freeport: Kill Whatever's Holding Your Port

When a dev server won’t start because the port is already in use, you usually have to look up the PID and kill it by hand. This zsh function does that in one command:

freeport() {
  if [[ $# -ne 1 ]]; then
    print -u2 "usage: freeport <port>"
    return 1
  fi

  local -a pids
  pids=("${(@f)$(lsof -ti ":$1")}")
  pids=("${pids[@]:#}")

  if (( ${#pids[@]} == 0 )); then
    print "No process found on port $1"
    return 0
  fi

  kill "${pids[@]}"
}

Usage: freeport 3000.

lsof -ti :3000 finds the PIDs holding the port; the rest just splits the output into an array and kills them. It sends SIGTERM rather than kill -9, so the process gets a chance to shut down cleanly.

It needs lsof, which ships with macOS and most Linux distributions.