If you're only looking for one possibility and want to stay mostly in the shell rather than using awk or perl, you could do something like:
tail -F /path/to/serverLog | grep --line-buffered 'server is up' | while read ; do my_command ; done
...which will run
my_command every time "server is up" appears in the log file. For multiple possibilities, you could maybe drop the
grep and instead use a
case within the
tail to watch for the log file to be rotated; i.e. if the current file gets renamed and another file with the same name takes its place,
tail will switch over to the new file.
--line-buffered option tells
grep to flush its buffer after every line; otherwise,
my_command may not be reached in a timely fashion (assuming the logs have reasonably sized lines).