MacOs: How to see which processes are using a specific port (eg 443)

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