in reply to references to subroutines

You want a dispatch table. 
my %dispatch = (
    add => \&add,
    multiple => \&multiply,
);

my ($action, @args) = @ARGV;

if ( exists $dispatch{ $action } ) {
    my $rv = $dispatch{ $action }->( @args );
    print "Result of '$action' is '$rv'\n";
}
else {
    warn "Invalid action '$action'\n";
}

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Also, look in List::Util for better versions of your add and multiply routines.

My criteria for good software:
  1. Does it work?
  2. Can someone else come in, make a change, and be reasonably certain no bugs were introduced?

In Section Seekers of Perl Wisdom