#!/usr/bin/perl -w
@t = qw( aaaa bbbb ccccccc dddddd );
$i = -1;
# the 2nd semicolon is not required, but adds clarity
@n = map {$i+=2; if ($i%5==0){$i+=2}; $i." ".$_} @t;
print map {$_."\n"} @n;