Port statistics on Cisco switch

In the "show interface" output, you'll see cumulative counters since the last counter reset ("clear counters []", no specified interface clears counters for all interfaces). This allows you to take snapshots at whatever interval you want. It's the same counters as used by the SNMP management interface (Cacti, MRTG and other monitoring software) and should be relatively easy to parse.

If you're happy scraping the CLI output and do it yourself, that MAY be a quicker way to get up and running with this specific task. I do suspect that some training material and time to install MRTG or Cacti will be worth your time investment, though.

To make this easy for yourself (and show off some pretty graphs), I'd just install Cacti and use SNMP to monitor the switch ports.