Check if a Specific Network Port is Already in Use

#!/bin/bash

# Configuration
TARGET_PORT="8080" # The port number to check

# Function to check port availability
check_port() {
    local port=$1
    
    # Check using lsof (preferred as it also shows process ID)
    if command -v lsof &> /dev/null; then
        if lsof -i :"$port" &> /dev/null; then
            echo "Port $port is IN USE by PID $(lsof -t -i :"$port")"
            return 0 # Port is in use
        else
            echo "Port $port is FREE (lsof)."
            return 1 # Port is free
        fi
    # Fallback to netstat if lsof is not available
    elif command -v netstat &> /dev/null; then
        if netstat -tulnp | grep -q ":$port "; then
            echo "Port $port is IN USE (netstat)."
            return 0 # Port is in use
        else
            echo "Port $port is FREE (netstat)."
            return 1 # Port is free
        fi
    else
        echo "Error: Neither 'lsof' nor 'netstat' found. Cannot check port."
        exit 1
    fi
}

# Main execution
if [ -z "$TARGET_PORT" ]; then
    echo "Error: No port specified. Usage: $0 <port_number>"
    exit 1
fi

if check_port "$TARGET_PORT"; then
    echo "Action needed: Port $TARGET_PORT is occupied."
    # You could add logic here, e.g., kill process, suggest different port
else
    echo "Action: Port $TARGET_PORT is available for use."
fi