@s = ("foo bar baz") x 4;
$bar = "rab";
%bar = (1 => "eek");
@bar = (undef, 'oof');

$s[0] =~ s{(bar)} {$bar\{1\}};
$s[1] =~ s{(bar)} [$bar\{1\}];

$s[2] =~ s{(bar)} {$bar\[1\]};
$s[3] =~ s{(bar)} [$bar\[1\]];

for $i (0..3)
{ print "$i -> '$s[$i]'\n"; }