Beginning of /etc/dhclient.conf file:

# Configuration file for /sbin/dhclient, which is included in Debian's
#       dhcp3-client package.
#
# This is a sample configuration file for dhclient. See dhclient.conf's
#       man page for more information about the syntax of this file
#       and a more comprehensive list of the parameters understood by
#       dhclient.
#
# Normally, if the DHCP server provides reasonable information and does
#       not leave anything out (like the domain name, for example), then
#       few changes must be made to this file, if any.
#

#send host-name "andare.fugue.com";
#send dhcp-client-identifier 1:0:a0:24:ab:fb:9c;
#send dhcp-lease-time 3600;
#supersede domain-name "fugue.com home.vix.com";
prepend search bar;
#prepend domain-name-servers 127.0.0.1;
request subnet-mask, broadcast-address, time-offset, routers,
        domain-name, domain-name-servers, host-name,
        netbios-name-servers, netbios-scope, interface-mtu;
#require subnet-mask, domain-name-servers;


#######
Errors when trying to use (note that I didn't touch line 20...) :


jthomas@jthomas:~$ sudo dhclient eth0
There is already a pid file /var/run/dhclient.pid with pid 11230
killed old client process, removed PID file
Internet Systems Consortium DHCP Client V3.0.6
Copyright 2004-2007 Internet Systems Consortium.
All rights reserved.
For info, please visit http://www.isc.org/sw/dhcp/

/etc/dhcp3/dhclient.conf line 18: no option named search
prepend search bar;
        ^
/etc/dhcp3/dhclient.conf line 20: semicolon expected.
request
^
Listening on LPF/eth0/00:0b:db:4c:a5:21
Sending on   LPF/eth0/00:0b:db:4c:a5:21
Sending on   Socket/fallback
DHCPREQUEST on eth0 to 255.255.255.255 port 67
DHCPACK from 10.10.13.1
bound to 10.10.13.173 -- renewal in 122426 seconds.
jthomas@jthomas:~$