If the date is in YYYY-MM-DD format, then a simple string comparison works fine

  my @dates = qw( 2001-12-24 1999-03-2 2004-04-23 );
  print join(', ', sort { $b cmp $a } @dates );
[download]

prints

  2004-04-23, 2001-12-24, 1999-03-2
[download]

The whole thing is much simpler if you use grep. In fact, you can find, and set the 'isnext' key in a single line. What you want to find is the smallest date larger than or equal to the given date. First sort the dates in ascending order:

sort { $a->{date} cmp $b->{date} } @$array
[download]

then grep out those that are larger than the given date:

grep { $_->{date} ge $today } ...
[download]

and the first one of those will be your match:

 ( ... )[0]->{isnext} = 1;
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So the answer goes like this:

(grep {$_->{date} ge $today} sort {$a->{date}cmp $b->{date} } @$array)
+[0]->{isnext} = 1;
[download]

The whole thing then looks like this:

my $today = '2001-03-28';
my $array = [
  { date => '2001-02-01' },
  { date => '1999-04-09' },
  { date => '2001-03-31' }, 
  { date => '2001-03-24' },
  { date => '2001-04-15' },
];


# find the smallest date larger than or equal to today.

# set the isnext flag 
(grep { $_->{date} ge $today } sort { $a->{date} cmp $b->{date} }  @$a
+rray)[0]->{isnext} = 1;

# print all out and indicate which one is next...
for my $e (@$array) {
  print "\n", $e->{date};
  print " this is next" if $e->{isnext};
}

# alternatively : 
my $thenext = (grep { $_->{date} ge $today } sort { $a->{date} cmp $b-
+>{date} }  @$array)[0];
print "\nThe next date is: $thenext->{date}\n";
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