This is a recursive way to do it but it gets slow quickly for larger values unless you memoze it.

print "$_ : ", fibo($_), "\n" for 0..23;

sub fibo{
    my $n = shift;
    if ( $n == 0){ return 0;}
    elsif( $n == 1){ return 1;}
    else { return fibo($n-1) + fibo($n-2);}
}
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