Periodically send new lines in log file to specified email address.

tail-n-mail.rb

# Script to periodically send new lines in log file to specified mail address.
# 
# Similar to http://bucardo.org/wiki/Tail_n_mail - but I needed
# substitution to handle newlines in Python-generated messages, and it
# was faster to homebrew my own script than to add features to an
# already overfeatured Perl script.  And I want to practice Ruby - seems
# to be fine for small, one-off scripts.
# 
# License: WTFPL or MIT, whichever you prefer.

require 'net/smtp'
require 'yaml'

DEFAULT_CONFIG = {
  'file' => '/var/log/FIXME',
  'offset' => 0,
  'mailto' => 'FIXME@example.com',
  'mailfrom' => 'FIXME@example.com',
  'subject' => 'Logged messages',
  'FIXME' => "Remove this line from config to notify script you've actually configured anything.",
}

unless File.exists? ARGV[0]
  File.open ARGV[0], 'w' do |f|
    f.puts YAML::dump(DEFAULT_CONFIG)
  end
  exit
end

$conf = YAML::load_file ARGV[0]
abort "Please configure #{ARGV[0]} and remove the FIXME line."  if $conf['FIXME']

content = ''
File.open $conf['file'] do |f|
  f.seek $conf['offset']
  content = f.read
  $conf['offset'] = f.tell
end

$conf['substitute'].each do |key, value|
  content.gsub! key, value
end

unless content.empty?
  Net::SMTP.start('localhost') do |smtp|
    smtp.send_message <<MESSAGE, $conf['mailfrom'], $conf['mailto']
From: <#{$conf['mailfrom']}>
To: <#{$conf['mailto']}>
Subject: #{$conf['subject']}

#{content}
MESSAGE
  end
end

File.open ARGV[0]+'+', 'w' do |f|
  f.puts YAML::dump($conf)
end
File.rename ARGV[0], ARGV[0]+'~'
File.rename ARGV[0]+'+', ARGV[0]