Retrieve the MAC address of a network interface on a local or remote host (macOS or Linux)

getmacaddress.sh

#!/usr/bin/env bash
# -----------------------------------------------------------------------------
# getmacaddress.sh
#
# Retrieve the MAC address of a network interface on a local or remote host.
#
# The script connects to the specified host (via SSH if the host is not the
# local machine) and attempts to retrieve the MAC address of the specified
# network interface.
#
# Behaviour:
#   - If no interface is specified, the script defaults to "en0".
#   - If the interface exists, the MAC address is printed to stdout.
#   - If the interface does not exist, the script lists available interfaces
#     and prompts the user to select one interactively.
#
# The script supports both macOS and Linux systems:
#   - macOS: uses `ifconfig` to obtain the MAC address
#   - Linux: reads `/sys/class/net/<interface>/address`
#
# Rationale:
#   Many modern Linux distributions no longer install the legacy
#   `net-tools` package by default (which provides `ifconfig`). Rather
#   than assuming its presence, the script reads the MAC address
#   directly from `/sys/class/net`, which is part of the standard
#   Linux kernel sysfs interface and is available on virtually all
#   Linux systems.
#
# SSH is only used when the requested host differs from the local hostname
# (case-insensitive comparison).
#
# Usage:
#   getmacaddress.sh <host> [interface]
#
# Examples:
#   getmacaddress.sh computername1.local
#   getmacaddress.sh computername2.local enp1s0
#   getmacaddress.sh computername3.local en1
#
# Arguments:
#   host        Target hostname or SSH host alias
#   interface   Optional network interface (default: en0)
#
# Exit codes:
#   0  Success (MAC address printed)
#   1  Invalid input
#   2  Interface not found or MAC address could not be determined
#
# Requirements:
#   - bash (compatible with macOS bash 3.2+)
#   - ssh (for remote hosts)
#   - ifconfig (macOS) or /sys/class/net (Linux)
#
# Installation (optional):
#   To make the script available system-wide, copy it to a directory
#   on your PATH, for example:
#
#       cp getmacaddress.sh /usr/local/bin/getmacaddress
#       chmod +x /usr/local/bin/getmacaddress
#
#   You can then run it from anywhere, e.g.:
#
#       getmacaddress computername.local
#
#   (On macOS and many Linux systems, /usr/local/bin is already included
#   in the default PATH.)
#
# Author: Jeremy Varnham https://github.com/jvarn
# License: MIT
# -----------------------------------------------------------------------------

usage() {
  echo "Usage: $(basename "$0") <host> [interface]"
  echo "Example: $(basename "$0") quark en1"
  echo "If interface is omitted, en0 is used."
}

if [[ -z "$1" ]]; then
  usage
  exit 1
fi

HOST="$1"
INTERFACE="${2:-en0}"

LOCAL_HOST=$(hostname | tr '[:upper:]' '[:lower:]')
TARGET_HOST=$(echo "$HOST" | tr '[:upper:]' '[:lower:]')

# POSIX-sh compatible remote/local commands (NO [[ ... ]])
GET_MAC_CMD='
case "$OSTYPE" in
  darwin*)
    ifconfig '"$INTERFACE"' 2>/dev/null | awk "/ether/{print \$2; exit}"
    ;;
  *)
    cat /sys/class/net/'"$INTERFACE"'/address 2>/dev/null | head -n 1
    ;;
esac
'

LIST_IFACES_CMD='
case "$OSTYPE" in
  darwin*)
    ifconfig 2>/dev/null | awk "
      /^[A-Za-z0-9._-]+:/{iface=\$1; sub(/:$/, \"\", iface)}
      /ether[[:space:]]/{print iface}
    " | sort -u
    ;;
  *)
    for p in /sys/class/net/*/address; do
      iface=${p%/address}; iface=${iface##*/}
      [ "$iface" = "lo" ] && continue
      echo "$iface"
    done | sort -u
    ;;
esac
'

run_cmd() {
  # $1 = command string
  if [[ "$TARGET_HOST" == "$LOCAL_HOST" ]]; then
    sh -c "$1"
  else
    # run using /bin/sh on the remote, but keep the script POSIX-compatible
    ssh "$HOST" "sh -c $(printf '%q' "$1")"
  fi
}

MAC="$(run_cmd "$GET_MAC_CMD" | tr -d '\r' | head -n 1)"

if [[ -n "$MAC" ]]; then
  echo "$MAC"
  exit 0
fi

echo "Interface \"$INTERFACE\" does not exist on $HOST."

#mapfile -t IFACE_ARRAY < <(run_cmd "$LIST_IFACES_CMD" | tr -d '\r')

# Build IFACE_ARRAY (bash 3.2 compatible: no mapfile)
IFACE_ARRAY=()
while IFS= read -r line; do
  [[ -n "$line" ]] && IFACE_ARRAY+=("$line")
done < <(run_cmd "$LIST_IFACES_CMD" | tr -d '\r')

if [[ ${#IFACE_ARRAY[@]} -eq 0 ]]; then
  echo "(No interfaces with a MAC address were detected.)"
  exit 2
fi

echo "Please choose one of the following interfaces:"

for i in "${!IFACE_ARRAY[@]}"; do
  printf "%2d) %s\n" $((i+1)) "${IFACE_ARRAY[$i]}"
done

echo
read -p "Enter number: " CHOICE

if ! [[ "$CHOICE" =~ ^[0-9]+$ ]] || (( CHOICE < 1 || CHOICE > ${#IFACE_ARRAY[@]} )); then
  echo "Invalid selection."
  exit 1
fi

INTERFACE="${IFACE_ARRAY[$((CHOICE-1))]}"

MAC="$(run_cmd "
case \"\$OSTYPE\" in
  darwin*)
    ifconfig $INTERFACE 2>/dev/null | awk '/ether/{print \$2; exit}'
    ;;
  *)
    cat /sys/class/net/$INTERFACE/address 2>/dev/null | head -n 1
    ;;
esac
" | tr -d '\r')"

if [[ -n "$MAC" ]]; then
  echo
  echo "$MAC"
  exit 0
fi

echo "Unable to determine MAC address."
exit 2