preg_match help please

Hi I am trying to find a regular expression to match a variable, what I think should work (but doesn't) is; preg_match ('^/[\w],[\w],/', $variable) The $variable MUST contain an alpha-numeric string, followed by a comma, followed by another alpha-numeric string, followed by another comma followed by (but doesn't have to!!) another alpha-numeric string followed by nothing. I realise my regex above doesn't allow for the last 'followed by nothing', but to me it looks like it should match the first part of the string up to the last comma? Help appreciated, and apologies if this isn't strictly the correct group. Thanks Steve