logalert is a log file monitor tool which executes
a specific action whenever it matches a string
(pattern) occurrence. It reads an entire file (or
starts at the end, just like tail -f) and keeps
track of any changes, waiting for a specific
pattern (a syslog process error, a user login,
etc.) and starting an action you define when it
finds it. It uses regular expressions to match the
pattern occurrence and executes commands via shell
interaction. It deals with the log rotation and
temporary removals normally used by sysadmins.