mjhjmtu

I got a task to do.

I have to search whether, are there running services on below ports.

ports 53 & 55

If not I have to send alerts.

Please correct my logic and syntax in below code for one port

ntstat=`netstat -tulpn | grep :53 | grep LISTEN | awk 'print $4'`
port="*:53"

#Just to echo for testing
echo $ntstat 
echo $port

if [[ "$ntstat" == "$port" ]];
then
 echo " X Service at port number $port"
else 
 echo " Port is not listing "
fi

Output :

127.0.1.1:53
*:53
Port is not listing 

I am struggling to match strings (127.0.1.1:53 to *:53)

You can also do a text-processing to your current output to match the port. Just add sed -e 's/.*:/:/g'

#!/bin/bash
ntstat=`netstat -tulpn | grep ":53 " | grep LISTEN | awk 'print $4' | sed -e 's/.*:/:/g'`
port=":53 "

#Just to echo for testing
echo $ntstat 
echo $port

if [[ "$ntstat" == "$port" ]]
then
 echo " X Service at port number $port"
else 
 echo " Port is not listing "
fi 

Please note that I added a space right after the port number in order to avoid other ports containing 53

Since this are bash operators, you must want to put the shebang #!/bin/bash at the very top of your script so when you execute your script as ./portlisten.sh, it will take the interpreter as /bin/bash, would be the same if you execute your script as $ bash portlisten.sh

To check if there are running services on ports 53(or 55) I would suggest the following optimized solution:

port=":53"
if netstat -tulpn | grep --line-buffered -q "$port .*LISTEN"; then
 echo " X Service at port number $port"
else 
 echo " Port is not listing "
fi

Don't use netstat since this is a deprecated command, use ss instead.

In your case you could use something like:

ss -H -o state listening '( sport = :53 or sport = :55 )'