Script that generates a unique local address (ULA) with a /48 prefix using a Pseudo-Random Global ID Algorithm from RFC 4193

generate-rfc4193-address

#!/bin/bash
# The script generates a unique local address (ULA) with a /48 prefix
# using a Pseudo-Random Global ID Algorithm from RFC 4193

PATH=/usr/local/bin:/bin:/usr/bin:/usr/sbin:/sbin
DEBUG=0

log () {
        if [ ! -z "${DEBUG}" ] && [ "${DEBUG}" == "1" ]; then
                echo "$1" >&2
        fi
}

INTERFACE=$1
if [ -z "${INTERFACE}" ]; then
        echo "Usage: ${0} interface"
        exit 1
fi

if [ ! -f "/sys/class/net/${INTERFACE}/address" ]; then
        echo "Interface ${INTERFACE} not found!"
        exit 1
fi

for CMD in date sha1sum sed cut; do
        if hash "${CMD}" 2>/dev/null; then
                eval "${CMD^^}"='$(command -v ${CMD})'
                log "Command ${CMD} found!"
        else
                echo "${CMD} not found!"
                exit 1
        fi
done

#   The algorithm described below is intended to be used for locally
#   assigned Global IDs.  In each case the resulting global ID will be
#   used in the appropriate prefix as defined in RFC 4193 Section 3.2.

#     1) Obtain the current time of day in 64-bit NTP format (RFC 1305).

NTPDATE=$(printf "%08x%08x\n" $(($(${DATE} +%s) + 2208988800)) $(${DATE} +%N | ${SED} "s/0*//"))
log "64-bit NTP format: ${NTPDATE}"

#     2) Obtain an EUI-64 identifier from the system running this
#        algorithm.  If an EUI-64 does not exist, one can be created from
#        a 48-bit MAC address as specified in RFC 3513.  If an EUI-64
#        cannot be obtained or created, a suitably unique identifier,
#        local to the node, should be used (e.g., system serial number).

IFS=':'; set $(</sys/class/net/${INTERFACE}/address); unset IFS
EUI64=$(printf "fe80%x%x%x%x%x" 0x$(( 0x${1} ^ 0x02 )) 0x${2} 0x${3}ff 0xfe${4} 0x${5}${6})
log "EUI-64: ${EUI64}"

#     3) Concatenate the time of day with the system-specific identifier
#        in order to create a key.

CONCAT="${NTPDATE}${EUI64}"
log "Concatenated: ${CONCAT}"

#     4) Compute an SHA-1 digest on the key as specified in RFC 3174;
#        the resulting value is 160 bits.

DIGEST=$(echo ${CONCAT} | ${SHA1SUM} | ${CUT} -c1-40)
log "SHA-1 digest: ${DIGEST}"

#     5) Use the least significant 40 bits as the Global ID.

GLOBALID=$(echo ${DIGEST} | ${CUT} -c31-40)
log "Global ID: ${GLOBALID}"

#     6) Concatenate FC00::/7, the L bit set to 1, and the 40-bit Global
#        ID to create a Local IPv6 address prefix.

IPV6=$(echo fd${GLOBALID} | ${SED} "s|\(....\)\(....\)\(....\)|\1:\2:\3::/48|" | ${SED} "s/:0*/:/g")
log "IPv6: ${IPV6}"

echo ${IPV6}

Line 51 should be:
EUI64=$(printf "fe80%x%x%x%x%x" $(( 0x${1} ^ 0x02 )) 0x${2} 0x${3}ff 0xfe${4} 0x${5}${6})