A function I keep in my .bashrc for quickly determining what processes are listening on what ports, protocols and interfaces - sorted by port number.

listening.sh

function listening {
    if [ "${1}" = "-h" ]; then
        echo "Usage: listening [t|tcp|u|udp] [ps regex]"
        return
    fi
    DISP="both"
    NSOPTS="tu"
    if [ "${1}" = "t" -o "${1}" = "tcp" ]; then
        DISP="tcp"
        NSOPTS="t"
        shift
    elif [ "${1}" = "u" -o "${1}" = "udp" ]; then
        DISP="udp"
        NSOPTS="u"
        shift
    fi
    FILTER="${@}"
    PORTS_PIDS=$(sudo netstat -"${NSOPTS}"lnp | tail -n +3 | tr -s ' ' | sed -n 's/\(tcp\|udp\) [0-9]* [0-9]* \(::\|0\.0\.0\.0\|127\.[0-9]*\.[0-9]*\.[0-9]*\):\([0-9]*\) .* \(-\|\([0-9-]*\)\/.*\)/\3 \1 \5 \2/p' | sed 's/\(::\|0\.0\.0\.0\)/EXTERNAL/' | sed 's/127\.[0-9]*\.[0-9]*\.[0-9]*/LOCALHOST/' | sort -n | tr ' ' ':' | sed 's/::/:-:/' | sed 's/:$//' | uniq)
    PS=$(sudo ps -e --format '%p %a')
    echo -e '   Port - Protocol - Interface - Program\n-----------------------------------------------'
    for PORT_PID in ${PORTS_PIDS}; do
        PORT=$(echo ${PORT_PID} | cut -d':' -f1)
        PROTOCOL=$(echo ${PORT_PID} | cut -d':' -f2)
        PID=$(echo ${PORT_PID} | cut -d':' -f3)
        INTERFACE=$(echo ${PORT_PID} | cut -d':' -f4)
        if [ "${PROTOCOL}" != "${DISP}" -a "${DISP}" != "both" ]; then
            continue
        fi
        if [ "${PID}" = "-" ]; then
            if [ "${FILTER}" != "" ]; then
                continue
            fi
            printf "%7s - %8s - %9s - -\n" "${PORT}" "${PROTOCOL}" "${INTERFACE}"
        else
            PROG=$(echo "${PS}" | grep "^ *${PID}" | grep -o '[0-9] .*' | cut -d' ' -f2-)
            if [ "${FILTER}" != "" ]; then
                echo "${PROG}" | grep -q "${FILTER}"
                if [ $? -ne 0 ]; then
                    continue
                fi
            fi
            printf "%7s - %8s - %9s - %s\n" "${PORT}" "${PROTOCOL}" "${INTERFACE}" "${PROG}"
        fi
    done
}

Examples.md

Examples

$ listening -h
Usage: listening [t|tcp|u|udp] [ps regex]

$ listening statsd
   Port - Protocol - Interface - Program
-----------------------------------------------
   6060 -      tcp -  EXTERNAL - /usr/bin/statsdaemon
   8125 -      udp -  EXTERNAL - /usr/bin/statsdaemon
   8126 -      tcp -  EXTERNAL - /usr/bin/statsdaemon

$ listening tcp statsd
   Port - Protocol - Interface - Program
-----------------------------------------------
   6060 -      tcp -  EXTERNAL - /usr/bin/statsdaemon
   8126 -      tcp -  EXTERNAL - /usr/bin/statsdaemon

$ listening u statsd
   Port - Protocol - Interface - Program
-----------------------------------------------
   8125 -      udp -  EXTERNAL - /usr/bin/statsdaemon

$ listening 
   Port - Protocol - Interface - Program
-----------------------------------------------
    111 -      tcp -  EXTERNAL - rpcbind
    111 -      udp -  EXTERNAL - rpcbind
    668 -      udp -  EXTERNAL - rpcbind
    774 -      udp - LOCALHOST - rpc.statd -L
   6258 -      tcp - LOCALHOST - /usr/bin/wineserver
   6263 -      tcp - LOCALHOST - /usr/bin/wineserver
  27017 -      tcp - LOCALHOST - /usr/bin/mongod --config /etc/mongodb.conf
  34941 -      udp -  EXTERNAL - /usr/sbin/rpc.mountd --manage-gids
  40170 -      tcp -  EXTERNAL - /usr/sbin/rpc.mountd --manage-gids
  41067 -      udp -  EXTERNAL - rpc.statd -L
  47655 -      tcp -  EXTERNAL - rpc.statd -L
  49396 -      udp -  EXTERNAL - /usr/sbin/rpc.mountd --manage-gids
  51021 -      tcp - LOCALHOST - /opt/google/talkplugin/GoogleTalkPlugin
  52336 -      tcp -  EXTERNAL - /usr/sbin/rpc.mountd --manage-gids
  53725 -      tcp - LOCALHOST - /opt/google/talkplugin/GoogleTalkPlugin
  58024 -      udp -  EXTERNAL - /usr/sbin/rpc.mountd --manage-gids
  60589 -      tcp -  EXTERNAL - /usr/sbin/rpc.mountd --manage-gids