Sometimes it is interesting to see how long a program took to run. This is usefull to see how long a backup took to be complete, how long you surfed the net, or many other things.

This is taken from one of my posts to a mailing-list I used to subscribe:

stw@laptop:~> date ; echo This line intentionally left blank ; sleep 5 ; date
Sa Jun 18 20:47:59 CEST 2005
This line intentionally left blank
Sa Jun 18 20:48:04 CEST 2005

which will tell you start and end of the run of the program (tar, netscape, whatever). You have to do the math on your own.

'time' does this:

stw@laptop:~> time sleep 5
 
real    0m5.066s
user    0m0.002s
sys     0m0.002s

So we know how long the nap really was, and how much time the CPU spent to run the sleep-application. The drawback is that 'time' only times one command. So if you want to time pipes or multiple commands that run after each other, you need to put them into a script and time that script, or use 'date' and do the math… :(