A number of the alert parameters allow you to insert a variable which will be substituted for a value when the alert happens. Here is a list.
|$host||Host name (or IP address, if no name exists).|
|$hostip||The host IP address|
|$hostdnsname||The resolved DNS name for the host|
|$day||Current day of month|
|$date||Same as $year-$month-$day.|
|$time||The same as $hour$minute - note the absence of any punctuation - that's to make sure the file name is valid, if this mask is being used in a file name.|