use MIME::Lite;

$m = MIME::Lite->new;
$m->build(
    from => 'me',
    to   => 'you',
    Data => '',
    subject => 'Foo Bar',
);
$m->attach(
    Type    => 'text/plain',
    Data    => 'this is an attachment'
);
$m->print;
__END__
Content-Transfer-Encoding: 7bit
Content-Type: multipart/mixed; boundary="_----------=_150137533476690"
MIME-Version: 1.0
Date: Sun, 30 Jul 2017 02:42:14 +0200
From: me
To: you
Subject: Foo Bar
X-Mailer: MIME::Lite 3.030 (F2.85; T2.09; A2.13; B3.14; Q3.13)

This is a multi-part message in MIME format.

--_----------=_150137533476690
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
Content-Type: text/plain


--_----------=_150137533476690
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
Content-Type: text/plain

this is an attachment
--_----------=_150137533476690--