BTW, my test was to change the string used in the match and then see if $1 also changed. That isn't a perfect test because it might be that the string is copied but $1 doesn't correctly use the copy made, for example. Here is a more polished version and two sets of results:

#!/usr/bin/perl -w
use strict;

print "$] $^O\n";
for(  qw( s l sg lg )  ) {
    my $x= "-y1-y2-";
    my @y;
    $y[0]= $x =~ /(.\d)/
        if  's' eq $_;
    @y= $x =~ /(.\d)/
        if  'l' eq $_;
    $y[0]= $x =~ /(.\d)/g
        if  'sg' eq $_;
    @y= $x =~ /(.\d)/g
        if  'lg' eq $_;
    $x= ":1n:2n:";
    print "$_ ($1)\n";
}
__END__

5.006 MSWin32
s (y1)
l (1n)
sg (1n)
lg (2n)

5.008008 MSWin32
s (y1)
l (y1)
sg (1n)
lg (2n)
[download]

Which shows I'd missed the only "will copy" case in 5.6.