Köra script när ethernetnätverk aktiveras i OSX

#!/usr/bin/perl

# This little thingy poll a chosen network interface once every minute to decide if it's active
# and if it has a certain IP-adress. If both are true, a second script is executed. A script is
# also executed when the interface goes down again.

# Script config
$interface = 'en0';
$ip_pattern = '192\.168\.0\.\d+'; #Regular expressions FTW!
$script_up = '/Users/macke/backup.pl'; #Keep it empty to not run a script
$script_down = ''; #Like the one above

# Beginning of script
$up = 0; #This keeps track of the status of the interface, $script_up/down will only be executed on a change
$verbose = 1 if @ARGV[0] eq '-v'; #If -v is passed to the script some status messages will be printed to STDOUT

while(1)
{
	#Grabbing the status if the interface
	$ifconfig = `ifconfig $interface`;
	
	if($ifconfig =~ /status: active/ and not $up)
	{
		print "Interface is up\n" if $verbose;
		#Checking if it is the IP-adress we want
		if($ifconfig =~ /inet $ip_pattern/)
		{
			#Interface went up
	 		print "IP is matching\n" if $verbose;
	 		$up = 1;
	 		system($script_up) if $script_up ne '';
		}
	}
	elsif($ifconfig =~ /status: inactive/ and $up)
	{
		#Interface went down
		print "Interface is down\n" if $verbose;
		$up = 0;
		system($script_down) if $script_down ne '';
	}
	#Sleeping for 60 seconds
	sleep 60;
}