Writing commands to send notifications

Another part of Nagios that can be extended to fit your needs are notifications. These are messages that Nagios sends out whenever a problem occurs or is resolved.

One way in which Nagios' notification system can be expanded is to create template-based e-mails. These will send notifications as both plain text and HTML messages. The template of the e-mail will be kept in separate files.

We will use Tcl for this purpose as it contains libraries for MIME (http://tcllib.sourceforge.net/doc/mime.html) and SMTP (http://tcllib.sourceforge.net/doc/smtp.html) functionality. The first one allows the creation of structured e-mails, whereas the latter one is used to send these using an SMTP server.

E-mails that contain content in multiple formats need to be wrapped in the multipart/alternative MIME type. This type will contain two subparts: first the plain text version and then the HTML version. This order makes e-mail clients choose HTML over plain text if both the...