kml.pl: Stub remove, set and usage modes

kml.pl

@@ -7,17 +7,42 @@ use warnings;
 use XML::LibXML;
 use URI::Escape;
 
-my ($name, $coordinates) = @ARGV;
-
 my $filename = 'ours.kml';
 my $dom = XML::LibXML->load_xml(location => $filename, no_blanks => 1);
 my $xpc = XML::LibXML::XPathContext->new($dom);
 $xpc->registerNs('k', "http://earth.google.com/kml/2.2");
 
+my $mode = shift;
+if ($mode eq 'add')
+{
+    my ($name, $coordinates) = @ARGV;
+    unless (defined($name) && defined($coordinates))
+    {
+        say "Not enough args for add operation";
+        USAGE(1);
+    }
     append_placemark($name, $coordinates, uri_escape($name));
-
     print $dom->toString(1);
+}
+elsif ($mode eq 'remove')
+{
+    say "Remove mode";
+}
+elsif ($mode eq 'set')
+{
+    say "Set mode";
+}
+else
+{
+    USAGE(1);
+}
 
+sub USAGE
+{
+    my $code = shift;
+    say "USAGE: ";
+    exit($code);
+}
 sub add_empty_child
 {
     my $node = shift;