Track CPU usage Top 10 over time

#!/bin/bash
# --- Version history ---
# track cpu usage all the time. $1 is logfile name.
# --- Version history ---
# Usage: cputrack [PID] [filename]
#        replace [PID] with process ID #
#        replace [filename] with base file name to use (no extension)
filepath=/Users/ialaddin   # modify as desired
interval=20                         # reports per minute
timelimit=6000                      # how long to run, in seconds
mydate=`date "+%H:%M:%S"`           # the timestamp
freq=$((60/$interval))              # for sleep function
while [ "$SECONDS" -le "$timelimit" ] ; do
  ps ax -opcpu -ocomm | sort -nrk 3,3 | head -n 10 | sed "s/^/$mydate /" >> $filepath/$1.txt
  sleep 3
  mydate=`date "+%H:%M:%S"`
done