Show Listener Processes with Detailed Arguments

ShowListeners.sh

#!/usr/bin/env bash

# © 2026, Pandu POLUAN
# SPDX-License-Identifier: MPL-2.0

# This Source Code Form is subject to the terms of the Mozilla Public
# License, v. 2.0. If a copy of the MPL was not distributed with this
# file, You can obtain one at https://mozilla.org/MPL/2.0/.

function show_listeners() {
  netstat -tulpnW |
  awk '
    # Print the header. Note the "@@" in front of "CmdLine" is needed!
    BEGIN {print "Proto", "Local", "Pid", "@@CmdLine"}

    # tcp protocol has an additional column that we need to suppress
    $1 ~ /^tcp/ {$6=""; $0=$0}

    # Generate output only for tcp and udp protocols (including their v6 counterparts)
    $1 ~ /^(tc|ud)p/ {
      $2=$3=$5="";
      $0=$0;
      $0=gensub(/( [0-9]+)\/[^/]+$/, "\\1", "g");
      print $0, "@@" $NF
    }' |
  column -t |
  (
    while read ln; do
      pid=${ln##*@@}
      if [[ $pid = CmdLine ]]; then
        cmd=($pid)
      else
        # /proc/PID/cmdline is null-separated
        readarray -d $'\0' cmd < /proc/${pid}/cmdline
      fi
      echo "${ln/@@*/${cmd[*]}}";
    done
  )
}

show_listeners