send mail with attachment in command line

if it is a normal text file, you can use redirection to send the file as
content:

mail -s "hello, david" someone@abc.com someone2@kseeker.com < attachfile

if it is a binary file, or you want to send text file as real attachment:

mail -s "hello, david" -a attachfile someone@abc.com someone2@kseeker.com

btw, mail is often the alias of mailx command in linux.