perl function getservbyname

The getservbyname 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 name of the service as its argument and returns an array containing information about the service, such as the service's port number and protocol.

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

#!/usr/bin/perl

# Get information about the "http" service
$http_info = getservbyname("http", "tcp");

# Print the service's port number
print "Port Number: $http_info->[2]\n";

In this example, we call getservbyname with the name "http" and protocol "tcp" to retrieve information about the HTTP service. The information is returned as an array, which we assign to the variable $http_info. We then print the service's port number using the array element at index 2.

Note that getservbyname 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 getservbyname before using the returned array.

#!/usr/bin/perl

# Get information about the "http" service
$http_info = getservbyname("http", "tcp");

# Check if service exists
if ($http_info) {
  # Print the service's port number
  print "Port Number: $http_info->[2]\n";
} else {
  print "Service not found.\n";
}

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