bash pipe construct to prepend something to the stdoutput of previous command

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..

$ echo 1 | (echo 2 && cat)
2
1

I am pretty sure that there is a nicer solution, but this should do.

Either use what Claudius said or make your own:

~/bin/prepend:

#!/bin/sh
echo -en "$@"
cat -

e.g.:

$ echo "Splendid SUPANINJA! Let's do it!" |\
     prepend "Subject: Venetian Snares\n"

Subject: Venetian Snares
Splendid SUPANINJA! Lets do it!

This is inspired by Claudius answer.

If you don't want a break return between your outputs, add the -n param. This will look like:

$ echo 1 | (echo -n 2 && cat)

Which will give:

21

From the pieces I've gathered... you could do something like this:

echo "Subject: All that matters
`echo "mail content"`" | sendmail blah@blahblah

Notice that I did not close the quotes on the first line... because not all shells translate the \n into a newline character... but I have yet to find one that wont process an actual newline inside the quotes.

When a command is enclosed in the ` character, it will be executed and the output will be injected in-place. Keep in mind that this bit of code is a bit dangerous as it is possible to inject additional commands inline that could easily compromise your system...

****edit**** Following advise of Claudius, a cleaner option would look like this:

echo -e "Subject: All that matters \n $(echo "mail content") |sendmail blah@blahblah

Even with that template, it could be exploited.

You can prepend to piped output using process substitution:

$ echo "mail content" | cat <(echo "Subject: All that matters") -
Subject: All that matters
mail content