怎么样通过linux shell脚本实现tcpupd协议通讯？

[chengmo@centos5 shell]$ cat</dev/tcp/127.0.0.1/22
SSH-2.0-OpenSSH_5.1
#我的机器shell端口是：22
#实际:/dev/tcp根本没有这个目录，这是属于特殊设备
[chengmo@centos5 shell]$ cat</dev/tcp/127.0.0.1/223
-bash: connect: 拒绝连接
-bash: /dev/tcp/127.0.0.1/223: 拒绝连接
#223接口不存在,打开失败

[chengmo@centos5 shell]$ exec 8<>/dev/tcp/127.0.0.1/22
[chengmo@centos5 shell]$ ls -l /proc/self/fd/
总计 0
lrwx------ 1 chengmo chengmo 64 10-21 23:05 0 -> /dev/pts/0
lrwx------ 1 chengmo chengmo 64 10-21 23:05 1 -> /dev/pts/0
lrwx------ 1 chengmo chengmo 64 10-21 23:05 2 -> /dev/pts/0
lr-x------ 1 chengmo chengmo 64 10-21 23:05 3 -> /proc/22185/fd
lrwx------ 1 chengmo chengmo 64 10-21 23:05 8 -> socket:[15067661]

#文件描述符8，已经打开一个socket通讯通道，这个是一个可以读写socket通道,因为用："<>"打开
[chengmo@centos5 shell]$ exec 8>&-
#关闭通道
[chengmo@centos5 shell]$ ls -l /proc/self/fd/
总计 0
lrwx------ 1 chengmo chengmo 64 10-21 23:08 0 -> /dev/pts/0
lrwx------ 1 chengmo chengmo 64 10-21 23:08 1 -> /dev/pts/0
lrwx------ 1 chengmo chengmo 64 10-21 23:08 2 -> /dev/pts/0
lr-x------ 1 chengmo chengmo 64 10-21 23:08 3 -> /proc/22234/fd

#!/bin/sh 
#testhttphead.sh
#实现通过主机名，端口读取web 服务器header信息
#copyright chengmo,qq:8292669

if(($#<2));then
echo "usage:$0 host port";
exit 1;
fi
#如果参数缺失，退出程序，返回状态1

exec 6<>/dev/tcp/$1/$2 2>/dev/null;
#打开host的port 可读写的socket连接，与文件描述符6连接

if(($?!=0));then
echo "open $1 $2 error!";
exit 1;
fi
#如果打开失败，$?返回不为0，终止程序

echo -e "HEAD / HTTP/1.1\n\n\n\n\n">&6; 
#将HEAD 信息，发送给socket连接

cat<&6; 
#从socket读取返回信息，显示为标准输出

exec 6<&-;
exec 6>&-; 
#关闭socket的输入，输出

exit 0;

[chengmo@centos5 ~/shell]$ sh testhttphead.sh www.baidu.com 80
HTTP/1.1 200 OK
Date: Thu, 21 Oct 2010 15:17:23 GMT
Server: BWS/1.0
Content-Length: 6218
Content-Type: text/html;charset=gb2312
Cache-Control: private
Expires: Thu, 21 Oct 2010 15:17:23 GMT
Set-Cookie: BAIDUID=1C40B2F8C676180FD887379A6E286DC1:FG=1; expires=Thu, 21-Oct-40 15:17:23 GMT; path=/; domain=.baidu.com
P3P: CP=" OTI DSP COR IVA OUR IND COM "
Connection: Keep-Alive

[chengmo@centos5 ~/shell]$ sh testhttphead.sh 127.0.0.1 8080
open 127.0.0.1 8080 error!

[chengmo@centos5 ~/shell]$ echo -e "HEAD / HTTP/1.1\n\n\n\n\n"|telnet www.baidu.com 80 
Trying 220.181.6.175...
Connected to www.baidu.com.
Escape character is '^]'.
Connection closed by foreign host.

#直接给发送，失败
[chengmo@centos5 ~/shell]$ (telnet www.baidu.com 80)<<EOF
HEAD / HTTP/1.1


EOF
Trying 220.181.6.175...
Connected to www.baidu.com.
Escape character is '^]'.
Connection closed by foreign host.
#重定向输入，还是失败？

[chengmo@centos5 shell]$ (echo -e "HEAD / HTTP/1.1\n\n\n\n\n";sleep 2)|telnet www.baidu.com 80 
Trying 220.181.6.175...
Connected to www.baidu.com.
Escape character is '^]'.
HTTP/1.1 200 OK
Date: Thu, 21 Oct 2010 15:51:58 GMT
Server: BWS/1.0
Content-Length: 6218
Content-Type: text/html;charset=gb2312
Cache-Control: private
Expires: Thu, 21 Oct 2010 15:51:58 GMT
Set-Cookie: BAIDUID=0B6A01ACECD5353E4247E088A8CB345A:FG=1; expires=Thu, 21-Oct-40 15:51:58 GMT; path=/; domain=.baidu.com
P3P: CP=" OTI DSP COR IVA OUR IND COM "
Connection: Keep-Alive
#成功了！加入sleep 居然可以了，sleep 改成1秒也可以

#!/bin/sh

#通过传入ip 以及端口，发送指令获得返回数据
#copyright chengmo qq:8292669

#函数往往放到最上面
function sendmsg()
{
msg=$1;
echo "$1">&8;
getout;
}
#向socket通道发送指令，并且调用获得返回参数

function getout()
{ 
#read 命令 -u 从打开文件描述符 8 读取数据，-d读取数据忽略掉:\r换行符 
while read -u 8 -d $'\r' name; 
do
if [ "${name}" == "END" -o "${name}" == "ERROR" ];then
break;
fi;
echo $name;
done
}
#由于：memcached每次通讯完毕，会返回：END或者ERROR(出错），通过判断是否是"END"觉得读取是不是结束，否则循环不会停止

if [ $# -lt 2 ];then
echo "usage:$0 host port [command]";
exit 1;
fi;

[[ $# -gt 2 ]]&&command=$3;

#设置默认值 如果command为定义则为：stats
command="${command=stats}";
host="$1";
port="$2";



exec 8<>/dev/tcp/${host}/${port};
#打开通向通道是8

if [ "$?" != "0" ];then
echo "open $host $port fail!";
exit 1;
fi

sendmsg "$command";
#发送指定命令


sendmsg "quit";
#发送退出通向命令


exec 8<&-;
exec 8>&-;
#关闭socket通道

exit 0;