Below is a useful script when you want to see which processes are using a specific port.
#!/bin/bash
# Port Monitor Script for macOS
# Usage: ./port_monitor.sh <port_number>
# Check if port number is provided
if [ $# -eq 0 ]; then
echo "Usage: $0 <port_number>"
echo "Example: $0 8080"
exit 1
fi
PORT=$1
# Validate port number
if ! [[ $PORT =~ ^[0-9]+$ ]] || [ $PORT -lt 1 ] || [ $PORT -gt 65535 ]; then
echo "Error: Please provide a valid port number (1-65535)"
exit 1
fi
# Function to display processes using the port
show_port_usage() {
local timestamp=$(date "+%Y-%m-%d %H:%M:%S")
# Clear screen for better readability
clear
echo "=================================="
echo "Port Monitor - Port $PORT"
echo "Last updated: $timestamp"
echo "Press Ctrl+C to exit"
echo "=================================="
echo
# Check for processes using the port with lsof - both TCP and UDP
if lsof -i :$PORT &>/dev/null || netstat -an | grep -E "[:.]$PORT[[:space:]]" &>/dev/null; then
echo "Processes using port $PORT:"
echo
lsof -i :$PORT -P -n | head -1
echo "--------------------------------------------------------------------------------"
lsof -i :$PORT -P -n | tail -n +2
echo
# Also show netstat information for additional context
echo "Network connections on port $PORT:"
echo
printf "%-6s %-30s %-30s %-12s\n" "PROTO" "LOCAL ADDRESS" "FOREIGN ADDRESS" "STATE"
echo "--------------------------------------------------------------------------------------------"
# Show all connections (LISTEN, ESTABLISHED, etc.)
# Use netstat -n to show numeric addresses
netstat -anp tcp | grep -E "\.$PORT[[:space:]]" | while read line; do
# Extract the relevant fields from netstat output
proto=$(echo "$line" | awk '{print $1}')
local_addr=$(echo "$line" | awk '{print $4}')
foreign_addr=$(echo "$line" | awk '{print $5}')
state=$(echo "$line" | awk '{print $6}')
# Only print if we have valid data
if [ -n "$proto" ] && [ -n "$local_addr" ]; then
printf "%-6s %-30s %-30s %-12s\n" "$proto" "$local_addr" "$foreign_addr" "$state"
fi
done
# Also check UDP connections
netstat -anp udp | grep -E "\.$PORT[[:space:]]" | while read line; do
proto=$(echo "$line" | awk '{print $1}')
local_addr=$(echo "$line" | awk '{print $4}')
foreign_addr=$(echo "$line" | awk '{print $5}')
printf "%-6s %-30s %-30s %-12s\n" "$proto" "$local_addr" "$foreign_addr" "-"
done
# Also check for any established connections using lsof
echo
echo "Active connections with processes:"
echo "--------------------------------------------------------------------------------------------"
lsof -i :$PORT -P -n 2>/dev/null | grep -v LISTEN | tail -n +2 | while read line; do
if [ -n "$line" ]; then
echo "$line"
fi
done
else
echo "No processes found using port $PORT"
echo
# Check if the port might be in use but not showing up in lsof
local netstat_result=$(netstat -anv | grep -E "\.$PORT ")
if [ -n "$netstat_result" ]; then
echo "However, netstat shows activity on port $PORT:"
echo "$netstat_result"
fi
fi
echo
echo "Refreshing in 20 seconds... (Press Ctrl+C to exit)"
}
# Trap Ctrl+C to exit gracefully
trap 'echo -e "\n\nExiting port monitor..."; exit 0' INT
# Main loop - refresh every 20 seconds
while true; do
show_port_usage
sleep 20
done
