I have a list of MAC addresses from two sources that I want to unique and sort. I discovered that some of the address do not have zero padding and some do. I ran into a problem trying to use a regex to zero pad a MAC address.

My sample MAC: 
0:13:46:b:4:31    # input
00:13:46:0b:04:31 # expected output

[download]

The regex I tried was: 
$mac =~ s/(^|:)([\da-f])(:|$)/${1}0${2}${3}/g;

[download]

This gave me:
0:13:46:b:4:31    # input
00:13:46:0b:4:31  # produced
00:13:46:0b:04:31 # expected

[download]

My guess is there is an overlap problem because the regex matches and replaces the : charater and so the : is not available to be mactched for the "4" because it was already used by the "b".

I thought about it for a bit and got around the problem without using a regex.

my @parts = split /:/ , $mac;
foreach (@parts) { if (length == 1) { $_ = "0" . $_; } }
$mac = join ":" , @parts;

[download]

Can someone explain why the regex did not work as I expected or how to make it work as desired?

In reply to Regex overlap in MAC address by superfrink

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