How to check whether a particular port is open on a machine from a shell script and perform action based on that?

The program lsof allows you to check which processes are using which ressources, like files or ports.

To show which processes are listening on port 8080:

lsof -Pi :8080 -sTCP:LISTEN

In your case, you want to test whether a process is listening on 8080 - the return value of this command tells you just that. It also prints the pid of the process.

lsof -Pi :8080 -sTCP:LISTEN -t

If you need just the test, with no output, redirect it to /dev/null:

if lsof -Pi :8080 -sTCP:LISTEN -t >/dev/null ; then
    echo "running"
else
    echo "not running"
fi

If you use multiple host names with multiple IP addresses locally, specify the hostname too like
lsof -Pi @someLocalName:8080 -sTCP:LISTEN

Simplest way in bash. Test if your port is open.

(echo >/dev/tcp/localhost/8080) &>/dev/null && echo "TCP port 8080 open" || echo "TCP port 8080 not open"

Replace the port with what you are testing.

Or you can use nc.

nc -vz 127.0.0.1 8080

Returns:

Connection to 127.0.0.1 8080 port [tcp/*] succeeded

Elaborating on RJ's answer which notes nc is also useful... Not only is nc useful for quick command-line query

❯ nc -z -v -w5 127.0.0.1 8080
localhost [127.0.0.1] 8080 (http-alt) : Connection refused

but it can be used without -v if the human-readability thing isn't what you're after -- e.g., for use in a script (the exit code will indicate whether the port is open or closed).

❯ nc -z 127.0.0.1 8080

❯ echo $?             
1