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 to access setitimer(2) if your system supports it, or else see "select" above. The Time::HiRes module (from CPAN, and starting from Perl 5.8 part of the standard distribution) may also help.
See also the POSIX module's pause function.