While writing a web page that allows users to register new hosts for the campus LAN. Among other bits of info that has to be entered is the ethernet address - something which quite a few users try to enter bogus data in, or at least enter it in one of the many different formats used. This bit of code takes in an ethernet address in all of the formats I've come across so far, and returns the "normalized" version (all caps, 2 char octets, colon seperated) or undef if it's not a valid ethernet address. 
sub verify_ether($){
    my $mac = uc(shift);
    $mac =~ s/-/:/g;

    my @octets;

    if($mac =~ /^[0-9A-F]{12}$/){
        $mac = join(':', unpack("A2" x 6, $mac));
    }elsif ($mac =~  /^(([0-9A-F]{1,2}?):){5}([0-9A-F]{1,2})$/ ){
        @octets = split(/:/, $mac);
        map { if (length($_)==1) { $_ = "0" . $_ } } @octets;
        $mac = join(':', @octets);
    }else{
        return undef;
    }
    return $mac;
}

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In reply to Verify string as ethernet address by fs

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