# Figure out what actions the user wants to monitor.
my $monitored_actions = join "|", @ARGV;

# Create a monitoring RE that can be used again and again
# without re-compiling it.
my $monitor = qr/$monitored_actions/;

{
    # Decide what action to take.
    my $action = ('ADD', 'REMOVE', 'DELETE', 'QUIT')[rand(3)];

    # And here we monitor it.
    $action =~ /$monitor/ && do { print $action, "\n"; };

    redo unless $action eq 'QUIT';
}

##</code><code>##

./mytest ADD REMOVE