MAC Address Generator (Valid unicast locally administered address)

convert-to-valid-local-unicast-mac.sh

# MAC Address Generator
# Generates valid unicast locally administered addresses by
# setting bit 2 of the first byte and clearing bit 1 of the first byte.
# Documentation: http://www.noah.org/wiki/MAC_address
# Script URL: https://gist.github.com/ben-z/3b18d1608868e6abf2212a435a216803

# https://stackoverflow.com/a/3265767/4527337
function prettyprintmac {
  echo $1 | sed -e 's/../&:/g' -e 's/:$//'
}

function cleaninputmac {
  # takes in any 48-bit (6-byte) hex sequence (12 hex characters) below:
  macaddr=$1
  
  # process the mac address
  macaddr=${macaddr//.} # remove .
  macaddr=${macaddr//:} # remove :
  macaddr=${macaddr//-} # remove -
  macaddr=${macaddr#0x} # remove prefix 0x

  echo $macaddr
}

function isvalidmac {
  macaddr=$(cleaninputmac $1)

  # https://stackoverflow.com/a/7662661/4527337
  case $macaddr in
    ( *[!0-9A-Fa-f]* | "" ) return 1 ;;
    ( * )
      case ${#macaddr} in
        # make sure it is 12 characters
        ( 12 ) return 0 ;; 
        ( * )  return 1 ;;
      esac
  esac    
}

function createunicastlocalmac {
  macaddr=0x$macaddr

  # output the mac address
  printf "%x\n" "$(( (macaddr | 0x020000000000) & 0xfeffffffffff ))"
}

# parse input arguments
# https://stackoverflow.com/a/14203146/4527337
for i in "$@"
do
case $i in
    --stdin)
    USE_STDIN=true
    shift # past argument with no value
    ;;
    *)
          # unknown option
    ;;
esac
done

if [ -z "$USE_STDIN" ]; then
  if ! isvalidmac $1; then
    >&2 echo "\"$1\" is not a valid mac address!"
    >&2 echo "Usage: $0 <mac_addr>"
    >&2 echo "Usage2: $0 --stdin"
    exit 1
  fi

  macaddr=$(cleaninputmac $1)
  echo "Input MAC: $(prettyprintmac $macaddr)"

  outputmac=$(createunicastlocalmac $macaddr)
  echo "Output MAC: $(prettyprintmac $outputmac)"
else
  while IFS= read -r line; do
    if ! isvalidmac $line; then
      >&2 echo "\"$line\" is not a valid mac address!"
      exit 1
    fi
    inputmac=$(cleaninputmac "$line")
    outputmac=$(createunicastlocalmac "$inputmac")
    prettyprintmac $outputmac
  done
fi