Sorry, i missed the underscore in BEGIN_TAG, and i even thought i remembered going up to look to make sure. That meant that BEGIN_TAG didnt serve as the ending trigger like it should have, instead i was looking for "BEGIN TAG" with a space. So this would fix my example.

open(FILE1, $ARGV[0]) || die "Error: $!\n";
my $save=0; 
my $saveto=''; 
while (my $line=<FILE1>){
  chomp $line; 
  my @parts=split(' ',$line,2); 
  if ( (!$save) && $parts[0] eq 'X1') { $saveto=$parts[1]; $save=1; } 
  elsif ($parts[0] eq 'X2' 
      ||($parts[0] eq 'BEGIN_TAG' ) ){ 
       print $saveto."\n" if ($saveto) ; 
       $saveto=''; 
       $save=0; 
       } 
  elsif ($save) { $saveto.=' '.$line;); } 
  }
print $saveto."\n" if ($saveto) ;
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And you never said you wanted to capture all of them to the end, so after each set was complete (bu hitting X2 or (now fixed to ) BEGIN_TAG i printed it, AND reset $saveto to blank. When you commented out the print, you didnt comment out the reset to blank, so only the last set was saved.