This one does not suck the whole file into memory, so can handle large amounts of data:

use strict;
use warnings;

local $/="|"; # Record Separator
my @buf;
while (<DATA>){
  #next unless $_=~/\w/; # Ignore Blank ("\n" lines
  s/\n//; # Zap newlines 
  push @buf,$_;
  Print_It() if (3==@buf);
}
Print_It();
#---------------------
sub Print_It{
      print join("",@buf),"\n";
      @buf=();
}
__DATA__
a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|
s|t|u|v|w|x|y|z|A|B|C|D|E|F|G|H|I|J|
K|L|M|N|O|P|Q|R|S|T|U|V|W|X|Y|Z|1|2|
3|4|5|6|7|8|9|10|11|12|13|14|15|16|17|
18|19|20
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