Returns the number of non-leap seconds since whatever time the system considers to be the epoch (that's 00:00:00, January 1, 1904 for Mac OS, and 00:00:00 UTC, January 1, 1970 for most other systems). Suitable for feeding to gmtime and localtime.
For measuring time in better granularity than one second, you may use either the Time::HiRes module (from CPAN, and starting from Perl 5.8 part of the standard distribution), or if you have gettimeofday(2), you may be able to use the syscall interface of Perl. See perlfaq8 for details.