Running a shell command on a buffer?

[drevil]

I have a question about our favorite editor/browser/operating-system.
An increasing number of doofuses are starting to send me html-encoded
email.  I wish I could tell them to all not do that (rmail doesn't
handle html), but I'll be fighting a losing battle.

So, I would like to set up rmail in such a way that I can quickly
de-htmlify a buffer.  There are plenty of shell commands (like the
dehtml.awk script) which will strip out html, but I can't figure out
how to get emacs to use them.

The way it would work is this: I use a command (M-x dehtml or
something) and it sends the entire contents of the current buffer to
the stdin of this shell script, and then replaces the entire contents
of the buffer with the output of the shellscript, and then lets me
save it in the rmail file.

Is there an easy way to do this?

Or should I just get myself to use VM?

Thanks for your help