Answer by heemayl for Output only MAC address on Ubuntu

The easiest way would be to use grep with PCRE:

$ ifconfig -a | grep -Po 'HWaddr \K.*$'74:d4:35:84:34:13  

• grep -P will enable us to use perl compatible Regex

• grep -o will only take the matched portion of the line

• We have matched HWaddr before our desired match (MAC addresses) and then discard HWaddr by \K to print only the MAC addresses.

@Helio has mentioned an important point, this is highly dependent on your language i.e. locale settings. To overcome that you can use the C locale (uses ASCII character set) for this command only:

$ LANG=C ifconfig -a | grep -Po 'HWaddr \K.*$'74:d4:35:84:34:13