✨ feat: Add ARP interface finder script and README (#33)

* ✨ feat: Add ARP interface finder script and README

This commit adds a new script, `run.sh`, that finds all usable network
interfaces for `arp-scan` and exports them to a configuration file. The
script detects interfaces that are "UP" (usable for scanning), skips
virtual container interfaces (veth), and handles special cases like
`eth0@if46` that might be in different network namespaces.

Additionally, a README file is added to provide instructions on how to
run the command.

* ✨ feat(arp-iface-finder): Use bash shebang for portability

Modify the shebang line in the `run.sh` script to use `#!/usr/bin/env bash`
instead of `#!/bin/bash`. This ensures the script will run on systems
where the bash binary is not located at `/bin/bash`, improving
portability.

arp-iface-finder/README.md

@@ -0,0 +1,9 @@
+# Run command
+
+```bash
+bash -c "$(wget -qLO - https://raw.githubusercontent.com/bigbeartechworld/big-bear-scripts/master/arp-iface-finder/run.sh)"
+```
+
+# Description
+
+This script will find all usable network interfaces for arp-scan.

arp-iface-finder/run.sh

@@ -0,0 +1,100 @@
+#!/usr/bin/env bash
+
+# Colors for better output
+RED='\033[0;31m'
+GREEN='\033[0;32m'
+YELLOW='\033[1;33m'
+BLUE='\033[0;34m'
+NC='\033[0m' # No Color
+
+# This script finds active network interfaces for arp-scan and exports them to a config file.
+# It detects interfaces that are "UP" (usable for scanning), skips virtual container interfaces (veth),
+# and handles special cases like eth0@if46 that might be in different network namespaces.
+
+# Function to get and filter usable network interfaces with their states
+get_usable_interfaces() {
+    # Capture the output of 'ip link show' once to list all network interfaces
+    # We use this single call to avoid issues with repeated calls failing for namespaced interfaces
+    ip link show | 
+    # Filter for lines starting with a number (interface entries), exclude loopback (lo)
+    grep -E '^[0-9]+:' | grep -v 'lo:' | 
+    # Process each line of output
+    while read -r line; do
+        # Extract the interface name (e.g., eth0@if46) from the line, removing whitespace
+        iface=$(echo "$line" | awk -F: '{print $2}' | tr -d ' ')
+        
+        # Skip virtual Ethernet (veth) interfaces used by containers, as they’re not useful for general scanning
+        if [[ "$iface" =~ ^veth ]]; then
+            continue
+        fi
+        
+        # Check if the interface has "UP" in its flags, meaning it’s active and usable
+        if echo "$line" | grep -q "<.*,UP"; then
+            # Extract the state (e.g., UP, DOWN) from the line
+            state=$(echo "$line" | grep -o "state [A-Z]*" | awk '{print $2}')
+            # Output the interface name and state, separated by | for later parsing
+            echo "$iface|$state"
+        fi
+    done | 
+    # Remove duplicates and sort the list
+    sort -u
+}
+
+# Display Welcome
+echo -e "${BLUE}========================================${NC}"
+echo -e "${GREEN}BigBear ARP Interface Finder V0.1${NC}"
+echo -e "${BLUE}========================================${NC}"
+echo "Here are some links:"
+echo "https://community.bigbeartechworld.com"
+echo "https://github.com/BigBearTechWorld"
+echo ""
+echo "If you would like to support me, please consider buying me a tea:"
+echo "https://ko-fi.com/bigbeartechworld"
+echo ""
+
+# Get the list of usable interfaces and store it in an array
+# The < <() syntax feeds the function output into mapfile
+mapfile -t interface_lines < <(get_usable_interfaces)
+
+# If no usable interfaces are found, exit with an error
+if [ ${#interface_lines[@]} -eq 0 ]; then
+    echo "No usable interfaces found!"
+    exit 1
+fi
+
+# Initialize an array to store the final list of interface names
+usable_interfaces=()
+
+# Loop through each interface line to extract details and display them
+for line in "${interface_lines[@]}"; do
+    # Split the line into interface name and state using | as the delimiter
+    iface=$(echo "$line" | cut -d'|' -f1)
+    state=$(echo "$line" | cut -d'|' -f2)
+    
+    # Try to get the IP address for the interface; suppress errors if it fails (e.g., namespace issues)
+    ip_addr=$(ip addr show "$iface" 2>/dev/null | grep 'inet ' | awk '{print $2}' | cut -d'/' -f1)
+    # If no IP is found (e.g., due to namespace mismatch), set a default message
+    [ -z "$ip_addr" ] && ip_addr="No IP"
+    
+    # Display the interface details for the user
+    echo "Found usable interface: $iface (IP: $ip_addr, State: $state)"
+    
+    # Add the interface name to the array
+    usable_interfaces+=("$iface")
+done
+
+# Combine all usable interface names into a single space-separated string
+IFACES="${usable_interfaces[*]}"
+echo -e "\nUsable interfaces detected: $IFACES"
+
+# Prepare the export command for the config file
+echo -e "\nGenerated configuration:"
+echo "export IFACES=\"$IFACES\""
+
+# Write the export command to a file that can be sourced later
+# This creates arp_scan_config.sh with the IFACES variable set
+echo "export IFACES=\"$IFACES\"" > arp_scan_config.sh
+
+# Tell the user how to use the generated config file
+echo -e "\nConfiguration saved to arp_scan_config.sh"
+echo "Source the file with: source ./arp_scan_config.sh"