OO to the rescue:

use strict;

my $bool = TrueOnce->new();

print $bool->value(), "\n" for (0..4);

package TrueOnce;

sub new { bless { true=>1 }, shift }

sub value {
   my $self = shift;
   my $val  = $self->{'true'};
   $self->{'true'} = 0;
   return $val;
}
[download]

UPDATE: /me smacks forehead
Do what Rhandom said. Sometimes finding the solution to a probably is not as good as solving the RIGHT PROBLEM. Rhandom++

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
F--F--F--F--F--F--F--F--
(the triplet paradiddle)