Perl for Web Site Management

Using a BEGIN Block

Does that mean we’re stuck with putting the %month_num assignment up at the top of the script, such that it will be visible everywhere, not just in the subroutine where it’s needed? No, we’re not stuck with that. We can use a special trick to make part of our script execute immediately after the compilation phase, before the normal runtime stuff happens. That trick is to put that part of our script inside a block labeled with the special word BEGIN (in all caps).

Let’s modify that anonymous block enclosing the &get_seconds subroutine to be a BEGIN block, and move the %month_num hash definition from the top of the script to the inside of that BEGIN block. The final version of the &get_seconds subroutine, including its enclosing BEGIN block, will then look like this:

            BEGIN {
    my %date_seconds;
    my %month_num = (
        Jan => 0,
        Feb => 1, 
        Mar => 2,
        Apr => 3,
        May => 4,
        Jun => 5,
        Jul => 6,
        Aug => 7,
        Sep => 8,
        Oct => 9,
        Nov => 10,
        Dec => 11,
    ); sub get_seconds { # this subroutine accepts a date string of the form # '06/Jul/1999' and a time string of the form '12:14:00' # and returns the number of seconds since the Unix # epoch, as determined by Time::Local's timelocal # function. the subroutine caches conversions of the # date part in %date_seconds in order to improve # performance. my ($date, $time) = @_; my $seconds; if ($date_seconds{$date}) { $seconds = $date_seconds{$date}; } else { my ($day, $mon, $yr) = split /\//, $date; $mon = $month_num{$mon}; $yr = $yr - 1900; ...