If I understand correctly, you want to pass $r[0] back from sub interface_control to its caller? One way is to pass in a variable reference:

my $r;
my $s = ...;

interface_control($s, \$r);

# use $r here
...

sub interface_control
{
    my ($s, $r_ref) = @_;
    my (@r, $v, @h);
    $s->get_handles(rtrs=>\@r, vars=>\$v, hosts=>\@h);
    $$r_ref = $r[0];    # dereference $r_ref and write to its referent
    ...
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See perlreftut. (Or, of course, you could just return $r[0] at the end of the subroutine.)

Hope that helps,

The problem here is i can't modify interface_control. It is a global sub which is accessed by many users

@r, has list of routers r[0]....rn, . I want to display output only for r[0] and not for other router

If u see the below code ( under sub interface_control), i want to print blah only for r[0]. If i call interface_control($s), it may end up printing for all routers

  foreach my $rh (@r) {
  print ("blah blah");
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Here is one (inelegant) approach which might work for you:

#! perl
use strict;
use warnings;
use Capture::Tiny ':all';

my ($stdout, $stderr, @result) = capture
{
    interface_control();
};

my    @lines = split "\n", $stdout;
print $lines[0], "\n";

sub interface_control
{
    my @r;
    get_handles(\@r);
    print "blah blah for $_\n" for @r;
}

sub get_handles
{
    @{ $_[0] } = 11 .. 13;
}
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Output:

14:00 >perl 1204_SoPW.pl
blah blah for 11

14:00 >
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Update: Removed unnecessary parentheses from print statement, plus a blank line.

Hope that helps,

Athanasius <°(((>< contra mundum

Iustus alius egestas vitae, eros Piratica,

Well, then there is nothing you can do, short of doing something foolish like using PadWalker