is_googlebot_ip.sh

# run the 'host' command, but timeout after 30 seconds.
#
# args:
# - parameter to pass to 'host'
# - file to send output of 'host' to
#
# returns:
#  1 => lookup timedout
#  0 => successful run
function timeout_host() {
    local timeout=30
    host $1 > $2 &
    local PID=$!
    while [ $timeout -gt 0 ]; do
        kill -0 $PID > /dev/null 2>&1
        [ $? -eq 1 ] && break
        timeout=$((timeout-1))
        sleep 1
    done
    if [ $timeout -eq 0 ]; then
        kill -9 $PID
        return 1
    else
        return 0
    fi
}

# given an IP address, determine or not whether it is a googlebot host
#
# args:
# - ip address to evaluate
#
# returns:
#  0 => host is a googlebot host
#  1 => host is not a googlebot host
#  2 or 3 => 'host' function timed out
function is_googlebot_ip() {
    local is_googlebot=1
    local temp_filename=`mktemp`
    timeout_host $1 $temp_filename
    [ $? -eq 1 ] && return 2
    cat $temp_filename | grep googlebot > /dev/null
    if [ $? -eq 0 ]; then
        local candidate_hostname=`cat $temp_filename | sed 's/.*pointer[ ]*\(.*\)/\1/'`
        timeout_host $candidate_hostname $temp_filename
        [ $? -eq 1 ] && return 3
        local address=`cat $temp_filename | sed 's/.*address[ ]*\(.*\)/\1/'`
        [ $candidate_address == $address ] && is_googlebot=0
    fi
    rm -f $temp_filename
    return $is_googlebot
}

thanks for the comments, phil! i'll make some modifications.

in reality, the biggest problem is that doing this type of lookup, en masse, is really slow because the 'host' lookup takes way too long. i'll post a new gist of the java version i hacked together, using InetAddress, and running in $n$ threads (where $n$ usually > 100) simultaneously.