# Save some typing when you can!  Make your vars lexical where it makes sense.
my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime($tomorrows_time);

# Get the last two digits.  Much cleaner and faster
$year = substr($year,-2,2); 

# I like to use a variable to turn on/off the debug code
my $debug = 1; # somewhere near the top
print "Testing: $important_currencies{$abbrev}" if $debug;

# It's SO EASY to check for a zero in your divisor, so don't pass up the free ride!  :) 
my $newrate;
if (!$second_currency) {
  print "HEY!  Don't divide!  You'll puke!\n";
}
else {
  $newrate = ($first_currency / $second_currency);
}