sub doit
{
 my @array = qw(1 2 3 4);
 # this doesn't damage outer @array:
 $_ = 'xyz' foreach (@array);
}

my @array = qw(a b c d);
print join("|", @array), "\n";

foreach (@array)
{
 my $f = doit('abcd');
}

print join("|", @array), "\n";
[download]

Try the following with and without the 'local $_;' line and you'll see what he's talking about.

use strict;

sub getfile {
local $_;
    my $filename = shift;
    local *F;
    open F, "< $filename" or die "Couldn't open `$filename': $!";
    my $contents;
    while (<F>) {
      s/#.*//;              # Remove comments
      next unless /\S/;     # Skip blank lines
      $contents .= $_;      # Save current (nonblank) line
    }
    return $contents;
}

my @array = ("base_tester", "Foo.pm");
foreach (@array) {
  my $filename = $_;
  my $f = getfile($filename);
}

print "@array\n";
[download]

That's what I tried to see the effects, and I was rather surprised.

No, while(<>) does not create a newly scoped $_.

Behold:

require 5.6.1;
use strict;
use warnings;

my @array= (1,2,3,4,5);
foo()  foreach  (@array);
print "@array\n";

sub foo
 {
 while (<DATA>) { return }
 # silly, but makes a small example with little input.
 }

__DATA__
clobbered
clobbered
clobbered
clobbered
clobbered
[download]