CraftBukkit updater - Set your directory and desired version (recommended build, beta or development) and run this script. The latest build will downloaded and previous will be kept in your directory. For running a server, you can use symbolic link craftbukkit.jar which is always pointing to the newest build (highest version number).

craftbukkit_update.sh

#!/bin/sh
basedir="/opt/minecraft/bukkit"
RB="http://dl.bukkit.org/downloads/craftbukkit/get/latest-rb/craftbukkit.jar"
BETA="http://dl.bukkit.org/downloads/craftbukkit/get/latest-beta/craftbukkit.jar"
DEV="http://dl.bukkit.org/downloads/craftbukkit/get/latest-dev/craftbukkit.jar"

# Choose desired version: RB, BETA, DEV
DOWNLOAD=$BETA

#####################################################

function removeSymlinks {
    result=""
    for var in "$@"; do
        [ -L $var ] || result="$result$var "
    done
    echo $result
}

function findMax {
    max=$1
    for var in "$@"; do
        nvar=`echo $var|sed 's/[^0-9]*//g'`
        nmax=`echo $max|sed 's/[^0-9]*//g'`
        if echo $nvar $nmax | awk '{exit !( $1 > $2)}'; then max=$var; fi
    done
    echo $max
}



cd $basedir
wget=`which wget`
$wget -N --trust-server-names $DOWNLOAD

extension=".jar"
prefix="craftbukkit"
linkname=$prefix$extension
let counter=1

while [ -f $linkname ]
do
    [ -L $linkname ] && rm $linkname || linkname=$prefix~$counter$extension
    let counter=counter+1
done

allFiles="`ls $prefix*|grep -i $extension`"
list=`removeSymlinks $allFiles`
if [ "$list" == "" ]; then echo "$prefix*$extension not found!"; exit; fi
ln -s $(findMax $list) $linkname