Sample the CPU Load and Memory usage of an application over time and returns the average, standard deviation and min-max range.

ps_avg.rb

# Sample the CPU Load and Memory usage of an application over time and 
# returns the average, standard deviation and min-max range.

# processname to check as $1, number of samples as $2
# eg: ruby ps_avg.rb safari 100
process_name = ARGV[0]
sample_count = ARGV[1] || 120
samples_per_seconds = 3
sleep_time = (1/samples_per_seconds.to_f)

puts "Sampling: #{process_name}, taking #{sample_count} samples (#{samples_per_seconds} per second)"

## Expand the Enumerable module with Basic statistics
module Enumerable
  #  sum of an array of numbers
  def sum
    return self.inject(0){|acc,i|acc +i}
  end
  
  #  average of an array of numbers
  def average
    return self.sum/self.length.to_f
  end
  #  variance of an array of numbers
  def sample_variance
    avg=self.average
    sum=self.inject(0){|acc,i|acc +(i-avg)**2}
    return(1/self.length.to_f*sum)
  end
  #  standard deviation of an array of numbers
  def standard_deviation
    return Math.sqrt(self.sample_variance)
  end
end  
## close module Enumerable

## Print floats with 2 decimals
class Float
  def to_s
    sprintf("%.2f", self)
  end
end

## Method that does the fetching of cpu load and mem usage
## Tested on MacOS X and FreeBSD. The regexp might need tweaking for Linux
def get_cpu_and_mem(pname)
  output = `ps uxa`
  regexp = /[a-z]+\s+[0-9]+\s+([0-9,\.]+)\s+[0-9,\.]+\s+\d+\s+(\d+)/
  lines = output.split("\n").select{ |x| x.downcase.include?(pname.downcase) && !x.include?("ruby") }
  lines.collect do |line|
    line.scan(regexp).first.collect{ |x| x.gsub(',','.').to_f }
  end.inject([0,0]){ |x,sum| [x[0] + sum[0],x[1] + sum[1]] }
end

## Loop for sample_count times and gather the samples in the samples array
samples = {:cpu => [], :mem => []}
sample_count.to_i.times do 
  cpu, mem = get_cpu_and_mem(process_name)
  samples[:cpu] << cpu
  samples[:mem] << mem/1024.0
  sleep sleep_time
end

def print_stats(array,name)
  print "Average #{name}: #{array.average}\t"
  print "StdDev: #{array.standard_deviation}\t"
  puts "Range: #{array.min} - #{array.max}"
end

print_stats(samples[:cpu],"cpu load (%)")
print_stats(samples[:mem],"mem use (MB)")