“exec.Command()”在运行“kcat”时没有输出

本篇文章主要是结合我之前面试的各种经历和实战开发中遇到的问题解决经验整理的，希望这篇《“exec.Command()”在运行“kcat”时没有输出》对你有很大帮助！欢迎收藏，分享给更多的需要的朋友学习~

我需要将 kcat 包装在 go 函数中来读取一系列主题消息，因此考虑使用 exec.command() ，如下所示：

package main

import (
    "fmt"
    "os/exec"
)

func main() {

    cmd := exec.command("kcat", "-b kafka.kafka.svc.cluster.local:9092", "-t messages", "-o 11000", "-c 11333")

    fmt.println("command string:", cmd.string())

    out, err := cmd.combinedoutput()

    if err != nil {
        fmt.println("error accessing kafka topic messages ", err.error(), string(out))
        return
    }

    fmt.println("result length:", len(out))

    fmt.println("result content:", string(out))

}

但是，这仅返回 kcat 输出的第一行：

/app/tools # ./five
command string: /usr/bin/kcat -b kafka.kafka.svc.cluster.local:9092 -t messages -o 11000 -c 11333
result length: 58

result content: % auto-selecting producer mode (use -p or -c to override)

（注意：我在 docker 容器中运行它，但我认为这没有什么区别）

但是，直接从 cli 运行时效果很好：

/app/tools # 
/app/tools # kcat -b kafka.kafka.svc.cluster.local:9092 -t messages -o 10 -c 15
% auto-selecting consumer mode (use -p or -c to override)
%4|1640957136.462|offset|rdkafka#consumer-1| [thrd:main]: messages [1]: offset reset (at offset 10) to end: fetch failed due to requested offset not available on the broker: broker: offset out of range
%4|1640957136.483|offset|rdkafka#consumer-1| [thrd:main]: messages [2]: offset reset (at offset 10) to end: fetch failed due to requested offset not available on the broker: broker: offset out of range
[{"name":"neworder", "id":"9266","time":"9266","data":"new order", "eventname":"neworder"}]

[{"name":"neworder", "id":"1547","time":"1547","data":"new order", "eventname":"neworder"}]

[{"name":"neworder", "id":"9179","time":"9179","data":"new order", "eventname":"neworder"}]

[{"name":"neworder", "id":"8740","time":"8740","data":"new order", "eventname":"neworder"}]

[{"name":"neworder", "id":"9318","time":"9318","data":"new order", "eventname":"neworder"}]

[{"name":"neworder", "id":"1743","time":"1743","data":"new order", "eventname":"neworder"}]

kcat 命令似乎有一些独特之处，它会破坏 go 中的 exec.command() 。

问题：

• 还有其他方法可以在 go 中实现相同的效果吗？
• 这可能是我使用 exec.command() 方式的问题

理想情况下，我可以在这种情况下使用 kcat 命令，因为我想避免在这种情况下使用segmentios kafka-go 库。

[编辑]

• 分隔参数（按照 @onecricketeer 的建议）：

cmd := exec.command("kcat", "-b", "kafka.kafka.svc.cluster.local:9092", "-t", "messages", "-o", "11000", "-c", "11333")

结果（相同的错误）：

/app/tools # ./code
command string: /usr/bin/kcat -b kafka.kafka.svc.cluster.local:9092 -t messages -o 11000 -c 11333
result length: 58
result content: % auto-selecting producer mode (use -p or -c to override)

• 使用 bash 作为 shell（maxm 建议）：

相同的结果，即仅报告 kcat 输出的第一行：

/app/tools # ./code
command string: /bin/bash -c kcat -b kafka.kafka.svc.cluster.local:9092 -t messages -o 11000 -c 11333
result length: 58
result content: % auto-selecting producer mode (use -p or -c to override)

[编辑]

注意：但是，当我使用python的shell执行机制时，它运行得很好，这让我怀疑gos的shell处理功能是否存在缺陷：

import subprocess

process = subprocess.popen(["kcat","-b","kafka.kafka.svc.cluster.local:9092","-t","messages","-o","1", "-c", "11"], 
                           stdout=subprocess.pipe,
                           universal_newlines=true)

while true:
    output = process.stdout.readline()
    print(output.strip())
    # do something else
    return_code = process.poll()
    if return_code is not none:
        print('return code', return_code)
        # process has finished, read rest of the output 
        for output in process.stdout.readlines():
            print(output.strip())
        break

结果：

/app/tools/python # python3 code.py 
% Auto-selecting Consumer mode (use -P or -C to override)
%4|1641004616.232|OFFSET|rdkafka#consumer-1| [thrd:main]: messages [2]: offset reset (at offset 1) to END: fetch failed due to requested offset not available on the broker: Broker: Offset out of range
%4|1641004616.236|OFFSET|rdkafka#consumer-1| [thrd:main]: messages [1]: offset reset (at offset 1) to END: fetch failed due to requested offset not available on the broker: Broker: Offset out of range
[{"Name":"newOrder", "ID":"4512","Time":"4512","Data":"new order", "Eventname":"newOrder"}]

RETURN CODE 0
[{"Name":"newOrder", "ID":"2388","Time":"2388","Data":"new order", "Eventname":"newOrder"}]

[{"Name":"newOrder", "ID":"8707","Time":"8707","Data":"new order", "Eventname":"newOrder"}]

[{"Name":"newOrder", "ID":"1643","Time":"1643","Data":"new order", "Eventname":"newOrder"}]

[{"Name":"newOrder", "ID":"2421","Time":"2421","Data":"new order", "Eventname":"newOrder"}]

[{"Name":"newOrder", "ID":"7520","Time":"7520","Data":"new order", "Eventname":"newOrder"}]

[{"Name":"newOrder", "ID":"1258","Time":"1258","Data":"new order", "Eventname":"newOrder"}]

[{"Name":"newOrder", "ID":"1457","Time":"1457","Data":"new order", "Eventname":"newOrder"}]

[{"Name":"newOrder", "ID":"2907","Time":"2907","Data":"new order", "Eventname":"newOrder"}]

[{"Name":"newOrder", "ID":"9266","Time":"9266","Data":"new order", "Eventname":"newOrder"}]

[{"Name":"newOrder", "ID":"1547","Time":"1547","Data":"new order", "Eventname":"newOrder"}]

正确答案

正如输出所示，正在自动选择生产者模式

尝试使用带有分隔参数的消费者模式

cmd := exec.command("kcat", "-c", "-b", "kafka.kafka.svc.cluster.local:9092", "-t", "messages", "-o", "11000", "-c", "11333")

go 命令：

cmd := exec.command("kcat", "-b kafka.kafka.svc.cluster.local:9092", "-t messages", "-o 11000", "-c 11333")

与shell命令相同：

kcat "-b kafka.kafka.svc.cluster.local:9092" "-t messages" "-o 11000" "-c 11333"

您需要分隔参数，就像 shell 默认在每个空格上为您所做的那样：

cmd := exec.Command("kcat", "-b", "kafka.kafka.svc.cluster.local:9092", "-t", "messages", "-o", "11000", "-c", "11333")

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