Watch/read a growing log file

Question

I have a log file that is constantly growing. How can I watch and parse it via a Ruby script?

The script will parse each new line as it is written to the file and ou

Answer 1

You can use Kernel#select in the following way:

def watch_for(file,pattern)
   f = File.open(file,"r")

   # Since this file exists and is growing, seek to the end of the most recent entry
   f.seek(0,IO::SEEK_END)

   while true
      select([f])
      puts "Found it!" if f.gets =~ pattern
   end
end

Then call it like:

watch_for("some_file", /ERROR/)

I've elided all error checking and such - you will want to have that and probably some mechanism to break out of the loop. But the basic idea is there.