Here is an annotated version of your code to try and demonstrate the issue:

#!/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 origina
+l array
                                # setting the original array to the co
+ntents
                                # of the special array (@_), which jus
+t has
                                # a reference
   print join("\t",@$sample);   # Try to dereference a scalar variable
+ named
                                # 'sample', which you never declared.
}
[download]

use strict and warnings... warnings would also show another issue with your use of qw. Here is an improved version:

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

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

See also References quick reference

---

---

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! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

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:
	&		&
	<		&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.