detect/set immutable on a file in Ruby - ruby

Question

I am in need of a ruby way to detect if immutable is set on a file. If it is I need to remove it. Make my change to the file and then return it to immutability. I have looked at File and Fileutils, I have searched but all I can find with immutable and ruby is how to make ruby objects and threads immutable, which is of course a different thing then what I am looking for. I am trying to avoid using the shell, I want to stick to ruby code if at all possible. I am imagining code something like this:
file_name = '/boot/grub2/grub.cfg'
was_immutable = false
if File.immutable?(file_name)
FileUtils.chattr '-i', file_name
was_immutable = true
end
#my changes
if was_immutable
FileUtils.chattr '+i', file_name
end

Answer 1

This might seem like an over-simplification, but you can probably see where it is going:
file_name = '/boot/grub2/grub.cfg'
a = %x[lsattr #{file_name}].chomp
puts a if a[/i/]
Ok, so based on the link in the comments below, here is what I could come up with as a ruby version (if a guru around, happy to see how this should look):
#!/usr/bin/env ruby
require 'fcntl'
FS_IOC_GETFLAGS = 0x80086601
EXT3_IMMUTABLE_FL = 0x00000010
$count = 0
def check(filename)
fd = IO.sysopen(filename, Fcntl::O_RDONLY)
f = IO.new(fd)
a = [0].pack("L_")
f.ioctl(FS_IOC_GETFLAGS, a)
unless a.unpack('L_')[0] & EXT3_IMMUTABLE_FL == 0
puts "#{filename} is immutable :- a[0] = #{a[0].to_s}"
$count += 1
end
f.close
end
ARGV.each do |arg|
Dir[arg + '/*'].each do |item|
check(item) if File.file?(item)
end
end
exit(1) unless $count == 0