Old Perl Version ...

Indeed. The  \K special escape was introduced with 5.10. The following works pre-5.10, but we're back to a look-back. Oh, well... 

>perl -wMstrict -le
"print $];
 my $ma = '525400eb8b36';
 $ma =~ s{ (?<= \G ..) \B }{:}xmsg;
 print qq{'$ma'};
"
5.008009
'52:54:00:eb:8b:36'

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In reply to Re^4: Insert colons into a MAC address by AnomalousMonk
in thread Insert colons into a MAC address by mantager

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