Bash function to canonicalize MAC addresses

posted 2010-08-11 20:36:02, link to this article

I was playing with some network related stuff this evening and needed to rewrite MAC addresses to the canonical form. That is, something like this 00-02-DE-AD-BE-EF.
Why, you ask? Well every piece of software seems to have their own ideas on how to represent these magical 48 bit integers.
For instance, you'll often see something like 01:02:03:C0:FF:EE, which might also be written in shorthand as 1:2:3:c0:ff:ee or as a (pretty Cisco specific) perversion like 0102.03c0:ffee.
Indeed, a lot of variation...which makes parsing, a bit hellish.

Well I had written a pretty elegant parser in Perl before, that thing groks almost anything that you can throw at it.
But today I wanted to implement this in hesschlib, hesschlib is my private library of practical Bash functions. One of the rules of hesschlib is that things should be done in Bash whenever possible.
So I kludged up a small Bash function that does a pretty good job in rewriting most forms of MAC addresses that came to mind to the canonical form. Here it is:

# canonicalize MAC addresses (does grok most forms)
function maccanon {
    canon=''; for octet in ${1//[\.:-]/ }; do 
        [ ${#octet} -eq 4 ] && octet="${octet:0:2} ${octet:2:2}" ; 
        [ ${#octet} -eq 1 ] && octet="0${octet}"; canon=${canon}${canon:+ }${octet}; 
    done; echo ${canon// /-}; 
}

Which is a one-liner in hesschlib, of course, but broken up a bit here to make it more legible.
And finally, here's an example of maccanon in action:

    hessch@turing:~$ for mac in 00:02:DE:AD:BE:EF 1:2:3:c0:ff:ee 0102.03c0:ffee
    > do
    > maccanon ${mac}
    > done

    00-02-DE-AD-BE-EF
    01-02-03-c0-ff-ee
    01-02-03-c0-ff-ee