继续从 tcp 服务器读取，直到收到特定消息答案

【问题标题】：Keep reading from tcp server until a certain message is received继续从 tcp 服务器读取，直到收到特定消息
【发布时间】：2018-10-01 17:08:53
【问题描述】：

我有以下代码：

 echo "about to echo stuff 1";

 echo -e "foo\n" | nc localhost "${ql_server_port}" | while read response; do
         echo "response from server: $response";
         if [[ "$response" == "released" ]]; then
            echo "quicklock: Lock was released.";
            return 0;
         fi
   done;

 echo "about to echo stuff 2";

这是记录的内容：

about to echo stuff 1
response from server: received_data
about to echo stuff 2

我不明白为什么它不继续从 netcat 连接读取，似乎在收到第一条消息后停止读取。有人知道如何从连接中继续读取吗？

我的猜测是管道关闭是因为 echo 语句退出？如果是这样，如何保持打开状态？

【问题讨论】：

我问了这个问题 - github.com/nodejs/help/issues/1228

标签： bash shell tcp netcat

【解决方案1】：

文件描述符重定向到救援

# make a copy of stdout
exec  3<&1
echo "about to echo stuff 1";

# read from fd 3
{ nc localhost 1234 <3 | while read response; do
    echo "response from server: $response";
    if [[ "$response" == "released" ]]; then
        echo "quicklock: Lock was released."
        break
    fi
done } &

# echo to stdout but redirect to fd 3
echo -e "foo\n" >3
echo -e "bar\n" >3
# close descriptor when done
exec  3<&-
# wait for comm to finish
sleep 2
echo "about to echo stuff 2";

输出

about to echo stuff 1
response from server: bin
response from server: gar
response from server: released
quicklock: Lock was released.
about to echo stuff 2

【讨论】：

是的，我做了一些研究，您需要做的就是保持第一个进程打开。 echo 将在写入标准输出后消失。如果您创建一个在写入标准输出后仍保持活动状态的进程，那么这就是您所需要的。

【解决方案2】：

这可行，但如果可能的话，我正在寻找一种更简单的方法：

     local named_pipe="$HOME/.quicklock/named_pipes/$$";
     mkfifo ${named_pipe};

      tail -f ${named_pipe} | nc localhost "${ql_server_port}" | while read response; do
         echo "response from server: $response";
         if [[ "$response" == "released" ]]; then
            echo "quicklock: Lock was released.";
            return 0;
         fi
      done &
   fi


     echo -e "{\"quicklock\":true}\n" > ${named_pipe}
     wait;

有没有办法回显某些内容，但不关闭进程？

【讨论】：