Programming Perl, 4th Edition

sleep

sleep EXPR
sleep

This function causes the script to sleep for EXPR (integer) seconds, or forever if no EXPR, and returns the number of seconds slept. It may be interrupted by sending the process a SIGALRM. 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, the standard Time::HiRes module provides a usleep function. If available, the select (ready file descriptors) call can also give you better resolution. You may be able to use syscall to call the getitimer(2) and setitimer(2) routines that some Unix systems support. You probably cannot mix alarm and sleep calls because sleep is often implemented using alarm.

See also the POSIX module’s pause function.