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This command telnet and and looks for a line starting with "SSH" - works for OpenSSH since the SSH banner is something like "SSH-2.0-OpenSSH_6.0p1 Debian-4+deb7u3". Then it triggers an action accordingly.
It can be packed as a script file to echo 0/1 indicating the SSH service availability:
if [[ "$(sleep 1 | telnet -c <host> <port> 2>&1 | grep '^SSH')" == SSH* ]]; then echo 1; else echo 0; fi;
Trigger an action when server is UP (using &&):
[[ "$(sleep 1 | telnet -c <host> <port> 2>&1 | grep '^SSH')" == SSH* ]] && <command when up>
Trigger an action when server is DOWN (using ||):
[[ "$(sleep 1 | telnet -c <host> <port> 2>&1 | grep '^SSH')" == SSH* ]] || <command when down>
Almost same output with fewer typing... OP had a great idea : BOFH !!!
Super fast way to ftp/telnet/netcat/ssh/ping your loopback address for testing. The default route 0.0.0.0 is simply reduced to 0.
I'm flat-out surprised that minecraft directory services require servers install multiple modifications to their server code, when the directories could fetch this information on their own.
-z: Specifies that nc should just scan for listening daemons, without sending any data to them
-u: Use UDP instead of the default option of TCP.
Gets a BOFH excuse from the BOFH excuse server (towel.blinkenlights.nl port 666), and passes it through sed and tr to get rid of telnet connection stuff.
You are stuck with testing a tcp port using telnet, and must kill the telnet session from another terminal... Or, press ctrl+5 and write close/quit to force the current connection to close..
sends commands specified in $commandfile to the telnet-server specified by $telnetserver.
to have newlines in $commandfile interpreted as ENTER, save the file in CR+LF (aka "Windows-Textfile") format.
if you want to save the output in a separate file, use:
nc $telnetserver 23 < $commandfile > $resultfile
Use Ctrl-] to stop it.