actually I am using forks module instead of the threads module

In that case, you can simply assign to $0, which has been working fine for ages (on Linux, and for processes) — i.e. you don't need 5.13:

#!/usr/bin/perl

use forks;

my @procs;

for my $procname (qw(foo bar baz)) {
    push @procs,
        threads->new(
            sub {
                $0 = $procname;
                sleep 1;
            }
        );
}

system "ps fT -o pid,cmd";

$_->join() for @procs;

__END__
$ ./837477.pl
  PID CMD
10408 bash -rcfile .bashrc
 5278  \_ /usr/bin/perl ./837477.pl
 5279      \_ /usr/bin/perl ./837477.pl
 5280      \_ foo
 5281      \_ bar
 5282      \_ baz
 5283      \_ ps fT -o pid,cmd
[download]

(the foo/bar/baz are your "forks-threads")

Thanks almut, what should i write in the place of following system command, if I write it in solaris platform system "ps fT -o pid,cmd"

Almut, I tried but unable to set/change the name in perl 5.8 running on Solaris Server 10

There's a reason I said Linux... :)

The problem is that setting $0 is not implemented for Solaris, at least not in a way that would work.  AFAIK, that's because (a) there is no system support for it (in the form of setproctitle(), etc.), so you'd have to resort to manipulating argv[] directly at the C level, and (b) the normal tools like ps (i.e. /usr/bin/ps) or ptree don't read the command+args from argv[] anyway, but rather from some other, harder to manipulate location, so you'd have to use /usr/ucb/ps (whose output can - to some degree - be influenced by a modified argv[]).

In case I have the time later, I'll see whether I can whip up a little XS routine which would allow to change the command name as it's shown by /usr/ucb/ps...