#!/usr/bin/perl 
use strict;                     # Great start!

my @sample=qw(a,b,c);           # Declare array variable
&trial(\@sample);               # Pass array as a reference to sub
sub trial
{
   @sample=@_;                  # Clobber the contents of your original array
                                # setting the original array to the contents
                                # of the special array (@_), which just has
                                # a reference
   print join("\t",@$sample);   # Try to dereference a scalar variable named
                                # 'sample', which you never declared.
}

##</code><code>##

#!/usr/bin/perl 
use strict;
use warnings;

my @sample = qw(a b c);
trial(\@sample);
sub trial {
   my ($aref) = @_;
   print join "\t", @{ $aref };
}