try 
#!/usr/local/bin/perl -w
use strict;

$_ = '00a0c801adc6';

s/([\w]{2})(?!$)/$1:/gio, "\n<BR>";

print "$_\n<BR>";

[download]

to explain the regex, 

s/
    ([\w]{2})      # matches a pair of letters/numbers
    (?!$)          # matches NOT end of string (zero-width negative lo
+okahead assertion)
/$1:/giox;         # replace pair with trailing colon

[download]
all this assumes you don't have to untaint the mac address. otherwise, you'll want to do that before the s///.

~Particle

In reply to Re: More Help with Regex by particle
in thread More Help with Regex by lucky1

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