Hi,

Reinventing the wheel can be a good way to learn. However, if you are in a rush, why not trying one of these:

GD::Graph::Histogram

http://search.cpan.org/~whizdog/GDGraph-histogram-1.1/lib/GD/Graph/histogram.pm

or

Perl Data Language (PDL) in connection with PGPLOT or PLplot.

Hope this helps