Perl5 リファレンス

       sleep EXPR

       sleep   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

               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 the select entry elsewhere in this document
               above.  The Time::HiRes module from CPAN may also

               See also the POSIX module's `sigpause' function.