I want to use sendmail to send me stuff and want to do it in a oneliner.

echo "mail content" | sendmail emailataddres.com 

Sends it without subject.

The subject line must come before the Mail content, so I am looking for something along the lines of:

echo "mail content" | prepend "Subject: All that matters" | sendmail emailataddres.com 

sed and awk tend to be really awkward to use and remember.

EDIT:Just to clarify: echo "Mail content" is just an illustrating example. I need to be able to prepend stuff to stdout streams from any source. e.g.: ifconfig, zcat, etc..