Report the first 10 lines of all files on the command line, transparently decompressing .xz compressed files.

logreport.rb

#!/usr/bin/ruby
# encoding: UTF-8

# The audit team wanted to know that we were doing logging as required. As
# evidence, they asked for a regular report consisting of the first 10 lines
# of each daily log file. I wrote this script to automate the process.
# If you want the last 10 lines instead, I suggest the Ruby Gem called Elif,
# which wraps any IO object to read line by line backwards.

LINES_OF_LOG = 10
XZCAT = '/usr/bin/xzcat --decompress --stdout'

def firstlines(filename, numlines)
  stream = nil
  pathname = File.realpath(filename)
  result = "### #{pathname} ###\n\n"
  if filename.match('.xz')
    stream = IO.popen("#{XZCAT} #{filename}")
  else
    stream = File.open(filename, "r")
  end
  gotone = false
  for i in 1..numlines
    line = stream.gets
    if line
      gotone = true
      result << line
    end
  end
  if !gotone
    result << "[No text in log file #{pathname}]\n"
  end
  return result << "\n"
end

if ARGV.length == 0
  puts "#{$0} [FILE] ..."
  puts "   Outputs a report listing the first #{LINES_OF_LOG} lines from each listed file."
  puts "   Transparently decompresses files compressed with xz."
end

for file in ARGV
  puts firstlines(file, LINES_OF_LOG)
end