#!/usr/bin/perl
use strict;
use warnings;

my $infile ='test.dat';
my $outfile='out.dat';
my $search ='[HKEY_LOCAL_MACHINE\SOFTWARE\OJ\TEST2]';

my $outstr;

{
  open(my $fh, '<', $infile) or die(qq'ERROR open "$infile" ($!)\n');

  # Zeilenende auf "\n\n" setzen
  local $/="\n\n";

  while(my $block=<$fh>)
  {
    if($block=~/\Q$search\E/)
    {
      $outstr=$block;
      last;
    }
  }
  close($fh);
}

die(qq'Key "$search" not found in $infile') unless($outstr);

{
  open(my $fh, '>', $outfile) or die(qq'ERROR open "$outfile" ($!)\n');
  print $fh $outstr;
  close($fh);
}