Script that limits application CPU usage on OSX

cpu_limiter.sh

#!/bin/bash

#########################
# CPU LIMITER (for OSX) #
#########################

<<DESCRIPTION
	The script limits an application CPU usage.
	-------------------------------------------
	You have to specify application PID (process id) and desired CPU usage percentage.
	The script is a big while loop that 
		(1) sends SIGSTOP signal to the appication
		(2) sleeps X millisecond
		(3) sends SIGCONT signal.
	Sleeping time gets bigger  ( X += 0.01 ) when actual CPU usage is over the limit
	Sleeping time gets smaller ( X -= 0.005) when actual CPU usage is under the limit
	This way the average CPU usage hovers around the desired percentage.
DESCRIPTION

<<USAGE
	(1) sudo chmod +x cpu_limiter.sh
	(2) Run 'top' from terminal to see application PIDs
	Script works with 2 parameter:
	- pid of the application what you want to limit
	- cpu usage limit in percents (0-100) 
	
	Example
		cpu_limiter.sh 1234 20
	This limits the application with 1234 PID to 20% CPU 
USAGE

<<CREATOR
	Lorand Horvath, email at hlorand.hu, 2015
CREATOR

########################################################################################### 

# PARAMETERS
PID=$1
PERCENT=$2

# INITIAL SLEEPTIME
SLEEPTIME=0

while true
do
	# THE HEART OF THE SCRIPT
	# -----------------------
	kill -SIGSTOP $PID &
	sleep $SLEEPTIME
	kill -SIGCONT $PID &

	# CPU USAGE OF THE APPLICATION
	# ----------------------------
	# ps prints only the cpu% of the app, tail gets only the last line
	# tr and awk filters out comma and space to get integer part
	CPUUSAGE=$(ps -p $PID -o %cpu | tail -1 | tr -d ' ' | tr ',' ' ' | awk '{print $1}')
	#CPUUSAGE=$(ps -p $PID -o %cpu | tail -1 | tr -d ' ' | tr ',' '.')

	#DIFFERENCE=$( echo '(' $CPUUSAGE '-' $PERCENT ') / 1000' | bc -l )

	# CALIBRATING SLEEP TIME
	# ----------------------
	# If actual CPU usage is smaller than the limit, slowly decrease sleep time
	if [ $( echo $CPUUSAGE '<' $PERCENT  | bc ) -eq 1 ]; then
		if [ $( echo $SLEEPTIME '<0.00001' | bc ) -eq 0 ]; then
               		SLEEPTIME=$( echo $SLEEPTIME ' - 0.005' | bc -l)
		fi
	fi

	# If actual CPU usage is bigger than the limit, increase sleep time
        if [ $( echo $CPUUSAGE '>' $PERCENT  | bc ) -eq 1 ]; then
		if [ $( echo $SLEEPTIME '>0.5' | bc ) -eq 0 ]; then
	       		SLEEPTIME=$( echo $SLEEPTIME ' + 0.01' | bc -l)
        	fi
	fi

	# debug info
	echo $SLEEPTIME $CPUUSAGE

done