run.sh

#!/usr/bin/env bash
set -euo pipefail

# Load defaults (USER_NAME, IMAGE_NAME, CONTAINER_NAME, SSH_PORT, PORT_START).
SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
# shellcheck disable=SC1091
source "${SCRIPT_DIR}/config.env"

PORT_START="${PORT_START:-2223}"

# Return 0 if the given TCP port is LISTENing on the host, else 1.
host_port_in_use() {
  local p="$1"
  ss -ltn | awk '{print $4}' | grep -Eq "(^|:)${p}$"
}

# Find first available port from a given start.
find_free_port_from() {
  local p="$1"
  while host_port_in_use "${p}"; do
    p=$((p + 1))
  done
  echo "${p}"
}

# True if stdin is a TTY (interactive)
is_interactive() {
  [[ -t 0 ]]
}

pick_ssh_port() {
  # Case 1) User did not specify SSH_PORT -> auto-pick from PORT_START
  if [ -z "${SSH_PORT:-}" ]; then
    find_free_port_from "${PORT_START}"
    return 0
  fi

  # Case 2) User specified SSH_PORT -> try it
  local requested="${SSH_PORT}"

  if ! host_port_in_use "${requested}"; then
    echo "${requested}"
    return 0
  fi

  # Case 2.1) Requested port is busy -> ask user whether to auto-increment or exit
  if ! is_interactive; then
    echo "[!] ERROR: requested SSH_PORT=${requested} is already in use, but no TTY to ask." >&2
    echo "    - Option A: clear SSH_PORT in config.env to auto-pick" >&2
    echo "    - Option B: set SSH_PORT to a free port" >&2
    exit 1
  fi

  echo "[!] Port ${requested} is already in use." >&2
  local suggestion
  suggestion="$(find_free_port_from "${requested}")"
  echo "    Next available port from ${requested} is: ${suggestion}" >&2

  while true; do
    read -r -p "Use ${suggestion} instead? [y/N]: " ans
    case "${ans}" in
      [yY]|[yY][eE][sS])
        echo "${suggestion}"
        return 0
        ;;
      ""|[nN]|[nN][oO])
        echo "[*] Aborted by user." >&2
        exit 1
        ;;
      *)
        echo "Please answer y or n." >&2
        ;;
    esac
  done
}

SELECTED_PORT="$(pick_ssh_port)"

if docker inspect "${CONTAINER_NAME}" >/dev/null 2>&1; then
  docker start "${CONTAINER_NAME}" >/dev/null
  echo "[*] run: started existing container=${CONTAINER_NAME} (image=${IMAGE_NAME})"
  echo "[*] run: note: existing container keeps its original port mapping"
else
  docker run -d \
    -p "${SELECTED_PORT}:22" \
    --name "${CONTAINER_NAME}" \
    "${IMAGE_NAME}" >/dev/null
  echo "[*] run: created container=${CONTAINER_NAME} (image=${IMAGE_NAME})"
  echo "[*] run: ssh port=${SELECTED_PORT}"
fi

# EOF