uhg...

test.pl

use strict;
use warnings;

local $! = 100;
print '$! == ' . int($!) . "\n";

{
    local $! = $!; 

    print '$! == ' . int($!) . "\n";
    open( my $out, ">&STDOUT" ) or die "Can't dup STDOUT:  $!";
    print '$! == ' . int($!) . "\n";
    open( my $err, ">&STDERR" ) or die "Can't dup STDERR:  $!";
    print '$! == ' . int($!) . "\n";
}

print '$! == ' . int($!) . "\n";

__END__

$! == 100
$! == 0
$! == 29
$! == 29
$! == 0