How can I read stderr when a command execution fails in Perl?

my @lines = `/usr/local/bin/diff -udr "$expected_file" "$gen_file"`;

if ($? != 0)
{
    print ERRFILE "Diff between $expected_file and $gen_file failedn";
    return $diff_err;
}

use IO::CaptureOutput 'qxx';


my ($stdout, $stderr, $ok) =
    qxx( qq(/usr/local/bin/diff -udr "$expected_file" "$gen_file") );

if (! $ok)
{
    print ERRFILE "Diff between $expected_file and $gen_file failedn";
    return $stderr;
}

my @lines = split /n/, $stdout;