gem 'systemd-journal', '~> 1.2.0'

require 'systemd/journal'

j = Systemd::Journal.new
j.seek(:tail)

# watch() does not return
j.watch do |entry|
  puts entry.message
end

j = Systemd::Journal.new

# only display entries from SSHD with priority 6.
j.filter(priority: 6, _exe: '/usr/bin/sshd')
j.each do |entry|
  puts entry.message
end

j = Systemd::Journal.new

j.seek(:head)   # move to the start of journal
j.move(10)      # move forward by 10 entries
c = j.cursor    # get a reference to this entry
j.move(-5)      # move back 5 entries
j.seek(c)       # move to the saved cursor
j.cursor?(c)    # verify that we're at the correct entry
j.seek(:tail)   # move to end of the journal
j.move_previous # move back
j.move_next     # move forward

j.current_entry # get the entry we're currently positioned at

# seek the entry that occured closest to this time
j.seek(Time.parse('2013-10-31T12:00:00+04:00:00'))

j = Systemd::Journal.new
j.seek(:tail)
# wait up to one second for something to happen
if j.wait(1_000_000)
  puts 'something changed!'
# same as above, but can be interrupted with Control+C.
if j.wait(1_000_000, select: true)
  puts 'something changed!'

j = Systemd::Journal.new
j.move_next
j.move_next until j.current_entry.catalog?

puts j.current_entry.catalog
# or if you have a message id:
puts Systemd::Journal.catalog_for(j.current_entry.message_id)

# write a simple message
Systemd::Journal.print(Systemd::Journal::LOG_INFO, 'Something happened')

# write custom fields
Systemd::Journal.message(
  message: 'Something bad happened',
  priority: Systemd::Journal::LOG_ERR,
  my_custom_field: 'foo was nil!'
)