使用netcat，你可以像这样检查端口是否打开:

nc my.example.com 80 < /dev/null

如果TCP端口被打开，nc的返回值为success，如果不能建立TCP连接，则返回值为failure(通常为返回码1)。

当你尝试这样做时，某些版本的nc会挂起，因为它们即使在从/dev/null.接收到文件结束后也不会关闭它们的套接字的发送部分在我自己的Ubuntu笔记本电脑(18.04)上，我安装的netcat-openbsd版本的netcat提供了一个变通方案:必须使用-N选项才能立即得到结果:

nc -N my.example.com 80 < /dev/null

在投票最多的答案的基础上，这里有一个等待两个端口打开的函数，还有一个超时。请注意必须打开的两个端口，8890和1111，以及max_attempts(每秒1次)。

function wait_for_server_to_boot()
{
    echo "Waiting for server to boot up..."
    attempts=0
    max_attempts=30
    while ( nc 127.0.0.1 8890 < /dev/null || nc 127.0.0.1 1111 < /dev/null )  && [[ $attempts < $max_attempts ]] ; do
        attempts=$((attempts+1))
        sleep 1;
        echo "waiting... (${attempts}/${max_attempts})"
    done
}

对nc使用-z和-w TIMEOUT选项很容易，但并不是所有的系统都安装了nc。如果你有一个最新版本的bash，这将工作:

# Connection successful:
$ timeout 1 bash -c 'cat < /dev/null > /dev/tcp/google.com/80'
$ echo $?
0

# Connection failure prior to the timeout
$ timeout 1 bash -c 'cat < /dev/null > /dev/tcp/sfsfdfdff.com/80'
bash: sfsfdfdff.com: Name or service not known
bash: /dev/tcp/sfsfdfdff.com/80: Invalid argument
$ echo $?
1

# Connection not established by the timeout
$ timeout 1 bash -c 'cat < /dev/null > /dev/tcp/google.com/81'
$ echo $?
124

What's happening here is that timeout will run the subcommand and kill it if it doesn't exit within the specified timeout (1 second in the above example). In this case bash is the subcommand and uses its special /dev/tcp handling to try and open a connection to the server and port specified. If bash can open the connection within the timeout, cat will just close it immediately (since it's reading from /dev/null) and exit with a status code of 0 which will propagate through bash and then timeout. If bash gets a connection failure prior to the specified timeout, then bash will exit with an exit code of 1 which timeout will also return. And if bash isn't able to establish a connection and the specified timeout expires, then timeout will kill bash and exit with a status of 124.

TOC:

使用bash和timeout 命令 例子 使用数控 命令 RHEL 6 (nc-1.84) 安装 例子 RHEL 7 (nmap-ncat-6.40) 安装 例子 讲话

使用bash和timeout:

请注意，超时应该在RHEL 6+中出现，或者在GNU coreutils 8.22中也可以找到。在MacOS上，使用brew install coreutils安装它，并将其用作gtimeout。

命令:

$ timeout $TIMEOUT_SECONDS bash -c "</dev/tcp/${HOST}/${PORT}"; echo $?

如果参数化主机和端口，请确保像上面那样将它们指定为${host}和${port}。不要仅仅将它们指定为$HOST和$PORT，即不带大括号;在这种情况下行不通。

例子:

成功:

$ timeout 2 bash -c "</dev/tcp/canyouseeme.org/80"; echo $?
0

失败:

$ timeout 2 bash -c "</dev/tcp/canyouseeme.org/81"; echo $?
124

如果必须保留bash的退出状态，

$ timeout --preserve-status 2 bash -c "</dev/tcp/canyouseeme.org/81"; echo $?
143

使用数控:

注意，在RHEL 7上安装了向后不兼容的nc版本。

命令:

注意，下面的命令是唯一的，因为它对于RHEL 6和7都是相同的。只是安装和输出不同而已。

$ nc -w $TIMEOUT_SECONDS -v $HOST $PORT </dev/null; echo $?

RHEL 6 （nc-1.84）：

安装:

$ sudo yum install nc

例子:

Success:

$ nc -w 2 -v canyouseeme.org 80 </dev/null; echo $?
Connection to canyouseeme.org 80 port [tcp/http] succeeded!
0

Failure:

$ nc -w 2 -v canyouseeme.org 81 </dev/null; echo $?
nc: connect to canyouseeme.org port 81 (tcp) timed out: Operation now in progress
1

如果主机名映射到多个ip，上述失败的命令将循环遍历多个或所有ip。例如:

$ nc -w 2 -v microsoft.com 81 </dev/null; echo $?
nc: connect to microsoft.com port 81 (tcp) timed out: Operation now in progress
nc: connect to microsoft.com port 81 (tcp) timed out: Operation now in progress
nc: connect to microsoft.com port 81 (tcp) timed out: Operation now in progress
nc: connect to microsoft.com port 81 (tcp) timed out: Operation now in progress
nc: connect to microsoft.com port 81 (tcp) timed out: Operation now in progress
1

RHEL 7 (nmap-ncat-6.40):

安装:

$ sudo yum install nmap-ncat

例子:

Success:

$ nc -w 2 -v canyouseeme.org 80 </dev/null; echo $?
Ncat: Version 6.40 ( http://nmap.org/ncat )
Ncat: Connected to 52.202.215.126:80.
Ncat: 0 bytes sent, 0 bytes received in 0.22 seconds.
0

Failure:

$ nc -w 2 -v canyouseeme.org 81 </dev/null; echo $?
Ncat: Version 6.40 ( http://nmap.org/ncat )
Ncat: Connection timed out.
1

如果主机名映射到多个ip，上述失败的命令将循环遍历多个或所有ip。例如:

$ nc -w 2 -v microsoft.com 81 </dev/null; echo $?
Ncat: Version 6.40 ( http://nmap.org/ncat )
Ncat: Connection to 104.43.195.251 failed: Connection timed out.
Ncat: Trying next address...
Ncat: Connection to 23.100.122.175 failed: Connection timed out.
Ncat: Trying next address...
Ncat: Connection to 23.96.52.53 failed: Connection timed out.
Ncat: Trying next address...
Ncat: Connection to 191.239.213.197 failed: Connection timed out.
Ncat: Trying next address...
Ncat: Connection timed out.
1

备注:

-v(——verbose)参数和回显$?命令当然只是为了说明。

正如B. Rhodes所指出的，nc (netcat)将完成这项工作。更紧凑的使用方法:

nc -z <host> <port>

这样，nc将只检查端口是否打开，成功时退出0，失败时退出1。

快速交互式检查(5秒超时):

nc -z -v -w5 <host> <port>

我猜现在给答案已经太迟了，而且这个答案可能不太好，但是你可以……

把它放在一个while循环中，并在上面加一个计时器。我更喜欢Perl而不是Solaris，但是根据你所使用的shell，你应该能够做一些像这样的事情:

TIME = 'date +%s' + 15
while TIME != `date +%s'
do whatever

然后在while循环中添加一个标志，这样如果它在完成之前超时，你可以引用超时作为失败的原因。

我怀疑telnet也有一个超时开关，但就我所知，我认为上面的方法是可行的。