Your code has many issues and I don't think the output corresponds to the code shown.

Most importantly don't use empty prototypes () and use warnings

Anyway this works for me and avoids printing undefined values. 

use strict;
use warnings;
use Getopt::Long;


GetOptions(
           'demo' => \&demo,
           'test' => \&test
          )
  or die("Error in command line arguments\n");


sub demo {
    my ( $arg0, $arg1, $arg2, $arg3, $arg4, $arg5 ) = @_ ;
    warn "Number of args: ", scalar @_;
    die "expected 2 args" if @_ != 2;
    warn join ",",@_;
}

sub test {
    die "expected 2 args" if @_ != 2;
    warn join ",",@_;
    demo("hello", "world");
}

[download]
OUTPUT: 
test,1 at d:/tmp/pm/getopt_long.pl line 23, <DATA> line 26.
Number of args: 2 at d:/tmp/pm/getopt_long.pl line 16, <DATA> line 26.
hello,world at d:/tmp/pm/getopt_long.pl line 18, <DATA> line 26.

[download]

Cheers Rolf
(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery

In reply to Re: Passing Parameters to subroutine by LanX
in thread Passing Parameters to subroutine by g_speran

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.