Use shell script to check port status on multiple servers

#!/usr/bin/env bash

IP_FILE="${1:-ips.txt}"
PORT=25
CONNECT_TIMEOUT=5

has_cmd() { command -v "$1" >/dev/null 2>&1; }

if [[ ! -f "$IP_FILE" ]]; then
  echo "ERROR: Input file not found: $IP_FILE" >&2
  exit 1
fi

# Prefer nc (more predictable), else use telnet+timeout
TOOL=""
if has_cmd nc; then
  TOOL="nc"
elif has_cmd telnet && has_cmd timeout; then
  TOOL="telnet"
else
  echo "ERROR: Need nc OR telnet+timeout installed." >&2
  exit 1
fi

echo "== SMTP Port 25 Check =="
echo "Hosts file: $IP_FILE | Timeout: ${CONNECT_TIMEOUT}s | Tool: $TOOL"
echo "--------------------------------------------------------"

ok=0; to=0; fail=0; processed=0

while IFS= read -r host; do
  host="${host//$'\r'/}"     # remove CR (Windows CRLF)
  host="$(echo "$host" | xargs)"  # trim whitespace

  [[ -z "$host" ]] && continue
  [[ "$host" =~ ^# ]] && continue

  processed=$((processed + 1))
  echo "[$processed] Checking $host:$PORT ..."

  if [[ "$TOOL" == "nc" ]]; then
    out="$(nc -vz -w "$CONNECT_TIMEOUT" "$host" "$PORT" 2>&1)"
    rc=$?
    if [[ $rc -eq 0 ]]; then
      echo "  -> CONNECTED"
      ok=$((ok+1))
    else
      if echo "$out" | grep -Eqi "(timed out|timeout)"; then
        echo "  -> TIMEOUT"
        to=$((to+1))
      else
        echo "  -> FAILED"
        fail=$((fail+1))
      fi
    fi
  else
    out="$(timeout "$CONNECT_TIMEOUT" bash -c "echo QUIT | telnet $host $PORT" 2>&1)"
    rc=$?
    if [[ $rc -eq 124 ]]; then
      echo "  -> TIMEOUT"
      to=$((to+1))
    elif echo "$out" | grep -Eqi "(Connected to|220[ -])"; then
      echo "  -> CONNECTED"
      ok=$((ok+1))
    else
      echo "  -> FAILED"
      fail=$((fail+1))
    fi
  fi

done < "$IP_FILE"

echo "--------------------------------------------------------"
echo "Summary:"
echo "  CONNECTED: $ok"
echo "  TIMEOUT:   $to"
echo "  FAILED:    $fail"
echo "  TOTAL:     $processed"