You can define your own logfile format :

Field Description Value (ex)
%host The name or IP of the remote host www.lyot.obspm.fr or 145.238.44.5
%date Date as Day:Hour or just Day 01/Jan/97:23:12:24 or 1998-02-02
%time Hour 23:12:24
%hourshift Shift from GMT +0200
%method Method requested to send the file GET
%page The file requested /index.html or /sky/astro.gif
%protocol Protocole used HTTP 1.0
%status The status code 200
%requetesize The byte transfered for the requested file 1345
%agent Browser and OS of the remote host Mozilla/4.01 (X11; I; SunOS 5.3 sun4m)
%referer The page the request come from http://www.google.com/
%virtualhost Name of the server the request was www.lyot.obspm.fr
%query Arguments from the request q=w3perl&meta=lr%3D%26hl%3Den
%direction FTP : outgoing or incoming transfer o
%I Input bandwith 56
%O Output bandwith 345
%transfert_time FTP : time to transfer 920
%elapsed Time to answer the request 120
%codestatus Proxy status code TCP_REFRESH_HIT/304
%peerstatus Proxy peer status DEFAULT_PARENT/127.0.0.1
%mimetype Proxy mimetype text/html
%id Mail log id B43F5744258
%module Mail log module sendmail
%message Mail log message a-pit@roll.com H=smtp.dom.com [38.113.3.61] P=esmtp S=15923
%null Anything not in this list ! -

For example, to get a CLF format, you should use :
%host %null %login %date %hourshift %method %page %protocol %status %requetesize