logwarn searches for interesting messages in log files, where
interest- ing'' is defined by an user-supplied list of positive and negative (pre- ceeded with a!'') extended regular expressions provided on the command
Each log message is compared against each pattern in the order given. If
the log message matches a positive pattern before matching a negative
!pattern then it's printed to standard output.
logwarn keeps track of its position between invocations, so each matching
line is only ever output once. It also finds messages in log files that
have been rotated (and possibly compressed) since the previous invoca-
logwarn also includes support for log messages that span multiple lines.