Oneliner to send email with attachment using sendmail:

$S Subject
$B Body
$A Attachment

S="Subject"; B="Body goes here.";A=/tmp/file.zip;Y=B_$;(echo -e "From: $USER@$HOSTNAME\nSubject: $S\nMIME-Version: 1.0\nContent-Type: multipart/mixed; boundary=\"$Y\";\n--$Y\nContent-Type: text/plain\n\n$B\n--$Y\nContent-Type: application/octet-stream;\nContent-Disposition: attachment; filename=\"`echo $A|sed s@/tmp/@@`\"\nContent-Transfer-Encoding: base64\n";openssl base64 -e < $A;echo "--$Y--") | sendmail mail@host.com