Causes the script to sleep for n
seconds, or forever if no argument is given. It may be
interrupted by sending the process a
SIGALRM. The function
returns the number of seconds actually slept. On some systems, the function
sleeps till the "top of the second," so, for instance, a
1 may sleep anywhere from 0 to 1 second, depending on when in the
current second you started sleeping.