I use wireless in Tinycore, while dont wanna to install wireless_tools, KISS...
I changed the line of /etc/init.d/dhcp.sh as below, and does it works!
Just for your reference.
#!/bin/sh
# The DHCP portion is now separated out, in order to not slow the boot down
# only to wait for slow network cards
. /etc/init.d/tc-functions
# This waits until all devices have registered
/sbin/udevsettle
#NETDEVICES="$(awk -F: '/eth.:|tr.:/{print $1}' /proc/net/dev 2>/dev/null)" get the interface, really waste of time
for DEVICE in eth[0-9] wlan[0-9] ath[0-9]; do
echo "${GREEN}Network device ${MAGENTA}$DEVICE${GREEN} detected, DHCP broadcasting for IP.${NORMAL}"
trap 2 3 11
/sbin/udhcpc -b -i $DEVICE -h $(/bin/hostname) -p /var/run/udhcpc.$DEVICE.pid >/dev/null 2>&1 &
trap "" 2 3 11
sleep 1
done