You could probably do something like: 
if $str =~ m!\.!
    {$str =~ s/(\.?[0-9a-eA-E]*)/(substr("0$1", -2))/ge;}
else
    {$str =~ s/(:?[0-9a-eA-E]*)/(substr("0$1", -4))/ge;}

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Nuance

In reply to RE: RE: (2) One for the regexp fans (nnnn:nnnn:nnnn) by nuance
in thread One for the regexp fans by Odud

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