1. Update, I was wrong, 0 is sunday, source: perldoc
2. Else if you run it on an unix system you can always use a cronjob it might be easier from an administration point of view
3. Added the usual disclaimer at end of post

Funny you should ask that, for a script at work I just started using Date::Calc for manipulating weekdays, if you just want that datum and nothing else you can get it using this:

my $wday = (localtime)[6];
if($wday == 0 || $wday == 6){
#do something
}
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Be aware that its only my kind of fishing here, keep looking for answers and explanations.