Check status of one port on remote host [closed]

You seem to be looking for a port scanner such as nmap or netcat, both of which are available for Windows, Linux, and Mac OS X.

For example, check for telnet on a known ip:

nmap -A 192.168.0.5/32 -p 23

For example, look for open ports from 20 to 30 on host.example.com:

nc -z host.example.com 20-30

In Command Prompt, you can use the command telnet.. For Example, to connect to IP 192.168.10.1 with port 80,

telnet 192.168.10.1 80

To enable telnet in Windows 7 and above click. From the linked article, enable telnet through control panel -> programs and features -> windows features -> telnet client, or just run this in an admin prompt:

dism /online /Enable-Feature /FeatureName:TelnetClient

For scripting purposes, I've found that curl command can do it, for example:

$ curl -s localhost:80 >/dev/null && echo Connected. || echo Fail.
Connected.
$ curl -s localhost:123 >/dev/null && echo Connected. || echo Fail.
Fail.

Possibly it may not won't work for all services, as curl can return different error codes in some cases (as per comment), so adding the following condition could work in reliable way:

[ "$(curl -sm5 localhost:8080 >/dev/null; echo $?)" != 7 ] && echo OK || echo FAIL

^{Note: Added -m5 to set maximum connect timeout of 5 seconds.}

If you would like to check also whether host is valid, you need to check for 6 exit code as well:

$ curl -m5 foo:123; [ $? != 6 -a $? != 7 ] && echo OK || echo FAIL
curl: (6) Could not resolve host: foo
FAIL

To troubleshoot the returned error code, simply run: curl host:port, e.g.:

$ curl localhost:80
curl: (7) Failed to connect to localhost port 80: Connection refused

See: man curl for full list of exit codes.