matching only digits

From: Guruguhan \ N (Guruguhan.N_at_geind.ge.com)
Date: 06/28/04 

Date: Mon, 28 Jun 2004 19:47:12 +0530
To: <beginners@perl.org>

Hi All,
          I wanted to check whether the user input is only a number and does contain any alphabet/s anywhere i.e. starting, end or in-between. Can somebody tell me how to do this?

TIA

Guruguhan