Do you mean that you want the program to use some sensible defaults if -p and -u are not given on the command-line? If that's the case, then the following snippet should help you on your way:

Getopt::Long::GetOptions(
   'u=s' => \$user,
   'p=s' => \$passwd,
);
$user   = 'me' unless defined $user;
$passwd = 'sekret' unless defined $passwd;
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If you can guarantee that neither $user nor $passwd can ever take the value 0, you can use the more compact expression:

$user   ||= 'me';
$passwd ||= 'sekret';
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... and when perl 5.10 is released (and we're in code freeze right now) the following will work, regardless of whether the value is 0 or not.

$user   //= 'me';
$passwd //= 'sekret';
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