Block for some number of seconds
Causes the script to sleep for EXPR seconds, or forever if no EXPR.
May be interrupted if the process receives a signal such as
SIGALRM. Returns the number of seconds
actually slept. You probably cannot mix alarm() and sleep() calls,
because sleep() is often implemented using alarm().
On some older systems, it may sleep up to a full second less than what you requested, depending on how it counts
seconds. Most modern systems always sleep the full amount. They may appear to sleep longer than that, however,
because your process might not be scheduled right away in a busy multitasking system.
For delays of finer granularity than one second, you may use Perl's syscall() interface
setitimer(2) if your system supports it, or else see select()
See also the POSIX module's