沉默/dev/tcp/host/port重定向错误 [英] Silence /dev/tcp/host/port redirection errors

问题描述

以下脚本将测试从8079到8081的tcp端口是打开还是关闭.

The following script will test if tcp port from 8079 to 8081 is open or closed.

for port in {8079..8081}; do
  echo >/dev/tcp/127.0.0.1/$port &&
    echo "port $port is open" ||
    echo "port $port is closed"
done

输出

user@linux:~$ ./script.sh 
./script.sh: connect: Connection refused
./script.sh: line 2: /dev/tcp/127.0.0.1/8079: Connection refused
port 8079 is closed
port 8080 is open
./script.sh: connect: Connection refused
./script.sh: line 2: /dev/tcp/127.0.0.1/8081: Connection refused
port 8081 is closed
user@linux:~$ 

如何删除以下几行?我曾尝试将stderr重定向到/dev/null ，例如 2>/dev/null ，但是没有用.

How do I remove the following lines? I've tried to redirect stderr to /dev/null like 2>/dev/null but didn't work.

./script.sh: connect: Connection refused
./script.sh: line 2: /dev/tcp/127.0.0.1/8079: Connection refused

所需的输出

user@linux:~$ ./script.sh 
port 8079 is closed
port 8080 is open
port 8081 is closed
user@linux:~$ 

推荐答案

我试图将stderr重定向到/dev/null，如2>/dev/null一样，但是没有用.

I've tried to redirect stderr to /dev/null like 2>/dev/null but didn't work.

实际上是可行的.只是您需要重定向整个循环的stderr ^* ，而不仅仅是重定向 echo 的stderr ^* .因为不是 echo 报告这些错误.例如:

Actually it works. It's just you need to redirect the whole loop's stderr^*, not just echo's; as it's not echo that reports those errors. E.g:

for port in {8079..8081}; do
  if echo >/dev/tcp/127.0.0.1/$port; then
    echo "port $port is open"
  else
    echo "port $port is closed"
  fi
done 2>/dev/null

^* 或if块，或 echo 范围之外的任何内容.无论是标准手册还是bash手册都没有明确说明其工作原理，我想这只是常识.

^* Or the if block, or whatever beyond the scope of echo. Neither the standard nor bash manual makes an explicit remark on why this works, I guess it's just common sense.

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