Monitoring performance with time

       The time command is an excellent  tool  for analyzing the performance of a shell script or command. Simply type time followed by the command that you wish to time. Three results are printed when the program or script finishes executing: the actual length of time (real-world time spent on the program), the total time spent in the program, and the total time spent on CPU overhead. The first figure is perhaps the most useful, but the third figure will tell you how busy your CPU is.

Let us create a small shell script. Type in the following  lines to a text file named myscript.sh

 #!/bin/bash
 
   echo "Welcome to Unixlab "
 

       
Save the file and make it executable.

 $ chmod u+x  myscript.sh

Now run it  using time  

$ time myscript.sh

real 0m0.008s
user 0m0.004s
sys 0m0.000s

My machine is too fast to show any perceptible time.

Now try to expand the myscript.sh  by adding  a for loop as below 

 #!/bin/bash
for i in 1 2 3 4 5 
do
   echo "Welcome to Unixlab "
done

Run it 

$ time myscript.sh

 Welcome to Unixlab 
Welcome to Unixlab 
Welcome to Unixlab 
Welcome to Unixlab 
Welcome to Unixlab 

real 0m0.008s
user 0m0.004s
sys 0m0.004s

Still the real time is shown as 0.00.  Let us build a loop that takes a long

time to finish and see the difference.

 #!/bin/bash
x=1
while [ $x -le 100 ]
do
  echo "Welcome to Unixlab"
  x=$(( $x + 1 ))
done

Again run it.  I am getting the following  timings.

real 0m0.016s
user 0m0.012s
sys 0m0.004s 

   Please read the time man page regarding accuracy of  results and  other 

useful options.