This shell script monitors and calculates CPU usages for one hour:

#!/bin/bash
#Name: pcpu_usage.sh
#Description: Script to calculate cpu usage by processes for 1 hour

#Change the SECS to total seconds to monitor CPU usage.
#UNIT_TIME is the interval in seconds between each sampling

SECS=3600
UNIT_TIME=60

STEPS=$(( $SECS / $UNIT_TIME ))

echo Watching CPU usage... ;

# Collect data in temp file

for((i=0;i<STEPS;i++))
do
  ps -eocomm,pcpu | egrep -v '(0.0)|(%CPU)' >> /tmp/cpu_usage.$$
  sleep $UNIT_TIME
done

# Process collected data
echo
echo CPU eaters :

cat /tmp/cpu_usage.$$ | \
awk '
{ process[$1]+=$2; }
END{ 
  for(i in process)
  {
    printf("%-20s %s\n",i, process[i]) ;
  }

   }' | sort -nrk 2 | head

#Remove the temporary log file
rm /tmp/cpu_usage.$$

The output resembles the following:

$ ./pcpu_usage.sh
Watching CPU usage...
CPU eaters :
Xorg        20
firefox-bin   15
bash        3
evince      2
pulseaudio    1.0
pcpu.sh         0.3
wpa_supplicant  0
wnck-applet     0
watchdog/0      0
usb-storage     0