Or just perhaps:

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

while (<DATA>)
{
    my $three_lines = $_.<DATA>.<DATA>;
    print $three_lines, "\n";
}

=output
asdfasdf asdfasdf asdfasdf
asdfasdfasdf asdfasdf
someting adfasdf

asdfasdfasdfasdfasdf
asdfasdfasdf
asdfasdfasdfasdfasdfasdf

werwerwerwer
ertertert
zsdfasdfasdf

=cut
__DATA__
asdfasdf asdfasdf asdfasdf
asdfasdfasdf asdfasdf
someting adfasdf
asdfasdfasdfasdfasdf
asdfasdfasdf
asdfasdfasdfasdfasdfasdf
werwerwerwer
ertertert
zsdfasdfasdf
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