A bash function wrapper for lsof to find any listening processes.

listening.sh

listening() {
    if [ -z "$1" ]; then

        lines=$(lsof -P -s TCP:LISTEN -i TCP | tail -n +2)
        pairs=$(echo -n "$lines" | awk '{split($9,a,":"); print $2":"a[2]}' | uniq)
        format_string="%5s %5s %s\n"

        if [ -n "$pairs" ]; then
            printf "$format_string" "PORT" "PID" "COMMAND"
            for pair in $pairs; do
                port="${pair/#*:}"
                proc="${pair/%:*}"
                cmnd="$(ps -p "$proc" -o command=)"

                printf "$format_string" "$port" "$proc" "${cmnd:0:$COLUMNS-12}"
            done
        fi

    else

        pid=$(lsof -P -s TCP:LISTEN -i TCP:"$1" -t | uniq)
        if [ -n "$pid" ]; then
            ps -p "$pid" -o pid,command
        fi

    fi
}