Congratulations on use of warnings and strict. You'll save much heartache down the road that way.

my $op = shift @ARGV;
# first element of @ARGV now in $op and removed from @ARGV.

print add(@ARGV) . "\n"  if $op eq 'add';
print multiply(@ARGV) . "\n"  if $op eq 'multiply';
# subs as before
[download]

Or you can get fancy and have a hash table of functions:

my $op = shift @ARGV;
# first element of ARGV in $op and removed from @ARGV.

my %h = ( add => \&add, multiply => \&multiply);

print $h{$op}->(@ARGV) . "\n";

# subs as before
[download]

--Bob Niederman, http://bob-n.com