## perl 5.10.1
use strict;
use warnings;

my $oo;
my @ary = ( 0, 1, 2, 3);

grep $ary[$_ ], @ary;  # no warning

grep $ary[$oo], @ary;  # warns

##</code><code>##

## perl 5.10.1
use strict;
use warnings;

print $_;   # warns

my ( $mm, $nn);
$mm = $_;    # no warning
$mm = $nn;   # no warning

my $oo;
my @ary = ( 0, 1, 2, 3);
grep $ary[$_ ], @ary;  # no warning
grep $ary[$oo], @ary;  # warns

my $pp;
$pp = $ary[$_];   # warns

my $qq;
grep {$ary[$_ ]} @ary;  # no warning
grep {$ary[$oo]} @ary;  # warns