CODEWITHSUNDEEP
bashmacoshexdecimal
Tom
Tom

Reputation: 1618

BASH Increment MAC Address

I've got a valid mac address in a var called oldMAC I need to increment this and then return a new valid MAC Address.

In this example I'm incrementing by 1, but it could be by any value.

So far I've got the following:

echo $oldMAC
mac=$(echo $oldMAC |  tr '[:lower:]' '[:upper:]' | tr -d ':') # upper case and remove :
echo $mac

macdec=$( printf '%d\n' 0x$mac ) # convert to decimal
echo $macdec

macadd=$( expr $macdec + 1 ) # add 1
echo $macadd

machex=$( printf '%X\n' $macadd ) # convert to hex
echo $machex

This outputs:

00:12:34:ae:BC:EF (oldMAC)
001234AEBCEF (mac)
78193278191 (macdec)
78193278192 (madadd)
1234AEBCF0 (machex)

The issue I have is working out how to convert 1234AEBCF0 so it returns as 00:12:34:AE:BC:F0

Can anyone advise how to do this... or is there a better way ?

Thanks

Upvotes: 2

Views: 2779

Answers (2)

Seandex
Seandex

Reputation: 129

Just need to change 2 lines.

mac=$(echo $oldMAC | tr '[:lower:]' '[:upper:]' | tr -d ':')

to

 mac=$(echo $oldMAC | sed s/":"//g)

and then

machex=$( printf '%X\n' $macadd )

to

machex=$( printf '%X\n' $macadd |tee|tr A-Z a-z)

overall

mac=$(echo $oldMAC|sed s/":"//g)
macdec=$(printf '%d\n' 0x$oldmac)
macadd=$(expr $macdec + 1)
machex=$( printf '%X\n' $macadd |tee|tr A-Z a-z)

Upvotes: 1

Jan Hudec
Jan Hudec

Reputation: 76306

sed to rescue:

macnew=$(echo $machex | sed 's/../&:/g;s/:$//')

The pattern is

+------------ substitute
|  +--------- any two characters
|  | +------- with the whole match
|  | |+------ and :
|  | || +---- all occurrences, utilizing the fact it means non-overlapping
|  | || |+------- another command
|  | || ||+------ substitute
|  | || ||  +---- :
|  | || ||  |+--- at the end of line
|  | || ||  || +- with nothing to get rid of the trailing :
V  V VV VV  VV V
s/../&:/g;s/:$//

You also need to make sure 12 digits are actually printed. The printf command can do that, just make the pattern "%012x"—0 means pad with 0s (instead of spaces) and 12 is the minimum width. Use uppercase X for uppercase hex digits and lowercase x for lowercase hex digits.

You can simplify the addition a bit by using the bash's built-in arithmetic expansion, which understand hexadecimal output directly, and understands both upper and lowercase, so you only need to drop the :s:

mac=$(echo $oldMAC | tr -d ':')
macadd=$(( 0x$mac + 1 ))

It still comes back as decimal, so you still need the printf "%012x" to convert it. You can pipe it directly to the sed to keep it short.

macnew=$(printf "%012x" $macadd | sed 's/../&:/g;s/:$//')

Upvotes: 2

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