls", "|", "wc", "-l")
    c.Stdout = os.Stdout
    _ = c.Run()
}

不嫌醜可以用bash -c

func main() {
    cmd := "cat /proc/cpuinfo | egrep '^model name' | uniq | awk '{print substr($0, index($0,$4))}'"
    out, err := exec.Command("bash", "-c", cmd).Output()
    if err != nil {
        fmt.Printf("Failed to execute command: %s", cmd)
    }
    fmt.Println(string(out))
}

7. 按行讀取輸出內容

func main() {
    cmd := exec.Command("ls", "-la")
    stdout, _ := cmd.StdoutPipe()
    cmd.Start()
    reader := bufio.NewReader(stdout)
    for {
        line, err := reader.ReadString('n')
        line = strings.TrimSpace(line)
        if err != nil || io.EOF == err {
            break
        }
        log.Println(line)
    }
    cmd.Wait()
}

8. 獲得exit code

func RunCommand(name string, args ...string) (stdout string, stderr string, exitCode int) {
    log.Println("run command:", name, args)
    var outbuf, errbuf bytes.Buffer
    cmd := exec.Command(name, args...)
    cmd.Stdout = &outbuf
    cmd.Stderr = &errbuf

    err := cmd.Run()
    stdout = outbuf.String()
    stderr = errbuf.String()

    if err != nil {
        // try to get the exit code
        if exitError, ok := err.(*exec.ExitError); ok {
            ws := exitError.Sys().(syscall.WaitStatus)
            exitCode = ws.ExitStatus()
        } else {
            // This will happen (in OSX) if `name` is not available in $PATH,
            // in this situation, exit code could not be get, and stderr will be
            // empty string very likely, so we use the default fail code, and format err
            // to string and set to stderr
            log.Printf("Could not get exit code for failed program: %v, %v", name, args)
            exitCode = defaultFailedCode
            if stderr == "" {
                stderr = err.Error()
            }
        }
    } else {
        // success, exitCode should be 0 if go is ok
        ws := cmd.ProcessState.Sys().(syscall.WaitStatus)
        exitCode = ws.ExitStatus()
    }
    log.Printf("command result, stdout: %v, stderr: %v, exitCode: %v", stdout, stderr, exitCode)
    return
}

參考連結：

https://saucer-man.com/backend_development/571.html

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