gistfile1.rb

require 'bigdecimal'
#Set values to determine output based on how much % of memory is free
CRITICAL=5
WARNING=10
File.open "/proc/meminfo","r" do |line|
  @memtotal = BigDecimal.new($1) if line.gets =~ /MemTotal:\s+(\d+)\s+kB/
  @memfree = BigDecimal.new($1) if line.gets =~ /MemFree:\s+(\d+)\s+kB/
end
if @memtotal and @memfree
  @free_percentage = ((@memfree/@memtotal)*100)
  case @free_percentage.to_i
  when 0..CRITICAL
    print "CRITICAL - Only #{@free_percentage.to_i}% free memory!"
    exit 2
  when CRITICAL..WARNING
    print "WARNING - Only #{@free_percentage.to_i}% free memory!"
    exit 1
  else
    print "OK - #{@free_percentage.to_i}% free memory"
    exit 0
  end
else
  print "UNKNOWN - Cannot get free memory!!!"
  exit 3
end