1. Use a flag. 2. If you read a file as you mentioned, do not use arrays at all:

open my $fh,'<', $filename or die $!;

my $flag;
while( <$fh> ){

   unless( $flag ){
      next unless /^start_mark/;
      $flag = 1;
   }
   elsif( /^end_mark/ ){
      
      $flag = 0;
   }
}
continue {
   print if $flag
}

close $fh;
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