当发生客户端连接时，接受TCP连接的Bash脚本将一天中的时间作为对客户端的响应发送。

Question

我不想撒谎，这是一项家庭作业，但我一直在谷歌，试图了解如何处理这个特定的问题。

“创建一个名为lab6s6的脚本，该脚本接受TCP连接。当发生客户端连接时，发送一天中的时间作为对客户端的响应。您可以选择任何端口号作为侦听端口，并且不要忘记关闭连接。”

我正在我的virtualbox上运行最新的fedora操作系统

到目前为止，在做了一些研究之后，我遇到了一段特定的代码

$ exec {file-descriptor}<>/dev/{protocol}/{host}/{port}

我做了一些研究后想出来的是

exec 3<>/dev/TCP/127.0.0.1/8000

因此，根据我的一般理解，文件描述符总是被设置为3(这是因为stdin，stdout，stderr，这是为了什么目的？)还有表示读写的"<>“，目录是实际使用这些协议的一种方式。最后，对于我的ip，我读到的某个地方，我不应该使用这个环回，这是行不通的，但老实说，我在读这篇文章的时候有点不知所措，而对于端口，我从来没有真正理解这一点，是不是就像你的信号越多？

另外一个问题是，我是否需要安装任何其他类型的软件才能完成这样的任务？如果有人能澄清我是否基本上像我的电脑上的电话线一样开放，以便能够在我的局域网上与其他计算机通话，这可能吗？

我不是在要求直接的回答，但是如果有人能把我推向正确的方向，我会非常感激的！

再次感谢！

Answer 1

我已经为您准备了两个脚本:客户机和服务器，在授予它们执行权限之后: chmod u+x script_name，您可以按任何顺序运行它们(客户机、->服务器或服务器->客户机)。

bash_server.sh

#!/usr/bin/env bash

#define port on which the server will listen
#and the output file that will be used to store the client port to send an answer
readonly PORT_LISTEN=22222;
readonly SERVER_FILE=server_file_tmp.out;

echo "Removing the server temporary file: ${SERVER_FILE}";
rm -f "${SERVER_FILE}";
#will open/bind/listen on PORT_LISTEN and whenever some information is received 
#it will write it in the SERVER FILE
echo "Starting the server on port: ${PORT_LISTEN} with configuration file: ${SERVER_FILE}";
nc -k -l "${PORT_LISTEN}" | tee "${SERVER_FILE}" &

echo "Waiting for connection..."
#active listening to entry connection
while true; 
do
    #get always information about the external connection trying to connect to our open port
    tmpNetworkString=$(lsof -i:"${PORT_LISTEN}" | grep "localhost:${PORT_LISTEN} (ESTABLISHED)" | awk '{print $9}');
    echo -n "${tmpNetworkString}";
    if [ -s "${SERVER_FILE}" ] && [ ! -z "${tmpNetworkString}" ]; then
        answerPORT=$(cat "${SERVER_FILE}");
        echo "Connection received on port ${PORT_LISTEN}...";
        incomingIP=$(echo $tmpNetworkString | cut -d':' -f1);
        incomingPort=$(echo $tmpNetworkString | cut -d'-' -f1 | cut -d':' -f2);
        echo ">>Incoming traffic IP: ${incomingIP}";
        echo ">>Incoming traffic Port: ${incomingPort}";
        echo "Answering on IP: ${incomingIP}, port: ${answerPORT}...";
        #wait client port to be ready
        nc -z "${incomingIP}" "${answerPORT}";
        isOpen=$?;
        while [ ! "${isOpen}" -eq 0 ];
        do
            nc -z "${incomingIP}" "${answerPORT}";
            isOpen=$?;
        done
        echo $(date) | nc -q 2 "${incomingIP}" "${answerPORT}";
        echo "Closing the server, port: ${PORT_LISTEN}";
        fuser -k -n tcp "${PORT_LISTEN}";
        echo "Removing the server temporary file: ${SERVER_FILE}";
        rm -f "${SERVER_FILE}";
        exit 0;
    fi
done

bash_client.sh

#!/usr/bin/env bash

#define port on which the client will listen
#and the output file that will be used to store the answer from the server
readonly PORT_LISTEN=33333;
readonly CLIENT_FILE=client_file_tmp.out;
readonly SERVER_PORT=22222;
readonly SERVER_IP=localhost

echo "Removing the client temporary file: ${CLIENT_FILE}";
rm -f "${CLIENT_FILE}";
#will open/bind/listen on PORT_LISTEN and whenever some information is received 
#it will write it in the CLIENT FILE
echo "Starting the server on port: ${PORT_LISTEN} with configuration file: ${CLIENT_FILE}";
nc -k -l "${PORT_LISTEN}" > "${CLIENT_FILE}" &

echo "Connecting to the server: ${SERVER_IP}, on port: ${SERVER_PORT} and waiting for answer";
#sending port information for answer:

#wait client port to be ready
nc -z "${SERVER_IP}" "${SERVER_PORT}";
isOpen=$?;
while [ ! "${isOpen}" -eq 0 ];
do
    nc -z "${SERVER_IP}" "${SERVER_PORT}";
    isOpen=$?;
done
echo "${PORT_LISTEN}" | nc -q 2 "${SERVER_IP}" "${SERVER_PORT}";

while true; 
do
    if [ -s "${CLIENT_FILE}" ]; then
        echo "Answer received from server...";
        echo "##############################";
        echo "##############################";
        cat "${CLIENT_FILE}";
        echo "##############################";
        echo "##############################";
        #sleep 10;
        echo "Closing the open port of the client, port: ${PORT_LISTEN}";
        fuser -k -n tcp "${PORT_LISTEN}";
        echo "Removing the answer file: ${CLIENT_FILE}";
        rm -f "${CLIENT_FILE}";
        exit 0;
    fi
done