perl function getservbyport

The getservbyport function is a built-in Perl function that is used to retrieve information about a specific network service from the system's service file. It takes the port number of the service as its argument and returns an array containing information about the service, such as the service's name and protocol.

Here's an example that demonstrates how to use getservbyport:

#!/usr/bin/perl

# Get information about the service running on port 80
$http_info = getservbyport(80, "tcp");

# Print the service's name
print "Service Name: $http_info->[0]\n";

In this example, we call getservbyport with the port number 80 and protocol "tcp" to retrieve information about the service running on that port. The information is returned as an array, which we assign to the variable $http_info. We then print the service's name using the array element at index 0.

Note that getservbyport will return undef if it is unable to find information about the specified service. Therefore, it's a good practice to check the return value of getservbyport before using the returned array.

#!/usr/bin/perl

# Get information about the service running on port 80
$http_info = getservbyport(80, "tcp");

# Check if service exists
if ($http_info) {
  # Print the service's name
  print "Service Name: $http_info->[0]\n";
} else {
  print "Service not found.\n";
}

In this updated example, we first check if the return value of getservbyport is defined using an if statement. If it is defined, we print the service's name as before. Otherwise, we print a message indicating that the service was not found.