Communication: Humans Talk. Computers Talk - Smart Home Automation with Linux and Raspberry Pi - page 153

which can be called with this:
xmitemail "Hello" " [e-mail] " "I bet you didn't think this would work!"
This command will send the simplistic e-mail shown and can be either invoked by typing it on the command
line triggering it from a daily crontab or run as a consequence of some other household event. For example, someone
coming through the front door (using the Arduino door mat from Chapter 2) could issue such as e-mail, or it could be
sent as a warning when one of the hard disks get too full.
I have subverted the original interface to mail here, because it will be more usual for users to invoke the command
in the manner shown earlier. However, there will be times when you want to revert to the original usage of mail by
allowing the script to accept any input from STDIN. This requires the three-line replacement shown here to usurp MSG:
if [ $# -eq 0 ]; then
while read LINE ; do
MSG="$MSG""^M""$LINE"
done
else
MSG=$*
fi
Note the ^M character, which is entered into editors like vi with Ctrl+V followed by Ctrl+M. Now the message can
now be fed in from a file, like this:
cat filename | xmitemail "Here's the file" " [e-mail] "
In Chapter 7, you'll learn how to extend this functionality to support a basic address book and multiple receivers.
Autoprocessing E-mails
Accepting e-mails on behalf of a program, instead of a human user, can be summed up in one word: Procmail. 4
Procmail was a project begun in 1990 by Stephen R. van den Berg to control the delivery of e-mail messages, and
although some consider it a dead project, this makes it a stable project and one that's unlikely to break or introduce
new complications any time soon!
Procmail is triggered by the e-mail server (an MTA, such as Exim) by passing each message for further processing
to each of a series of recipes . If none of these recipes lays claim to the message, it is delivered as normal.
I'll begin by creating a simple example whereby you can e-mail your bedroom light switch. So, create a user with
the following, and fill in all the necessary user details:
adduser bedroom
Then, create a .procmailrc file (note the dot!) in their home directory, and add the following recipe code:
:0
* ^From steev
* ^Subject: light on
|heyu turn bedroom_light on
)NTHEINTERESTSOFOBJECTIVENESS)ȀLLALSOADMITTHAT maildrop AND dovecat EXISTANDPERFORMSIMILARTASKS