ep_svr_<any number/s>_<3 letters>_<3 letters>_<any characters> 

#!/usr/bin/perl
if ($ARGV[0] =~ m/^ep_svr_\d+_[A-Za-z]{3}_[A-Za-z]{3}_\.+\z/x) {
	print "valid label: $ARGV[0]\n";
	}
else {
	print "invalid label: $ARGV[0]\n";
	};