Scribbles for my memory

ss -tlnp and lsof -i :PORT tell you the PID and command name, but for Node.js or Python processes, "node" or "python" alone doesn't tell you which project is running. The working directory is what you actually need — and it's sitting right there in /proc/$pid/cwd.

Put this in ~/.bashrc:

whoseport() {
  if [ -z "$1" ]; then
    sudo ss -tlnp | tail -n +2 | while read -r line; do
      port=$(echo "$line" | grep -oP ':\K[0-9]+(?=\s)')
      pid=$(echo "$line" | grep -oP 'pid=\K[0-9]+' | head -1 | tr -dc '0-9')
      [ -n "$pid" ] && echo "PORT: $port | PID: $pid | CMD: $(ps -p $pid -o comm=) | CWD: $(readlink /proc/$pid/cwd)"
    done
  else
    whoseport | grep 'PORT: '$1
  fi
}

Usage:

$ whoseport 6173
PORT: 6173 | PID: 1326886 | CMD: node | CWD: /home/davidw/Projects/ccode_viewer/server

$ whoseport          # list all listening ports
PORT: 61217 | PID: 1356 | CMD: tailscaled | CWD: /
PORT: 22     | PID: 1385  | CMD: sshd      | CWD: /

A few things that went wrong before arriving at this version:

Don't use an alias for this — $1 in a single-quoted alias gets swallowed by inner sh -c calls, and local variables don't survive xargs boundaries. A function avoids both problems. The tr -dc '0-9' on the PID is not cosmetic — ss output can carry trailing whitespace or newlines that break ps -p with a "process ID list syntax error".