mjhjmtu

How can I convert a Mac address into an ipv6 Link-Local address?

you have to add fe80:: at the start and insert ff:fe in the middle

furthermore all leading zeros must be stripped

You can use IFS to split the MAC address into 6 colon-separated groups and assemble them. You'll also need to flip the 7th most significant bit (thanks bahamat), i.e. bit 1 of the first byte.

mac_to_ipv6 () 
 IFS=':'; set $1; unset IFS
 ipv6_address="fe80::$(printf %02x $((0x$1 ^ 2)))$2:$3ff:fe$4:$5$6"

You can use the prefix and suffix stripping constructs $VAR#PREFIX and $VAR%SUFFIX to cut the MAC address into pieces.

mac_to_ipv6 () 
 mac=$1
 ipv6_address=fe80::$(printf %02x $((0x$mac%%:* ^ 2)))
 mac=$mac#*:
 ipv6_address=$ipv6_address$mac%:*:*:*ff:fe
 mac=$mac#*:*:
 ipv6_address=$ipv6_address$mac%:*$mac##*:

You can use the substring construct (bash only, not sh).

mac_to_ipv6 () 
 local mac=$1 byte0
 printf %02x -v byte0 $((0x$mac:0:2 ^ 2))
 ipv6_address="fe80::$byte0$mac:3:5ff:fe$mac:9:5$mac:15:2"

Taking Gilles' explanation, but correctly flipping the 7th bit as per IPv6 spec:

#!/bin/bash

IFS=':'; set $1; unset IFS
printf "fe80::%x%x:%x:%x:%xn" 0x$(( 0x$1 ^ 0x02 )) 0x$2 0x$3ff 0xfe$4 0x$5$6

Example of bit-flipping:

$ mac_to_ipv6 00:00:00:00:00:00
fe80::200:00ff:fe00:0000

You can create a function, that uses IFS to split the MAC address into 6 colon-separated groups and assembles them. You'll also need to flip the 7th most significant bit (thanks bahamat), i.e. bit 1 of the first byte:

mac_to_ipv6_ll() 
 IFS=':'; set $1; unset IFS
 echo "fe80::$(printf %02x $((0x$1 ^ 2)))$2:$3ff:fe$4:$5$6"

Usage example:

$ mac_to_ipv6_ll 12:34:56:78:90:12
fe80::1034:56ff:fe78:9012