So part of what I am doing at my current job is helping one of the Unix admins with DNS and DHCP. For the DHCP portion to setup the reservations we need the MAC addy in a certain format, of which the people requesting never seem to get consistently right, so I wrote a small shell script (it’s still rough) that will normalize the MAC address for what we need (colon separated, alpha characters lower case).

[Edit: the below only works on FreeBSD and Linux, for Solaris swap the awk '{print tolower($0)}' with tr '[:upper:]‘ ‘[:lower:]‘ <- or you could just do that for all of them as well).

#!/usr/bin/env sh
 
mac="$1"
 
#check to see if input is empty
if [ ! -n "$mac" ]
    then
        echo "Please enter a MAC address."
        exit
else 
    # echo the input, strip out dot(.), strip out colon(:), strip out dash(-)
    # add colon(:) every two chars, remove last colon(:)
    # awk to lowercase characters [EDIT: updated the sed for . seps and escape]
    echo $mac | sed -e 's/\.//g' -e 's/\://g' -e 's/\-//g' -e 's/../&:/g' -e 's/:$//g' \
| awk '{print tolower($0)}'
fi

Some of the standard formats we see are:
1A:BC:35:57:33:08
1A-BC-35-57:33:08
1ABC35573308
1abc35573308
1a.bc.35.57.33.08
1A.BC.35.57.33.08

The script will take all of these and make them look like: 1a:bc:35:57:33:08.

Here is the breakdown for those that are curious:
1. if [ ! -n "$mac" ] checks to make sure first input variable is not empty.
2. echo $mac outputs the first argument (does not do any input validation)
3. The sed is in five parts:

[Edited to escape the sequences, just in case they should have special meaning]
    a. 's/\.//g' strips out the period should it be in that format
    b. 's/\://g' strips out the colons should they be there (to avoid extra colons)
    c. 's/\-//g' strips out the dashes should they be in that format
    d. 's/../&:/g' every two characters append a colon
    e. 's/:$//g' remove the last trailing colon

4. awk ‘{print tolower($0)}’ make all of the upper case alpha chars lower case to match our format needs.
4a. tr ‘[:upper:]‘ ‘[:lower:]‘ for Solaris (yes I know tr ‘[A-Z]‘ ‘[a-z]‘ will work as well, but this is easier to read IMHO)

This will work on a file full of MAC addresses, just throw it in a for loop (this is if you name the file macnorm.sh):

for i in `cat filename`; do ./macnorm.sh $i; done

Again it is important to realize that there is no checking of the input, so if you did it over /etc/passwd it would add a colon (:) every two characters. Hope this helps.

-Scott.

Tags: awk, DHCP, sed, shell

This entry was posted on Sunday, August 7th, 2011 at 14:19:23 and is filed under System Administration. You can follow any responses to this entry through the RSS 2.0 feed. Responses are currently closed, but you can trackback from your own site.