How to configure `eth0` to retry `dhclient` when unplugged and replugged?

I'm working on a linux gadget.

I want it to get DHCP if I plug in the network cable after it has booted up already or if the network cable unplugged and replugged.

One solution is to run a script such as this (which works, btw):

#!/bin/bash

NET_STATUS='different'

while true
do
  NEW_NET_STATUS=`ifconfig | grep RUNNING | grep -v LOOPBACK`
  if [ "${NEW_NET_STATUS}" = "${NET_STATUS}" ]
  then
    echo "no change"
    sleep 1
    continue
  fi
  NET_STATUS=${NEW_NET_STATUS}
  if [ "${NET_STATUS}" ]
  then
    echo "cable plugged in"
  else
    echo "cable unplugged"
  fi
  sleep 1
done

However, I've got a feeling deep down in my little toe that tells me that there's a better way to deal with hotplug events for the ethernet cable.

netplug

netplug is the solution that I went with. ifplugd may work just as well.

Installation

sudo apt-get install netplug

Interface Configuration

cat /etc/netplug/netplugd.conf
eth*

Event Configuration

cat /etc/netplug/netplug
#!/bin/sh
PATH=/usr/bin:/bin:/usr/sbin:/sbin
export PATH

dev="$1"
action="$2"

case "$action" in
in)
    echo "$dev : $action : plugged in" >> /tmp/netplug.log
    ;;
out)
    echo "$dev : $action : unplugged" >> /tmp/netplug.log
    ;;
probe)
    echo "$dev : $action : probed" >> /tmp/netplug.log
    ;;
*)
    echo "$dev : $action : I feel violated" >> /tmp/netplug.log
    exit 1
    ;;
esac

Testing

/etc/init.d/netplug stop
/etc/init.d/netplug start

cat /tmp/netplug.log
eth0 : probe : probed
eth1 : probe : probed
...
eth15 : probe : probed
eth0 : in : plugged in

ifplugd handles this situation very well:

ifplugd is a Linux daemon which will automatically configure your ethernet device when a cable is plugged in and automatically unconfigure it if the cable is pulled. This is useful on laptops with onboard network adapters, since it will only configure the interface when a cable is really connected.

ifplugd interfaces with your distribution's native network configuration utilities.

Some features:

Uses your distribution's native ifup/ifdown programs.

[...]

Supports the Linux SIOCETHTOOL (newer, aka ethtool API), SIOCGMIIREG (older, aka mii-diag/mii-tool API) and SIOCDEVPRIVATE (oldest, aka mii-tool API) ioctl()s for getting link status. Release 0.24 introduces support for link detection with the IFF_RUNNING interface flag.

[...]

Can be configured to ignore short "unplugged" periods (-d option) or short "plugged" periods(-u option)

[...]

Compatibility mode for network devices which do not support cable detection (-F option)