This program is a perl version of the most excellent shell scripted implementation written by Nigel Griffiths. The rewrite was just to address performance. The original implementation became quite consumptive for large files. As I was running it every 5 minutes through the day to give a semi-real-time view of performance, I needed something that would do so more efficiently.
Syntax is nmonchart.pl < /nmondata/`hostname`_`date +\%y\%m\%d`*.nmon > `date +\%Y-\%m-\%d`.html