Question

I found this snippet of code I am having trouble trying to find a good way to exit the tail and move on to the next part of the script. Essentially I ant the first part to make a change for the person running the scripts, show log output using the below code, then move on to the next part of the script on user keypress. I cant get out of the tail without CTRL-C.

def do_tail( session, file )
  session.open_channel do |channel|
    channel.on_data do |ch, data|
      puts "[#{file}] -> #{data}"
    end
    channel.exec "tail -f #{file}"
  end
end

Net::SSH.start("server", "user", :keys => ["/user/.ssh/id_dsa"]) do |session|
  do_tail session, "/var/log/apache2/error.log"
  do_tail session, "/var/log/apache2/access.log"
  session.loop
end

UPDATE
The -f takes over I/O and makes it difficult to exit that ssh channel. I decided to move towards the suggestions and modify it. Here is the result in case someone else would like help on this topic.

require 'rubygems'
require 'net/ssh'

def exit?
        begin
                while input = STDIN.read_nonblock(1)
                return true if input == 'q'
                end
                false
                rescue Errno::EINTR
                false
                rescue Errno::EAGAIN
                false
                rescue EOFError
                true
        end
end

def do_tail( session, file )
        session.open_channel do |channel|
                channel.on_data do |ch, data|
                        puts "[#{file}]\n\n#{data}"
                end
                channel.exec "tail -n22 #{file}"
        end
end

def loggy
        iteration = 0
        loop do
                iteration = (iteration + 1)
                Net::SSH.start("server", "user", :keys => ["/user/.ssh/id_dsa"]) do |session|
                        do_tail session, "/var/log/apache2/error.log"
                end
                puts "\n\nType 'q' and <ENTER> to exit log stream when you are done!\n\n"
                sleep 5
        break if exit? or iteration == 3
        end
end

loggy

loop do
        puts "\nDo you need to view more of the log? (y/n)\n"
        confirm = gets.chomp
        if confirm =="y"
                loggy
        else
        end
        break if confirm == "n"
end
puts "Part Deaux!"

Answer 1

You’ve given the -f command line option to tail(1). That explicitly instructs tail(1) to exit when the user types ^C or otherwise kills the program. If you just want a specific amount of the file to be shown and not followed, then you might wish to use the -n command line option instead:

channel.exec "tail -n 24 #{file}"

24 will show roughly one terminal’s worth of data, though if your terminals are larger or smaller — or you’re interested in different amounts of data — then you might wish to tweak it further.

tail(1) is powerful; it’d be worth reading its documentation just in case there’s an even better way to do what you’re trying to accomplish.